Chapter one - Fire in geologic history
In order to gain perspective on fire’s role in nature throughout geologic history we need to be able to understand geologic history from the formation of the earth billions of years ago to the present. Scientists believe that earth formed about 4.5 billion years ago and life appeared on its surface within one billion years. The similarities between today’s organisms indicate a single common ancestor from which all species diverged.
Fires began in what is known as the Paleozoic Era spanning roughly from 541 to 252.2 million years and is subdivided into six geologic periods, the Cambrian (541.0 – 489.5 million years), Ordovician (489.5 –
445.2 million years), Silurian (445.2 – 423.0 million years), Devonian (445.2 – 372.2 million years), Carboniferous ( 372.2 – 303.7 million years), and the Permian (303.7 – 254.2 million years).
After the Paleozoic, is the Mesozoic era (252.2 – 66.0 million years), which is subdivided into the Triassic (252 – 208.5 million years), the Jurassic (208.5 – 152.1 million years), and the Cretaceous (152.1 - 72.1 million years). Finally we have the Cenozoic era (72.1 million – 11.700 thousand years) and this era is further subdivided into the Paleogene (72.1 – 28.1 million years), Neogene (28.1 – 3.60 million years), and the Quaternary (3.60 million years to 11.700 thousand years). All this is further subdivided, but this should be sufficient to describe fire’s major role in geologic history. Keep in mind that these dates vary by up to a few million years depending how different researchers calculate the dates. [9]
Around 1.2 billion years ago alga scum began to colonize the land and by 450 million years the first land plants emerged and became well established. Land plants were so successful that it is believed they contributed to the late Devonian extinction event. Vegetative fires began with the establishment of land based flora in the Middle Ordovician period 470 million years ago that caused oxygen levels to rise to 13% permitting the possibility of wildfire. Wildfire is first recorded in the fossil record in the Late Silurian, 420 million years ago, as charcoalified plants and wildfire ash in the geologic strata.
Except for a controversial gap in the Late Devonian, charcoal has been present in the fossil record ever since. More detailed information on fire in the Paleozoic along with oxygen levels and fossil charcoal can be found in the scientific paper called The diversification of Paleozoic fire systems and fluctuations in atmospheric oxygen concentration. [10]
Some scientists speculate that wildfire created a positive feedback loop contributing to warmer dryer climates more conducive to fire. Fossilized charcoal is found in chunks where plants are preserved in
great detail or preserved in soot deposits in lakebeds and river deltas. It is believed that fires in low,
scrubby wetlands of the Silurian must have been limited in scope. It was in the Middle Devonian that fire really became widespread according to the fossil record. The Devonian period begins at the end of the Silurian 419.2 million years to the beginning of the Carboniferous period about 358.9 million years ago.
Fires began in what is known as the Paleozoic Era spanning roughly from 541 to 252.2 million years and is subdivided into six geologic periods, the Cambrian (541.0 – 489.5 million years), Ordovician (489.5 –
445.2 million years), Silurian (445.2 – 423.0 million years), Devonian (445.2 – 372.2 million years), Carboniferous ( 372.2 – 303.7 million years), and the Permian (303.7 – 254.2 million years).
After the Paleozoic, is the Mesozoic era (252.2 – 66.0 million years), which is subdivided into the Triassic (252 – 208.5 million years), the Jurassic (208.5 – 152.1 million years), and the Cretaceous (152.1 - 72.1 million years). Finally we have the Cenozoic era (72.1 million – 11.700 thousand years) and this era is further subdivided into the Paleogene (72.1 – 28.1 million years), Neogene (28.1 – 3.60 million years), and the Quaternary (3.60 million years to 11.700 thousand years). All this is further subdivided, but this should be sufficient to describe fire’s major role in geologic history. Keep in mind that these dates vary by up to a few million years depending how different researchers calculate the dates. [9]
Around 1.2 billion years ago alga scum began to colonize the land and by 450 million years the first land plants emerged and became well established. Land plants were so successful that it is believed they contributed to the late Devonian extinction event. Vegetative fires began with the establishment of land based flora in the Middle Ordovician period 470 million years ago that caused oxygen levels to rise to 13% permitting the possibility of wildfire. Wildfire is first recorded in the fossil record in the Late Silurian, 420 million years ago, as charcoalified plants and wildfire ash in the geologic strata.
Except for a controversial gap in the Late Devonian, charcoal has been present in the fossil record ever since. More detailed information on fire in the Paleozoic along with oxygen levels and fossil charcoal can be found in the scientific paper called The diversification of Paleozoic fire systems and fluctuations in atmospheric oxygen concentration. [10]
Some scientists speculate that wildfire created a positive feedback loop contributing to warmer dryer climates more conducive to fire. Fossilized charcoal is found in chunks where plants are preserved in
great detail or preserved in soot deposits in lakebeds and river deltas. It is believed that fires in low,
scrubby wetlands of the Silurian must have been limited in scope. It was in the Middle Devonian that fire really became widespread according to the fossil record. The Devonian period begins at the end of the Silurian 419.2 million years to the beginning of the Carboniferous period about 358.9 million years ago.
The Carboniferous Period extends from 359.2 million years to the beginning of the Permian Period about 299 million years. It seemed that in the Carboniferous fire became very pronounced because
of the high-oxygen, high-biomass of the period. It was at this time that both plants and animals became very adapted to a high fire environment that has continued through the Permian and to this day.
Oxygen levels have been slowly declining since the Carboniferous, but fire has continued to be frequent and widespread all over the world. In some areas native peoples living on the land have increased the frequency of fire for hundreds of thousands of years to improve their livelihood, perhaps countering effects of declining oxygen levels. In Africa and Europe man’s influence goes back hundreds of thousands of years. In Australia man’s
influence seems to have been about 60 thousand years ago, and in the United States plants and animals have adapted to more frequent man caused fire, for tens of thousands of years.
of the high-oxygen, high-biomass of the period. It was at this time that both plants and animals became very adapted to a high fire environment that has continued through the Permian and to this day.
