Mass Extinction Events

An extinction event, also known as a mass extinction or biotic crisis, is a sudden and significant decrease in the diversity of life on Earth. It is characterized by a rapid increase in extinction rates and a decline in the number of species. This can occur when there is a significant disruption to the environment, such as a massive asteroid impact, volcanic eruptions, or a change in climate, that makes it difficult for many species to survive.

Throughout Earth's history, there have been many mass extinctions, with estimates ranging from 5 to over 20. These events have occurred at different times and have had varying levels of impact on the planet's ecosystems.

In 1982, scientists Jack Sepkoski and David M. Raup identified five major mass extinctions in the Phanerozoic Eon (the current geological era), which they called the "Big Five". These events occurred:

During the Ordovician-Silurian extinction event (443-485 million years ago), which wiped out around 85% of all species.
During the Late Devonian extinction event (375-360 million years ago), which saw the loss of around 75% of all species.
During the End-Permian mass extinction event (252 million years ago), which was the most severe mass extinction event in Earth's history, resulting in the loss of around 96% of all marine species and 70% of all terrestrial species.
During the Triassic-Jurassic extinction event (200 million years ago), which saw the loss of around 80% of all species.
During the Cretaceous-Paleogene extinction event (65 million years ago), which resulted in the loss of around 75% of all species and is famous for being the event that led to the extinction of dinosaurs.

However, it's now believed that these events are not distinct "big five" but rather part of a larger continuum of extinction events. The "Big Five" were originally identified as outliers on a general trend of decreasing extinction rates during the Phanerozoic Eon, but as more stringent statistical tests have been applied to the accumulating data, it has been established that there have been many more mass extinctions throughout Earth's history.

In addition to these major mass extinctions, there were also likely mass extinctions of microbial life earlier in Earth's history. One such event is thought to have occurred during the Oxygen Catastrophe, which occurred around 2.7 billion years ago and saw the development of oxygen in the Earth's atmosphere. This event had a significant impact on the evolution of life on Earth.

Another mass extinction event is thought to have occurred before the Cambrian explosion, which was a period of rapid diversification of life on Earth around 541 million years ago. This event is believed to have wiped out many early life forms and paved the way for the development of more complex life forms.

Overall, mass extinctions are a natural part of Earth's history, and they have played a significant role in shaping the evolution of life on our planet.

Ordovician-Silurian Extinction

The Late Ordovician mass extinction (LOME) occurred around 445 million years ago and is considered the second-largest mass extinction event in Earth's history. It wiped out 49-60% of marine genera and nearly 85% of marine species. The extinction event was global and affected all major taxonomic groups, including brachiopods, bryozoans, conodonts, trilobites, echinoderms, corals, bivalves, and graptolites. The extinction occurred in two distinct pulses, with the first pulse occurring at the beginning of the Hirnantian stage due to the expansion of a glaciation that cooled the Earth and caused habitat loss for many organisms. The second pulse occurred later in the Hirnantian stage as the glaciation receded and was associated with intense anoxia and euxinia. Some researchers have proposed a third pulse of extinction during the early Rhuddanian stage, but this is not universally accepted. The extinction event did not produce major changes to ecosystem structures or lead to any particular morphological innovations. Diversity gradually recovered to pre-extinction levels over the first 5 million years of the Silurian period. Read more...

Late Devonian Extinction

The Late Devonian extinction was a mass extinction event that occurred around 372 million years ago, during the transition from the Frasnian to the Famennian stage of the Devonian period. It is considered one of the five largest mass extinction events in Earth's history. The extinction event was characterized by a significant loss of biodiversity, with 19% of all families and 50% of all genera becoming extinct. The event affected marine life, with hard-hit groups including brachiopods, trilobites, and reef-building organisms.

The causes of the extinction are still unclear, but leading hypotheses include changes in sea level and ocean anoxia, possibly triggered by global cooling or oceanic volcanism. Some scientists have also suggested that the impact of a comet or another extraterrestrial body may have played a role. The extinction event was accompanied by widespread oceanic anoxia, which allowed for the preservation of organic matter and has led to the formation of oil-rich rocks in places like Canada and the United States.

