What We Learned from the Major Extinction Events on Earth
written by: ciel s cantoria•edited by: Sarah Malburg•updated: 5/12/2010
Mass extinctions entail catastrophe and loss of lives that exist in different habitats and on a global scale.
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According to researchers and scientists from Princeton and Bristol Universities, all the indications of another mass extinction are present. Based on the results of their studies of geological changes, there is strong evidence that global warming and changes in global climate had caused the five mass extinctions 439 million years ago.
Below is a brief accounting about each of the five mass extinctions and the geological changes that happened prior to their occurrences. Rather than be confused and be kept in the dark about what scientists think had happened, it would help us to understand the mass extinction occurrences that a lot of people have been recently debating on.
(Kindly click on the image on your left for a larger view of the mass extinction timelines.)
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Mass Extinction 1- Ordovician-Silurian Extinction
The first of the mass extinctions happened 439 million years ago during the Ordovician-Silurian period. This was the initial phase of the pre-historic era when most of the land masses were still one major continent, which scientists named as Gondwana. Accordingly, it drifted for some time until it settled in the South Pole. The movement of several bodies of water later separated these land masses to form the continents we now know of as Africa, South America, Australia, Antarctica and North America, but was completed only in the later pre-historic periods. North America was said to be the first to separate.
During the earlier part of this period, the Earth’s climate was said to be warm and life on Earth was mostly marine creatures and underwater primitive plants. Marine life was chiefly squid-like and tentacled-mollusks while the reefs abounded with large sea lilies that looked like feathery arms waving in the deep sea currents. Whatever life there was on Earth, however, was cut short when sea levels began and continued to rise; until Gondwana finally settled in the South Pole and started forming massive glaciers due to temperatures changes. Hence, the Earth existed in twenty million years of Ice Age, which resulted in the first mass extinction. This catastorphe destroyed about 60% of all existing life forms.
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Mass Extinction 2- Devonian Extinction
The second of the five mass extinctions took place 364 million years ago or roughly about 75 million years after the Ordovician-Silurian period. The super continent Gondwana was able to dislodge itself in the South Pole area and veered towards the north. However, parts of its landmass also separated to form another continent which will become North America, Northern Europe, Russia and Greenland in the distant future. Geologically, red colored sediments appeared when North America and Europe collided against each other and most of these sediments were first found in Devon, England. Hence, the period was aptly named that of Devonian.
This era was also known to be the Age of Fishes, since marine life spawned numerous varieties of fish. They included species that had powerful jaws and blade-like plates which served as teeth. Based on fossil studies, there were quite a number of ferocious species that measured up to 33 feet and seemed to have the appearance of having heavy protective armor and rounded shields. This was also the period where fossils unearthed from the red rocks in Devon, showed signs that marine life had started to seek life on land. The fossils of the first amphibians had crocodile-like heads, bony fins and short legs. These species were said to have survived up to the last of the mass extinction which was during the Cretaceous period.
It appeared that the red sediments also encouraged the growth of stemmed plants that had woody structures which grew from 30 feet to 100 feet in height. Researches were able to collect data to indicate that the first forest was formed before the Devonian period ended. The asteroid or comet impact was also suggested as the cause of the 2nd mass extinction but evidence shows that most of the victims were marine life; 70% was eradicated. The reef-building communities also disappeared.
The most feasible explanation scientists could offer is that the emergence of plant life reduced the levels of greenhouse gases in the atmosphere, particularly carbon dioxide. This caused the climate to experience global cooling while glaciers continued to form in Gondwana.
Please proceed to the next page for the continuation of the 5 mass extinctions.
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Learn about the geological changes that took place during the Permian Triassic and End Triassic periods and learn the reasons why these major mass extinctions happened.
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Mass Extinction 3 –Permian Triassic Extinction
The third of the major mass extinctions took place 251 million years ago and roughly about 113 million years after the Devonian period. This period saw the emergence of another super continent which was called Pangea, in the northern area. It was said to be so huge that its climates were quite extreme and varied. Climates were characterized by intense heat and seasonal fluctuations between wet and dry patterns. This condition brought about the conifers, the seed ferns and other plants that had the ability to withstand droughts.
During this Permian Triassic period, the remaining reptiles moved in to new environments until they became adapted to the desert-like habitats. Initially cold-blooded, they eventually became warm-blooded reptiles in a new environment that provided them with different forms of sustenance. There were flesh-eating carnivores as well as herbivores, but most of them grew to be huge and weighed more than a ton. These new animals are obviously the dinosaurs we all know of and became the dominant life form on land. The seas on the other hand, produced new fish species that were bony and had fan-like fins and heavy scales. During the latter part of the Permian era, there were smaller species of warm-blooded animals covered with hair that emerged. This was said to be the species from where mammals would arise.