Oxygen levels have been slowly declining since the Carboniferous, but fire has continued to be frequent and widespread all over the world. In some areas native peoples living on the land have increased the frequency of fire for hundreds of thousands of years to improve their livelihood, perhaps countering effects of declining oxygen levels. In Africa and Europe man’s influence goes back hundreds of thousands of years. In Australia man’s
influence seems to have been about 60 thousand years ago, and in the United States plants and animals have adapted to more frequent man caused fire, for tens of thousands of years.
It has not been until modern man, that man’s
activities began to suppress fire. Any misguided attempt to take man out of the fire equation now and revert to less frequent fire before man would completely devastate much of these man enhanced frequent fire ecosystems, perhaps as much or more than fire suppression has already.
Let us begin our study of fire in geologic history with the Paleozoic era. I am going to skip the Cambrian period, the earliest period of the Paleozoic, because if there was any fire at all on land, it did not amount to much. I supposed volcanic fire or lava could have been affecting the
microbial mats growing around shorelines in wetlands and uplands causing adaptive changes. If lightning ignited anything, it must not have traveled very far burning as a low oxygen smoldering fire in a dried out microbial mat.
Fire in the Ordovician
(488.3 – 443.7 million years)
The Ordovician Period lasted 45 million years. The area north of the tropics was mostly ocean with most of the earth’s land mass collected in the supercontinent Gondwana below the tropics. In the Ordovician most of the world’s land mass – Southern Europe, Africa, South America, Antarctica and Australia formed the supercontinent Gondwana. During the early Ordovician, North America straddled the equator and almost the entire continent was underwater.
In the Middle Ordovician, North America rose above water and a tectonic highland corresponding to the later Appalachian Mountains formed on the eastern seaboard. Western and Central Europe were separated, but were moving north to what is today North America. During the Ordovician, Gondwana shifted toward the South Pole with much of it being submerged underwater. Tetrahedral spores similar to primitive land plants of today have been found from the Ordovician showing that plants had colonized the land at this time. Ordovician image [11] Landmass image [11]
As far as I know there is no fossil record of fire in the Ordovician. We can still speculate on the frequency and intensity of fire during this period based upon observing these same vegetative types of plants and their relationship with fire today. It is believed that plants evolved from green algae into primitive liverworts and mosses similar to those today during the Ordovician. During the Ordovician, the microbial mats, fungus and lichens are being supplemented by early mosses and liverworts which we know today build up dead organic material in wet areas. [12]
During times of drought, these peat bogs dry out as in today’s swamps periodically and are set on fire by lightning. The burning out of peat bogs in the Okefenokee Swamp and Everglades, for instance, create open water habitats for plants and animals. This provides a sequence of succession stages as the wetlands once again fill up with dead debris that sinks to the bottom. In this manner nature has used fire to create great diversity of both plant and animal species that occupy these succession stages.
Fire in the Silurian
(443.7 – 416.0 million years)
The Silurian was a time of the melting of large glacial formations. This contributed to a substantial rise in ocean levels and a general stabilization of earth’s climate that had previously been subjected to erratic fluctuations. Coral reefs made their appearance in the shallow seas created by the flooding of large parts of the continents creating limestone rock over time. The fossil record shows that vascular plants made their appearance along with the ancestors of spiders and centipedes of today. Silurian image [13] Landmass image [14]
It would appear that bog fires expanded out of the swamps and onto dry land as vascular plants began to build up accumulations of debris on high ground. Also during the Silurian oxygen levels continued to rise to levels above of what we have today so we know conditions were now ripe for more frequent fire. [15] Plants played a significant role in creating these higher oxygen levels that helped insects and other animals as well as provide needed habitat. It also allowed oxygen levels to get high enough to support fire and flames beyond the smoldering peat fires suppressed by lower oxygen levels.
Wildfire is first recorded in the late Silurian in the fossil record 420 million years ago according to Wikipedia. [16] Fire began to be a natural force to be reckoned with, causing regular vegetative fires in the Silurian. So what were these fires like? It does not look like these fires amounted to much, simply burning out bogs during dry periods, and then extending to higher ground where dead vegetation had built up around the newly evolving land plants.
The ancestors of ferns and horsetails evolved in the Silurian and I have noticed that when the leaves of modern ferns die above ground in wetlands and uplands they burn well. In the spring in the Southeastern United States after a winter fire, the ferns quickly sprout back from beneath the ground with fresh new fronds. Not only does the fire remove the mulching caused by the old dead fronds, it provides new useable nutrients to the sprouting plant helping the plant grow stronger and better.
Fire in the Devonian
(419.2 – 358.9 million years)
The Devonian sees fire and fire adapted plants becoming widespread around the globe. At that time, there was the supercontinent of Gondwana in the south and the continent of Siberia in the north along with the small continent of Euramerica. [17] Wikipedia states:
“The Devonian period experienced the first significant adaptive radiation of terrestrial life. Since large vertebrate terrestrial herbivores had not yet appeared, free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents.” Devonian image [18] Landmass image [19]
“By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods also became well-established. Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the “Age of Fish".”
During the Middle Devonian, plants began to grow taller and larger. It was during this period that the
first trees evolved. [20] It was also at this time that small trees arose growing to about 6 feet high. A tree trunk with an attached crown was discovered in the state of New York (called Eospermatopteris) and was sized up to 8 meters. In the Late Devonian archaeopteris is the best well known tree and is possibly an ancestor of the conifers. This tree reached a height of 18 meters. By the end of the Devonian, the first seed plants had emerged.
In this article titled Newfound Fossils Reveal Secrets of World’s Oldest Forest [21] suggests that trees were already dropping their limbs to the ground providing habitat for animals. The Gilboa Forest dates to 385 million years and these forests were widespread around the world at this time. The article states, “And the trees, like modern palms, likely dropped their branches on a yearly or seasonal cycle, filling the forest floor with woody litter suitable for arthropods such as spiders and insects.”