The extinction event had a significant impact on the evolution of life on Earth, with many species disappearing forever. The event also had a lasting impact on the Earth's ecosystems, leading to changes in the composition of marine life and paving the way for the evolution of new species. Read more...

Permian-Triassic Extinction Event

The Permian-Triassic extinction event, also known as the "Great Dying", was a catastrophic event that occurred around 251.9 million years ago. It is considered the most severe mass extinction event in Earth's history, with a staggering 57% of biological families, 83% of genera, and 81% of marine species becoming extinct. The impact was even more severe on terrestrial vertebrates, with 70% of species disappearing. This event is also known to be the greatest known mass extinction of insects.

The cause of this extinction event is still debated among scientists, but the majority of evidence suggests that it was primarily caused by massive flood basalt volcanic eruptions in Siberia. These eruptions released enormous amounts of sulfur dioxide and carbon dioxide into the atmosphere, leading to a range of devastating effects. The oceans became oxygen-starved, or euxinic, and the elevated levels of carbon dioxide resulted in a significant increase in global temperatures. The oceans also became acidified, making it difficult for many marine organisms to survive.

The eruption of these volcanoes also released large amounts of carbon dioxide into the atmosphere, causing a rapid increase in levels from around 400 parts per million to 2,500 parts per million. This is equivalent to releasing approximately 3,900 to 12,000 gigatonnes of carbon into the ocean-atmosphere system. Several other contributing factors have been proposed, including the emission of methane from the burning of oil and coal deposits, the release of methane from gasification and novel microorganisms nourished by minerals dispersed in the eruptions, and an extraterrestrial impact that destroyed the ozone layer and exposed the Earth to increased solar radiation. Read more...

Triassic-Jurassic Extinction Event

The Triassic-Jurassic extinction event, which occurred 201.4 million years ago, marked a significant turning point in the history of life on Earth. It is one of the five most significant extinction events in the Phanerozoic eon, and it had a profound impact on both life on land and in the oceans. In the oceans, 23-34% of marine genera went extinct, including the entire class of conodonts. On land, most archosauromorphs, including previously abundant groups such as aetosaurs and rauisuchids, became extinct.

However, some groups were able to survive and even thrive in the aftermath of the extinction event. Plants, crocodylomorphs, dinosaurs, pterosaurs, and mammals were relatively unaffected, and they went on to dominate the Earth's landscapes for millions of years to come. In fact, the extinction event allowed these surviving groups to become dominant land animals for the next 135 million years.

Despite the severity of the extinction event, statistical analysis suggests that it was not caused by an increase in extinctions, but rather by a decrease in speciation. The event was likely caused by the start of volcanic eruptions in the Central Atlantic Magmatic Province, which released large amounts of carbon dioxide into the atmosphere, inducing global warming and ocean acidification. The extinction event also resulted in a pronounced turnover in plant spores and a collapse of coral reef communities, indicating an ecological catastrophe. Read more...

Cretaceous-Paleogene Extinction Event

The K-Pg extinction event, which occurred 66 million years ago, marked the end of the Cretaceous period and the Mesozoic era, and the beginning of the Cenozoic era. This sudden and massive extinction event wiped out approximately 75% of all plant and animal species on Earth, making it one of the most significant events in the history of life on our planet.

The event caused the extinction of all non-avian dinosaurs, as well as many other terrestrial species, including mammals, birds, lizards, insects, and plants. In the oceans, the extinction killed off many species of fish, sharks, mollusks, and plankton. The exact cause of this extinction event is still debated among scientists, but most researchers agree that it was likely caused by the impact of a massive asteroid 10-15 km wide.

The asteroid impact hypothesis was supported by the discovery of the Chicxulub crater in the 1990s, which provided evidence that the K-Pg boundary clay was debris from an asteroid impact. Other factors that may have contributed to the extinction include volcanic eruptions, climate change, and sea level change. However, recent studies suggest that the asteroid impact was the primary cause of the extinction, and that volcanic eruptions may have played a smaller role.