However, the worst mass extinction took place in this Permian Triassic period, which wiped out 70% of the land animals and about 90% of marine life. In eliminating the asteroid/comet theory, scientists and scholars presented series of volcanic eruptions as the root causes of the extinction. The continuous flow of hot flaming lava caused large quantities of fumes, ashes and debris to rise up in the air and became part of the atmosphere. This development blocked out the sun’s radiations and prevented plants from their food production processes which involved photosynthesis.
The food chain was thus broken and soon the Earth’s inhabitants slowly went into extinction as food sources eventually disappeared. Due to the great number of extinct involved, scientists also considered the possibility that some species could not withstand the extreme temperature brought about by sudden global warming, which also triggered the rising of methane gas from under the ocean’s sea bed.
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Mass Extinction 4- End Triassic Extinction
The 4th major mass extinction came about roughly 35 million years after the Permian Triassic mass extinction, which was 214 million years ago from today. The Triassic era was said to be the darkest and most desolate time in the Earth’s history. It was characterized by continuous occurrences of volcanic eruptions, climate changes and possible collisions with asteroids and comets.
The newly formed supercontinent Pangaea had begun to break down as the tectonic forces started to split its landmasses while positioned in the Earth’s equator. The North and South Poles became totally ice-free at this time. Marine life had mostly coiled-shells, mollusks, sea-urchins and phytoplanktons as the remaining life forms that survived the Permian mass extinction. On land, amphibians like frogs, turtles, crocodiles, salamanders and snakes slithered in and out of the water. Perhaps due to their large size and domination of land, sea and air, dinosaurs still survived and evolved like the 27.5 foot-long herbivore called Plateosaurus. Accordingly, the dinosaurs lived long and flourished up to the Jurassic period.
But still, mass extinction also took place, wiping out 52 percent of the remaining marine life as an end to the Permian period.
Please proceed to the next page for the 5th mass extinction.
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Cretaceous Tertiary extinction is the fifth and last of the 5 mass extinctions known to have taken place in history. This was the time when even dinosaurs were pushed into non-existence.
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Mass Extinction 5- Cretaceous-Tertiary Extinction
Cretaceous refers to the geological characteristics more than 65 million years ago. There is a gap of about 149 years since the 4th mass extinction that ended the Triassic period. During this time, geological changes of the Earths’ physical surface included the surfacing of far-reaching beds of chalks. The Earth’s large mass of land was still in the process of breaking up into continents. Before the end of this period, the bodies of water known today as the Atlantic Ocean widened and completed the breaking down of the supercontinents. This brought forth the continents of Australia, Antarctica, Africa and South America, but they were still not in the same position they are presently in. India and Madagascar were still parts of Africa during this period.
The climate during the Cretaceous era was said to be warm and the Polar Regions still had no permanent ice. The intense warmth was linked to the massive lava deposits in the area known as Deccan Trap, found in the region known today as India. During the Cretaceous period, the land was still dominated by dinosaurs; although marine animals also thrived.
The last of the 5 mass extinctions, the Cretaceous mass extinction, was supposed to have been caused by a comet or asteroid that hit Mexico’s Yucatan Peninsula which became buried beneath the Gulf of Mexico. The evidence that supports this theory was the indentation it made upon impact. Today, said indentation is called the Chicxulub crater and measures about 112 miles wide. The intensity of the impact created by a huge heavenly body expelled particles that rose into the air and soared into the atmosphere, which reached every corner of the Earth. As a result, the Earth did not receive adequate solar radiation for quite some time, which disrupted the Earth’s ecology. This subsequently caused the natural food chain to collapse and led to the fifth mass extinction.
Recent studies by scholars and scientists have replaced the asteroid/comet theory with the same volcanic eruption theories in the previous periods. The Deccan Traps located in the Indian area, was said to release floods of basalt liquid lava. Basalt is characterized by gas discharges that produced fountains of fire and incandescent lava. Hence, the occurrence of atmospheric changes that brought global warming and climate change. This caused the greatest mass extinction of all, where 70% of the Earth’s inhabitants including the dinosaurs were pushed into extinction.
By sorting out all of this information, many are inclined to believe the theory about volcanic eruptions as the more logical explanation. The possibility of asteroids and comets hitting the Earth in the 5 mass extinctions are possibly true but doubtful to have created a catastrophic impact. Most of the meteorites found on the Earth’s surface were not large enough to create a catastrophe that could affect the atmosphere. Studies show that their speed decelerates once they enter the Earth’s atmospheric layers.
What is frightening of course, is the similarity of the scenarios in the 5 mass extinctions to what is actually happening today. Mankind may have sped up global warming with their activities but everything is still at an unpredictable stage. Perhaps, we should also take into mind a religious tenet in relation to anticipated mass extinctions. All we need to be is prepared, since we will have no way of knowing when it will happen. “It will come like a thief in the night".