The Cabbage Palm in the southeastern United States, like many other palms around the world having evolved from these early forests, are a very fire adapted species. The trunks are so fire tolerant that they can be almost burnt down by hot periodic fires and still survive. These palms have very flammable fronds that burn very hot, adapted to most likely burn out the competition from other evolving tree species. I suggest the reason these forests were so widespread is because of this very successful adaptive fire trait.
The above article also states, “Stein noted that these early trees played a major role in establishing Earth's first terrestrial ecosystems. “"Trees really dominate those kinds of environments they're found in. They really are the entire fabric in which an entire ecology fits in a terrestrial realm,"” he said.
Fire in the Carboniferous
(359.2 – 299.0 million years)
The Carboniferous began with vast forests already covering the continents and oxygen levels rose above levels not seen before or since. During the first part of the Carboniferous the coal beds were laid down in warm tropical and subtropical forests that provide much of our energy we use today. Arthropods (modern insects) became very prominent and grew to great size because the higher oxygen
levels. This was a time that the amphibians flourished feeding on insects, and sometimes the Carboniferous is called the age of amphibians and early reptiles. [22]
A minor extinction event occurred in the middle of the Carboniferous caused by a change in climate as continents collided becoming the supercontinent Pangaea. This caused cooling glaciation, and low sea level. I suspect this coming together of the continents also put species of plants and animals isolated on different continents into conflict with each other causing extinctions of less adaptable species.
This cooling and drying of the planet caused the tropical rainforest to collapse into fragments and the more arid lands saw frequent wildfires both of high intensity and low intensity partly created by high oxygen levels. Some scientists speculate that wildfires were of very high intensity because of the high oxygen levels. I and others suspect that the higher oxygen levels just led to more frequent less intense fires, as leaf litter caught fire quicker than it normally would. This was a time of great adaptation to fire by most species of plants and animals because fire was so frequent and intense, perhaps even more than anytime in earth’s history. Carboniferous fire image [23] Landmass image [24]
activities began to suppress fire. Any misguided attempt to take man out of the fire equation now and revert to less frequent fire before man would completely devastate much of these man enhanced frequent fire ecosystems, perhaps as much or more than fire suppression has already.
Let us begin our study of fire in geologic history with the Paleozoic era. I am going to skip the Cambrian period, the earliest period of the Paleozoic, because if there was any fire at all on land, it did not amount to much. I supposed volcanic fire or lava could have been affecting the
microbial mats growing around shorelines in wetlands and uplands causing adaptive changes. If lightning ignited anything, it must not have traveled very far burning as a low oxygen smoldering fire in a dried out microbial mat.
Fire in the Ordovician
(488.3 – 443.7 million years)
The Ordovician Period lasted 45 million years. The area north of the tropics was mostly ocean with most of the earth’s land mass collected in the supercontinent Gondwana below the tropics. In the Ordovician most of the world’s land mass – Southern Europe, Africa, South America, Antarctica and Australia formed the supercontinent Gondwana. During the early Ordovician, North America straddled the equator and almost the entire continent was underwater.
In the Middle Ordovician, North America rose above water and a tectonic highland corresponding to the later Appalachian Mountains formed on the eastern seaboard. Western and Central Europe were separated, but were moving north to what is today North America. During the Ordovician, Gondwana shifted toward the South Pole with much of it being submerged underwater. Tetrahedral spores similar to primitive land plants of today have been found from the Ordovician showing that plants had colonized the land at this time. Ordovician image [11] Landmass image [11]
As far as I know there is no fossil record of fire in the Ordovician. We can still speculate on the frequency and intensity of fire during this period based upon observing these same vegetative types of plants and their relationship with fire today. It is believed that plants evolved from green algae into primitive liverworts and mosses similar to those today during the Ordovician. During the Ordovician, the microbial mats, fungus and lichens are being supplemented by early mosses and liverworts which we know today build up dead organic material in wet areas. [12]
During times of drought, these peat bogs dry out as in today’s swamps periodically and are set on fire by lightning. The burning out of peat bogs in the Okefenokee Swamp and Everglades, for instance, create open water habitats for plants and animals. This provides a sequence of succession stages as the wetlands once again fill up with dead debris that sinks to the bottom. In this manner nature has used fire to create great diversity of both plant and animal species that occupy these succession stages.
Fire in the Silurian
(443.7 – 416.0 million years)
The Silurian was a time of the melting of large glacial formations. This contributed to a substantial rise in ocean levels and a general stabilization of earth’s climate that had previously been subjected to erratic fluctuations. Coral reefs made their appearance in the shallow seas created by the flooding of large parts of the continents creating limestone rock over time. The fossil record shows that vascular plants made their appearance along with the ancestors of spiders and centipedes of today. Silurian image [13] Landmass image [14]
It would appear that bog fires expanded out of the swamps and onto dry land as vascular plants began to build up accumulations of debris on high ground. Also during the Silurian oxygen levels continued to rise to levels above of what we have today so we know conditions were now ripe for more frequent fire. [15] Plants played a significant role in creating these higher oxygen levels that helped insects and other animals as well as provide needed habitat. It also allowed oxygen levels to get high enough to support fire and flames beyond the smoldering peat fires suppressed by lower oxygen levels.
Wildfire is first recorded in the late Silurian in the fossil record 420 million years ago according to Wikipedia. [16] Fire began to be a natural force to be reckoned with, causing regular vegetative fires in the Silurian. So what were these fires like? It does not look like these fires amounted to much, simply burning out bogs during dry periods, and then extending to higher ground where dead vegetation had built up around the newly evolving land plants.
The ancestors of ferns and horsetails evolved in the Silurian and I have noticed that when the leaves of modern ferns die above ground in wetlands and uplands they burn well. In the spring in the Southeastern United States after a winter fire, the ferns quickly sprout back from beneath the ground with fresh new fronds. Not only does the fire remove the mulching caused by the old dead fronds, it provides new useable nutrients to the sprouting plant helping the plant grow stronger and better.
