Five Mass Extinction Events

Introduction

In the fifth article from The Theory of Evolution series we settled, that extinction is a natural evolutionary process. However, sometimes it happens very fast, killing most of existing life. There were five mass extinction events during the history of Earth. Despite the catastrophes, life always found its way back, sometimes in very similar form.  Though those events may seem tragic, without them we would never exist, moreover the whole life on Earth would be completely different than it is today. Let’s talk about five mass extinction events.

The Ordovican-Silurian extinction

Almost 440 million years ago, life flourished. First vertebrates, and later first fish, and corals, appeared during the Ordovican radiation. Moreover, some plants left its marine ecosystems and moved to Godwana. As great as that land expansion may seem, it didn’t end well. The ancestors of modern mosses absorbed CO2 from the atmosphere and, due to secreting organic acids, dissolved the rocks they lived on. This caused a lot of minerals going into the ocean, which led to massive algal blooms. Moreover, algae absorbed more CO2, due to activity of small organisms large areas without oxygen occurred. All in all, this caused extinction of 60% marine organisms, and the dropping level of greenhouse gases allowed ice caps to form. Afterwards, one of the greatest ice ages in the history of our planet happened.

Related: How did life begin on Earth?

The first mass extinction is connected with very long ice age
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The late Devonian extinction

After years of ice age, life found its way back in a very similar way. Fishes, later trilobites, and land plants came back, and kept on developing. Tiktaalik was a kind of highly developed fish, with features similar to today’s four-legged animals. Plants reached almost 30 m height, which might cause the destabilization in climate and led to another extinction event, in similar way the first one did. In contrast, another theory suggests  that the big climate change was caused by plate tectonics movement, or by an asteroid. Whatever the cause was, it wiped out 50% of all genera.  Moreover, vertebrates did not appear for the next 10 million years.

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After years of ice age, highly developed fish appeared
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The largest mass extinction

The third event marked the border between the Permian and Triassic periods. Marine invertebrates reached their lowest point since the Ordovician, some groups of aquatic vertebrates –first jawed fishes and jawed fishes with significant armor- were eliminated forever. On-land life also suffered- reptiles, first mammal-like reptiles, and almost 90% of insects gone extinct. All in all 96% of life extinct during that event. You may wonder, what caused the terrible Great Dying. It was probably a huge volcanic eruption, which warmed the Earth and acid the oceans, therefore leading to drastic climate changes. Another hypotheses suggest that it may be increasing population of methane-producing microbes or some sort of alteration in carbon cycle, which caused increase in water temperature and acidity.

Also Read: What will happen if the Yellowstone Supervolcano erupts today?

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During the Great Dying 96% of life was wiped out
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The Triassic-Jurassic mass extinction

Only 50 million years after the Great Dying, the next mass extinction event took place.  It was only 10,000 years after Pangaea broke apart and vacated ecological niches allowed dinosaurs to reign the Earth in the next period. During the end Triassic extinction fish managed to survive, same with most marine reptiles. In contrast, terrestrial life suffered a lot more. 42% of terrestrial tetrapods went extinct (such as amphibians and reptiles). The Edwin Colbert’s study shows how dinosaurs filled the niches other organisms left empty. The cause of this event remains an uncertain thing. Some scientists suggest that due to increasing plate tectonics movement and Pangaea braking apart, there was a huge climate change and increases in volcanic activity.

Other studies point out that, due to increase in CO2 level polar ice melted, which liberated great amounts of methane, trapped in under sea ice. Therefore, there was a significant increase in temperature and 76% of species went extinct.

The niches emptied after end Triassic extinction allowed dinosaurs to rule the Earth
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Most recent extinction

As we all know, dinosaurs didn’t last either. The Cretaceous–Paleogene extinction event happened 65 million years ago and it is definitely the most popular one among all mass extinction events.  The combination of volcanic activity, asteroid impact, and climate change killed 75% of species. The only lines of archosaurs  (group that contains reptiles, dinosaurs, and birds) evolved to what we know today as crocodilians and modern birds. Moreover, marine life also suffered, only 13% of plankton survived, free-swimming ammonoids known today as common fossils, extinct completely, so did other classes of marine invertebrates. Plants, amphibians, and mammals survived with minor loses, which furthermore allowed them to evolve to forms we know today. The most recent mass extinction event led to development of mammals, who took over the Earth. However, it remains controversial how this very sensitive to habitat organisms survived better than way more plastic dinosaurs.

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The extinction of dinosaurs is still a mystery case
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Related: All the articles of Theory of Evolution series

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