Fire in the Devonian
(419.2 – 358.9 million years)
The Devonian sees fire and fire adapted plants becoming widespread around the globe. At that time, there was the supercontinent of Gondwana in the south and the continent of Siberia in the north along with the small continent of Euramerica. [17] Wikipedia states:
“The Devonian period experienced the first significant adaptive radiation of terrestrial life. Since large vertebrate terrestrial herbivores had not yet appeared, free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents.” Devonian image [18] Landmass image [19]
“By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods also became well-established. Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the “Age of Fish".”
During the Middle Devonian, plants began to grow taller and larger. It was during this period that the
first trees evolved. [20] It was also at this time that small trees arose growing to about 6 feet high. A tree trunk with an attached crown was discovered in the state of New York (called Eospermatopteris) and was sized up to 8 meters. In the Late Devonian archaeopteris is the best well known tree and is possibly an ancestor of the conifers. This tree reached a height of 18 meters. By the end of the Devonian, the first seed plants had emerged.
In this article titled Newfound Fossils Reveal Secrets of World’s Oldest Forest [21] suggests that trees were already dropping their limbs to the ground providing habitat for animals. The Gilboa Forest dates to 385 million years and these forests were widespread around the world at this time. The article states, “And the trees, like modern palms, likely dropped their branches on a yearly or seasonal cycle, filling the forest floor with woody litter suitable for arthropods such as spiders and insects.”
The Cabbage Palm in the southeastern United States, like many other palms around the world having evolved from these early forests, are a very fire adapted species. The trunks are so fire tolerant that they can be almost burnt down by hot periodic fires and still survive. These palms have very flammable fronds that burn very hot, adapted to most likely burn out the competition from other evolving tree species. I suggest the reason these forests were so widespread is because of this very successful adaptive fire trait.
The above article also states, “Stein noted that these early trees played a major role in establishing Earth's first terrestrial ecosystems. “"Trees really dominate those kinds of environments they're found in. They really are the entire fabric in which an entire ecology fits in a terrestrial realm,"” he said.
Fire in the Carboniferous
(359.2 – 299.0 million years)
The Carboniferous began with vast forests already covering the continents and oxygen levels rose above levels not seen before or since. During the first part of the Carboniferous the coal beds were laid down in warm tropical and subtropical forests that provide much of our energy we use today. Arthropods (modern insects) became very prominent and grew to great size because the higher oxygen
levels. This was a time that the amphibians flourished feeding on insects, and sometimes the Carboniferous is called the age of amphibians and early reptiles. [22]
A minor extinction event occurred in the middle of the Carboniferous caused by a change in climate as continents collided becoming the supercontinent Pangaea. This caused cooling glaciation, and low sea level. I suspect this coming together of the continents also put species of plants and animals isolated on different continents into conflict with each other causing extinctions of less adaptable species.
This cooling and drying of the planet caused the tropical rainforest to collapse into fragments and the more arid lands saw frequent wildfires both of high intensity and low intensity partly created by high oxygen levels. Some scientists speculate that wildfires were of very high intensity because of the high oxygen levels. I and others suspect that the higher oxygen levels just led to more frequent less intense fires, as leaf litter caught fire quicker than it normally would. This was a time of great adaptation to fire by most species of plants and animals because fire was so frequent and intense, perhaps even more than anytime in earth’s history. Carboniferous fire image [23] Landmass image [24]
Fire in the Permian
(303.7 – 254.2 million years)
In the Permian the earth was dominated by the
single supercontinent called Pangaea and this
supercontinent was surrounded by a global ocean called Panthalassa. According to this Wikipedia entry:
“The extensive rainforests of the Carboniferous had disappeared, leaving behind vast regions of arid desert within the continental interior. Reptiles, who could better cope with these drier conditions, rose to dominance in lieu of their amphibian ancestors. The Permian Period (along with the Paleozoic Era) ended with the largest mass extinction in Earth’s history in which 90% of marine species and 70% of terrestrial species died out. It would take well into the Triassic for life to recover from this catastrophe.” [25]
This extinction was so severe that it is the only known extinction where insects were affected. The cause of this mass extinction is still being debated by scientists. Permian image [26] Landmass image [27] During the Permian many conifer groups, the ancestors or modern day families, spread across Pangaea. Very complex forests were present across Pangaea with a diversity of plant group species. The southern part of the continent saw extensive seed forest ferns and the ginkgos and cycads evolved during this period. Near the end of the Permian, the archosaurs evolved a group that would give rise to the dinosaurs of the following period.
It is significant that during this period the appearance of the first large herbivores and carnivores came into existence. The reason this is significant (as far as fire is concerned), is that like today, large herbivores are common in fire ecosystems where frequent less intense fires and even occasional catastrophic fires allow for vegetation to grow close to the ground within reach. Otherwise large trees will shade out most of the undergrowth needed to sustain these large herbivores.
Today we know that large herbivores assist fire to expand non-forest fire habitats such as savannas and grasslands by grazing down woody vegetation before it gets so tall that it shades out undergrowth as high brush and trees. The grasses and grasslands had not yet evolved, but we can expect that this environmental niche was already being filled by precursors to grass, as it was by the reptilian herbivore precursors to the mammalian herbivores. In fact, the early ancestors to mammals (the synapsida) were already evolving in the Permian.
Here we come to the end of a brief overview of fire in the Paleozoic and begin our overview of fire in the Mesozoic era starting with the Triassic period.
(303.7 – 254.2 million years)
In the Permian the earth was dominated by the
single supercontinent called Pangaea and this
supercontinent was surrounded by a global ocean called Panthalassa. According to this Wikipedia entry:
“The extensive rainforests of the Carboniferous had disappeared, leaving behind vast regions of arid desert within the continental interior. Reptiles, who could better cope with these drier conditions, rose to dominance in lieu of their amphibian ancestors. The Permian Period (along with the Paleozoic Era) ended with the largest mass extinction in Earth’s history in which 90% of marine species and 70% of terrestrial species died out. It would take well into the Triassic for life to recover from this catastrophe.” [25]
This extinction was so severe that it is the only known extinction where insects were affected. The cause of this mass extinction is still being debated by scientists. Permian image [26] Landmass image [27] During the Permian many conifer groups, the ancestors or modern day families, spread across Pangaea. Very complex forests were present across Pangaea with a diversity of plant group species. The southern part of the continent saw extensive seed forest ferns and the ginkgos and cycads evolved during this period. Near the end of the Permian, the archosaurs evolved a group that would give rise to the dinosaurs of the following period.
It is significant that during this period the appearance of the first large herbivores and carnivores came into existence. The reason this is significant (as far as fire is concerned), is that like today, large herbivores are common in fire ecosystems where frequent less intense fires and even occasional catastrophic fires allow for vegetation to grow close to the ground within reach. Otherwise large trees will shade out most of the undergrowth needed to sustain these large herbivores.
Today we know that large herbivores assist fire to expand non-forest fire habitats such as savannas and grasslands by grazing down woody vegetation before it gets so tall that it shades out undergrowth as high brush and trees. The grasses and grasslands had not yet evolved, but we can expect that this environmental niche was already being filled by precursors to grass, as it was by the reptilian herbivore precursors to the mammalian herbivores. In fact, the early ancestors to mammals (the synapsida) were already evolving in the Permian.
Here we come to the end of a brief overview of fire in the Paleozoic and begin our overview of fire in the Mesozoic era starting with the Triassic period.
Fire in the Triassic
(252 – 208.5 million years)
The Triassic is the first period in the Mesozoic era. Major extinction events marked the beginning and end of the Triassic. Wikipedia states:
“The Triassic began in the wake of the Permian-Triassic extinction event, which left the Earth’s biosphere impoverished; it would take well into the middle of the period for life to recover its former diversity. Therapsids and Archosaurs were the chief terrestrial vertebrates during this time.” Triassic image [28] Landmass image [29]
“A specialized subgroup of Archosaurs, dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic. The first true mammals, themselves a specialized subgroup of Therapsids also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who like the dinosaurs were a specialized subgroup of Archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north, and Gondwana to the south.”
“The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea’s interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, wiping out many groups and allowing dinosaurs to assume dominance in the Jurassic.” [30]
In the Triassic, the seed plants came to dominate the terrestrial flora. In the northern hemisphere of Pangaea, the conifers flourished. In the southern hemisphere, glossopteris (a seed fern) was the dominant southern hemisphere tree during the Early Triassic period. At the end of the Permian, oxygen levels plummeted and fire activity subsided. This activity coincided with the mother of all extinctions that produced a rarity of charcoal in the geologic record. This rarity of charcoal suggests that there was very low biomass throughout the Triassic.
With oxygen levels and biomass both low, we can expect that there was reduced fire activity during this period. However, it was not enough to stop the process of fire adaptation among plants and animals that had already become very extensive by this time. Fires would appear to be limited and contained until oxygen levels rose, with fire increasing exponentially in the late Jurassic through the Cretaceous, as evidenced by huge increases in fossil charcoal.
(252 – 208.5 million years)
The Triassic is the first period in the Mesozoic era. Major extinction events marked the beginning and end of the Triassic. Wikipedia states:
“The Triassic began in the wake of the Permian-Triassic extinction event, which left the Earth’s biosphere impoverished; it would take well into the middle of the period for life to recover its former diversity. Therapsids and Archosaurs were the chief terrestrial vertebrates during this time.” Triassic image [28] Landmass image [29]
“A specialized subgroup of Archosaurs, dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic. The first true mammals, themselves a specialized subgroup of Therapsids also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who like the dinosaurs were a specialized subgroup of Archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north, and Gondwana to the south.”
“The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea’s interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, wiping out many groups and allowing dinosaurs to assume dominance in the Jurassic.” [30]
In the Triassic, the seed plants came to dominate the terrestrial flora. In the northern hemisphere of Pangaea, the conifers flourished. In the southern hemisphere, glossopteris (a seed fern) was the dominant southern hemisphere tree during the Early Triassic period. At the end of the Permian, oxygen levels plummeted and fire activity subsided. This activity coincided with the mother of all extinctions that produced a rarity of charcoal in the geologic record. This rarity of charcoal suggests that there was very low biomass throughout the Triassic.
With oxygen levels and biomass both low, we can expect that there was reduced fire activity during this period. However, it was not enough to stop the process of fire adaptation among plants and animals that had already become very extensive by this time. Fires would appear to be limited and contained until oxygen levels rose, with fire increasing exponentially in the late Jurassic through the Cretaceous, as evidenced by huge increases in fossil charcoal.
Fire in the Jurassic
(208.5 – 152.1 million years)
As the Jurassic period began, the supercontinent Pangaea was rifting into the two landmasses, Laurasia to the north, and Gondwana to the south. This breaking apart of Pangaea created more coastlines and changed the climate from dry to humid with many arid deserts of the Triassic becoming lush
rainforests. During this period, the dinosaurs flourished and dominated other species such as the early mammals. This was also the period when the first birds appeared. The oceans were filled with marine reptiles such as ichthyosaurs and plesiosaurs. Pterosaurs were still the dominant flying vertebrates. Jurassic Image [31] Landmass image [32]
The conifers dominated the flora as they had during the Triassic with most large trees being conifers. The gymnosperms (the ancestors of modern conifers, cypress and pines), became very diverse in the Jurassic. The extinct Mesozoic conifer family (Cheirolepidiaceae) dominated low latitude vegetation as well as the bennettitale shrubs. Cycads, ginkgos and tree ferns were also common in these Jurassic forests. Ginkgos were common in the middle and higher latitudes in the Northern Hemisphere but rare in the Southern Hemisphere. [33]
Gymnosperms of the past, (like modern day pines, conifers, and cypress) are very fire adapted and are a product of high fire environments. Gymnosperms have resin that is an antimicrobial material that seals wounds from insects, but it is also very flammable. The following link on gymnosperms states:
“It is also flammable and thus it turns over the nutrients faster and clears the underbrush so that it
makes sure to have enough water available for survival by eliminating the competition. The gymnosperms do not burn due to their often 1 foot thick cork that is fire resistant and helps to insulate the phloem against freezing in the winter.” [34]
Some gymnosperms like today's redwoods release seeds after cool periodic fires while some pines have cones that only release seeds after a catastrophic fire. The cones of some pines explode like popcorn when heated and so disperse their seeds on the fire cleared ground. Here the young seedlings can take root because the competition has been burnt away. They also utilize the ash as fertilizer to grow fast and get a jump on the competition that will be sprouting back with their own fire strategies.
(208.5 – 152.1 million years)
As the Jurassic period began, the supercontinent Pangaea was rifting into the two landmasses, Laurasia to the north, and Gondwana to the south. This breaking apart of Pangaea created more coastlines and changed the climate from dry to humid with many arid deserts of the Triassic becoming lush
rainforests. During this period, the dinosaurs flourished and dominated other species such as the early mammals. This was also the period when the first birds appeared. The oceans were filled with marine reptiles such as ichthyosaurs and plesiosaurs. Pterosaurs were still the dominant flying vertebrates. Jurassic Image [31] Landmass image [32]
The conifers dominated the flora as they had during the Triassic with most large trees being conifers. The gymnosperms (the ancestors of modern conifers, cypress and pines), became very diverse in the Jurassic. The extinct Mesozoic conifer family (Cheirolepidiaceae) dominated low latitude vegetation as well as the bennettitale shrubs. Cycads, ginkgos and tree ferns were also common in these Jurassic forests. Ginkgos were common in the middle and higher latitudes in the Northern Hemisphere but rare in the Southern Hemisphere. [33]
Gymnosperms of the past, (like modern day pines, conifers, and cypress) are very fire adapted and are a product of high fire environments. Gymnosperms have resin that is an antimicrobial material that seals wounds from insects, but it is also very flammable. The following link on gymnosperms states:
“It is also flammable and thus it turns over the nutrients faster and clears the underbrush so that it
makes sure to have enough water available for survival by eliminating the competition. The gymnosperms do not burn due to their often 1 foot thick cork that is fire resistant and helps to insulate the phloem against freezing in the winter.” [34]
Some gymnosperms like today's redwoods release seeds after cool periodic fires while some pines have cones that only release seeds after a catastrophic fire. The cones of some pines explode like popcorn when heated and so disperse their seeds on the fire cleared ground. Here the young seedlings can take root because the competition has been burnt away. They also utilize the ash as fertilizer to grow fast and get a jump on the competition that will be sprouting back with their own fire strategies.
Fire in the Cretaceous
(152.1 - 72.1 million years)
The Cretaceous spanned about 79 million years and generally had a warm climate making for high sea levels and many numerous shallow seas. At this time new groups of mammals and birds appeared along with flowering plants. The flowering plants (angiosperms) according to DNA evidence had existed since the Permian, but it was during the Cretaceous that the angiosperms really began to dominate the gymnosperms. Most of these two groups were already very fire adapted from earlier times. The Cretaceous ended with a massive extinction that resulted in the loss of all the non-avian dinosaurs and the large marine reptiles. Cretaceous image [35] Landmass image [36]
It was during the Cretaceous that the breakup of Pangaea became almost complete, with only the continent of Australia still connected to Antarctica. Already Pangaea had broken into Laurasia in the north and Gondwana in the south, with North America pulling away from Eurasia in the Jurassic to become completely separate in the Cretaceous. South America split off from Africa, from which India, Australia and Antarctica were also separating, leaving India adrift in the Indian Ocean. When the Cretaceous ended, most of our present day continents were separated by large oceans such as the North and South Atlantic Ocean. [37]
This breakup of Pangaea was a very important development in the history of life and of fire. Plants and animals had competed together throughout the whole of Pangaea, but when the continent broke apart all these very advanced fire ecosystems became separated. They continued to evolve under more isolated conditions, but the basic structure of plant and animal species had pretty much become set. If one travels about the world one cannot but be impressed by how similar the trees, palms, pines and conifers all look as well as other plant and animal species.
We see very similar fire adaptations throughout all these now separated fire adapted ecosystems. In a sense, man over the past several hundred years has brought the continent of Pangaea back together again by transporting plants and animals back and forth across continents and thus putting separated ecosystems back into contact and competition with each other. It’s almost as if man himself became a land bridge between continents for better or for worse.
Today, the more adaptable species moving between continents are in competition with the more specialized less adaptable species. This is resulting in mass extinctions of plant and animal species that lose out in the process. In addition, man is altering the global climate helping more adaptable species, while at the same time destroying more specialized less adaptable species.
It’s becoming clear that all these mass and minor extinctions over geologic time mean that nature is intent on limiting or balancing excesses of over specialization and or generalization. This continuous resetting of this biological clock is pitting diversity against adaptability making for optimal survivability regardless of changing environmental conditions.
In the Cretaceous, even the polar regions were free of continental ice sheets, and the land was covered by forests and savannas. Dinosaurs were common in Antarctica even with its long winter night. Of greatest importance was that angiosperms (flowering plants) developed and thrived during the Cretaceous and today represent 80% of the known green plants now living. Encyclopedia Britannica states:
“The variety of forms found among angiosperms is greater than that of any other plant group. The size alone is quite remarkable, from the smallest individual flowering plant, probably the watermeal (Wolffia; Araceae) at less than 2 millimeters (0.08 inch), to one of the tallest angiosperms, Australia’s mountain ash tree (Eucalyptus regnans; Myrtaceae) at about 100 meters (330 feet).” [38] "Flowering plants in all their diversity form the bulk of the vegetation upon which animals feed. This includes the Grasses (Graminoids) that are usually herbaceous plants with narrow leaves growing from the base. This includes the true grasses as well as sedges and
rushes."
"Grasses became widespread during the latter part of the Cretaceous and fossilized dinosaur dung has been found with grasses related to modern rice and bamboo. Grasses are the most widespread plant type providing food and energy for all kinds of wildlife and organics. Grasses have adapted to conditions in lush rain forests, dry deserts, mountains and intertidal habitats." [39]
Most grasses have adapted to fire and need fire to exist and flourish. In addition, besides forests and savannas in our global ecosystems, we now have grasslands that have evolved from the fiery Cretaceous. There has always been a close association with large grazing herbivores and their predators with grasslands. Grazing pressures woody vegetation that combined with fire expands grasslands and grassland savannas way beyond what climate conditions and landscape would normally dictate.
During the Cretaceous grasslands evolved along with the grazing dinosaurs and when the dinosaurs were wiped out (except for the birds), grazing mammals evolved to fill the niche left behind by the loss of the dinosaurs. To a limited degree, some birds evolved into this niche of grazing on grasslands like geese and flightless birds.
It seems that a lot more fire research has been done on the Cretaceous than on previous periods. There does seem to be a bias by researchers not familiar with the role that light frequent fires play in the environment. They tend to play up catastrophic fires and downplay light regular periodic fires. I think this is just a carryover of the fire suppression culture of the past century. Catastrophic fire has been a part of fire ecosystems among some plant species usually in cooler climates where it takes longer for fuel accumulations to build up and burn, but over most of the earth light fire burns the ground cover clean before these fuel accumulations can build up to catastrophic proportions. The scientific paper called Cretaceous wildfires and their impact on the Earth system has this to say about the role of fire in the Cretaceous in its abstract:
“A comprehensive compilation of literature on global Cretaceous charcoal occurrences shows that from the Valanginian on throughout the Cretaceous, terrestrial sedimentary systems frequently preserve charcoal in abundance. This observation indicates that fires were widespread and frequent and that the Cretaceous can be considered a “high-fire” world.”
“This increased fire activity has been linked to elevated atmospheric oxygen concentrations, predicted as in excess of 21% throughout this period and 25% during some stages. This extensive wildfire activity would have affected the health, composition and structure of the vegetation and, through habitat loss, probably the fauna. For these reasons, fire activity should be taken into account in Cretaceous vegetation and climate models.” [40]
(152.1 - 72.1 million years)
The Cretaceous spanned about 79 million years and generally had a warm climate making for high sea levels and many numerous shallow seas. At this time new groups of mammals and birds appeared along with flowering plants. The flowering plants (angiosperms) according to DNA evidence had existed since the Permian, but it was during the Cretaceous that the angiosperms really began to dominate the gymnosperms. Most of these two groups were already very fire adapted from earlier times. The Cretaceous ended with a massive extinction that resulted in the loss of all the non-avian dinosaurs and the large marine reptiles. Cretaceous image [35] Landmass image [36]
It was during the Cretaceous that the breakup of Pangaea became almost complete, with only the continent of Australia still connected to Antarctica. Already Pangaea had broken into Laurasia in the north and Gondwana in the south, with North America pulling away from Eurasia in the Jurassic to become completely separate in the Cretaceous. South America split off from Africa, from which India, Australia and Antarctica were also separating, leaving India adrift in the Indian Ocean. When the Cretaceous ended, most of our present day continents were separated by large oceans such as the North and South Atlantic Ocean. [37]
This breakup of Pangaea was a very important development in the history of life and of fire. Plants and animals had competed together throughout the whole of Pangaea, but when the continent broke apart all these very advanced fire ecosystems became separated. They continued to evolve under more isolated conditions, but the basic structure of plant and animal species had pretty much become set. If one travels about the world one cannot but be impressed by how similar the trees, palms, pines and conifers all look as well as other plant and animal species.
We see very similar fire adaptations throughout all these now separated fire adapted ecosystems. In a sense, man over the past several hundred years has brought the continent of Pangaea back together again by transporting plants and animals back and forth across continents and thus putting separated ecosystems back into contact and competition with each other. It’s almost as if man himself became a land bridge between continents for better or for worse.
Today, the more adaptable species moving between continents are in competition with the more specialized less adaptable species. This is resulting in mass extinctions of plant and animal species that lose out in the process. In addition, man is altering the global climate helping more adaptable species, while at the same time destroying more specialized less adaptable species.
It’s becoming clear that all these mass and minor extinctions over geologic time mean that nature is intent on limiting or balancing excesses of over specialization and or generalization. This continuous resetting of this biological clock is pitting diversity against adaptability making for optimal survivability regardless of changing environmental conditions.
In the Cretaceous, even the polar regions were free of continental ice sheets, and the land was covered by forests and savannas. Dinosaurs were common in Antarctica even with its long winter night. Of greatest importance was that angiosperms (flowering plants) developed and thrived during the Cretaceous and today represent 80% of the known green plants now living. Encyclopedia Britannica states:
“The variety of forms found among angiosperms is greater than that of any other plant group. The size alone is quite remarkable, from the smallest individual flowering plant, probably the watermeal (Wolffia; Araceae) at less than 2 millimeters (0.08 inch), to one of the tallest angiosperms, Australia’s mountain ash tree (Eucalyptus regnans; Myrtaceae) at about 100 meters (330 feet).” [38] "Flowering plants in all their diversity form the bulk of the vegetation upon which animals feed. This includes the Grasses (Graminoids) that are usually herbaceous plants with narrow leaves growing from the base. This includes the true grasses as well as sedges and
rushes."
"Grasses became widespread during the latter part of the Cretaceous and fossilized dinosaur dung has been found with grasses related to modern rice and bamboo. Grasses are the most widespread plant type providing food and energy for all kinds of wildlife and organics. Grasses have adapted to conditions in lush rain forests, dry deserts, mountains and intertidal habitats." [39]
Most grasses have adapted to fire and need fire to exist and flourish. In addition, besides forests and savannas in our global ecosystems, we now have grasslands that have evolved from the fiery Cretaceous. There has always been a close association with large grazing herbivores and their predators with grasslands. Grazing pressures woody vegetation that combined with fire expands grasslands and grassland savannas way beyond what climate conditions and landscape would normally dictate.
During the Cretaceous grasslands evolved along with the grazing dinosaurs and when the dinosaurs were wiped out (except for the birds), grazing mammals evolved to fill the niche left behind by the loss of the dinosaurs. To a limited degree, some birds evolved into this niche of grazing on grasslands like geese and flightless birds.
It seems that a lot more fire research has been done on the Cretaceous than on previous periods. There does seem to be a bias by researchers not familiar with the role that light frequent fires play in the environment. They tend to play up catastrophic fires and downplay light regular periodic fires. I think this is just a carryover of the fire suppression culture of the past century. Catastrophic fire has been a part of fire ecosystems among some plant species usually in cooler climates where it takes longer for fuel accumulations to build up and burn, but over most of the earth light fire burns the ground cover clean before these fuel accumulations can build up to catastrophic proportions. The scientific paper called Cretaceous wildfires and their impact on the Earth system has this to say about the role of fire in the Cretaceous in its abstract:
“A comprehensive compilation of literature on global Cretaceous charcoal occurrences shows that from the Valanginian on throughout the Cretaceous, terrestrial sedimentary systems frequently preserve charcoal in abundance. This observation indicates that fires were widespread and frequent and that the Cretaceous can be considered a “high-fire” world.”
“This increased fire activity has been linked to elevated atmospheric oxygen concentrations, predicted as in excess of 21% throughout this period and 25% during some stages. This extensive wildfire activity would have affected the health, composition and structure of the vegetation and, through habitat loss, probably the fauna. For these reasons, fire activity should be taken into account in Cretaceous vegetation and climate models.” [40]
Cenozoic Era
(72.1 million – 11.700 thousand years)
While the end of the Cretaceous period and the beginning of the Cenozoic Era was marked by mass extinctions, it allowed mammals a chance to evolve into the niches that dinosaurs had left. In the plant kingdom regardless of what happened to individual species, the gymnosperms (conifers, pines and cypress), the angiosperms (flowering plants) continued to thrive and flourish evolving to
where they are today. It amazes me that there exists today so many types of plants that are changed little from their ancestors from that time plants first colonized the land. Cenozoic image [41]
Landmass image [42]
In the Paleogene the (first period of the Cenozoic Era), large grassy plains came into existence in the Eocene (an early division of the Paleogene). The Evolution of Plants article has this to say:
“Grass has the special quality of being more resistant to grazing than other angiosperms. Ancient horses lived in the jungle, but later on new horse species began to set out for more open spaces and they started to eat grass. Probably the large grassy plains developed by co-evolution of grazing animals and grass. This means that there was in interaction between the grazing animals and the grass: the animals ate the grass, the grass became adapted for the sake of survival, the animals adapted in their turn to innovation of the grass, and so on.” [43]
As I have stated previously, fire was another prime factor in grassland development as it has been previously in both forest and savannas. The author of the Evolution of Plants article also made the point that to fully understand angiosperms, and I assume gymnosperms as well, that an extensive knowledge of the now living flora is necessary because the fossils can be compared to their living relatives. According to this author. the average lifespan of a species is only about 6 million years. I guess where one divides the end of one species and another begins is a bit subjective.
The species from a few million years ago are therefore very similar to the plants we have today and so for the ecosystems as well. In this last part of the Cenozoic Era, the ancestors of man come into the
fire and ecosystem equation. We shall continue the discussion of this in the next chapter (Fire and Man), beginning with the hominids several million years ago. Late Cenozoic Image [44]
(72.1 million – 11.700 thousand years)
While the end of the Cretaceous period and the beginning of the Cenozoic Era was marked by mass extinctions, it allowed mammals a chance to evolve into the niches that dinosaurs had left. In the plant kingdom regardless of what happened to individual species, the gymnosperms (conifers, pines and cypress), the angiosperms (flowering plants) continued to thrive and flourish evolving to
where they are today. It amazes me that there exists today so many types of plants that are changed little from their ancestors from that time plants first colonized the land. Cenozoic image [41]
Landmass image [42]
In the Paleogene the (first period of the Cenozoic Era), large grassy plains came into existence in the Eocene (an early division of the Paleogene). The Evolution of Plants article has this to say:
“Grass has the special quality of being more resistant to grazing than other angiosperms. Ancient horses lived in the jungle, but later on new horse species began to set out for more open spaces and they started to eat grass. Probably the large grassy plains developed by co-evolution of grazing animals and grass. This means that there was in interaction between the grazing animals and the grass: the animals ate the grass, the grass became adapted for the sake of survival, the animals adapted in their turn to innovation of the grass, and so on.” [43]
As I have stated previously, fire was another prime factor in grassland development as it has been previously in both forest and savannas. The author of the Evolution of Plants article also made the point that to fully understand angiosperms, and I assume gymnosperms as well, that an extensive knowledge of the now living flora is necessary because the fossils can be compared to their living relatives. According to this author. the average lifespan of a species is only about 6 million years. I guess where one divides the end of one species and another begins is a bit subjective.
The species from a few million years ago are therefore very similar to the plants we have today and so for the ecosystems as well. In this last part of the Cenozoic Era, the ancestors of man come into the
fire and ecosystem equation. We shall continue the discussion of this in the next chapter (Fire and Man), beginning with the hominids several million years ago. Late Cenozoic Image [44]