Mass extinctions are catastrophic events in the history of life on Earth, where significant species loss occurs in a relatively short period of time. Five mass extinctions have been recorded in Earth’s history, and the most recent occurred about 66 million years ago, at the end of the Cretaceous period.
The five mass extinctions are described below:
Mass extinction of the Orthovichic-Silurian
The Ordovician-Silurian mass extinction was a catastrophic event that occurred about 444 million years ago, during the transition from the Ordovician to the Silurian period. This extinction was the first of five major mass extinctions in Earth’s history.
It is estimated that around 85% of marine species went extinct during this event, representing the greatest loss of biodiversity in Earth’s history. Possible causes of this extinction include changes in oxygen and carbon dioxide levels in the oceans, the expansion of anoxic zones on the sea floor, and global cooling.
During the Ordovician, the continents were united into a single supercontinent called Gondwana and most life on Earth was in the oceans. The Ordovician-Silurian mass extinction had a significant impact on marine biodiversity, and many groups of marine organisms, such as trilobites, brachiopods and graptolites, were affected. Although some groups of organisms, such as corals and molluscs, survived the extinction, marine biodiversity was never the same after this event.
Devonian mass extinction
The Devonian mass extinction was a catastrophic event that occurred approximately 375 million years ago, during the transition from the Devonian to the Carboniferous period. This extinction mainly affected marine organisms, although some terrestrial groups were also affected.
It is estimated that about 70% of marine species became extinct during this event, including many corals and brachiopods. Possible causes of this extinction include declining oxygen levels in the oceans, acidification of seawater, and competition for resources due to the evolution of new species.
Even though marine biodiversity recovered quickly after the extinction, the event had a lasting impact on the evolution of life on Earth. During the Devonian, there was a major diversification of marine organisms, including fish and tetrapods, the first animals to colonize land. The Devonian mass extinction had a significant impact on the evolution of these groups and thus on the evolution of life in general.
Permian-Triassic mass extinction
The Permian-Triassic mass extinction, also known as the Great Extinction, was a catastrophic event that occurred about 252 million years ago, during the transition from the Permian to the Triassic period. This was the worst mass extinction in Earth’s history, in which it is estimated that around 95% of all species went extinct, both on land and at sea.
Possible causes of this extinction include intense volcanic activity that released large amounts of carbon dioxide and other gases into the atmosphere, causing global climate change and ocean acidification. In addition, the formation of a supercontinent called Pangaea may have altered ocean circulation patterns and global climate.
The Permian-Triassic mass extinction had a significant impact on the evolution of life on Earth. Many groups of organisms, including trilobites, brachiopods and corals, disappeared completely, while others, such as reptiles and mammals, evolved from the survivors.
The recovery of biodiversity after this extinction was slow and took millions of years. However, the Permian-Triassic mass extinction also allowed the evolution of new groups of organisms that would dominate life on Earth during the following geological periods.
Triassic-Jurassic mass extinction
The Triassic-Jurassic mass extinction was a catastrophic event that occurred about 201 million years ago, during the transition from the Triassic to the Jurassic period. Although not as severe as the Great Permian-Triassic Extinction, it is still estimated that about 50% of marine and terrestrial species went extinct.
Possible causes of this extinction include intense volcanic activity that released large amounts of greenhouse gases into the atmosphere, causing global climate change. In addition, the opening of the Atlantic Ocean may have altered ocean circulation patterns and global climate.
The Triassic-Jurassic mass extinction had a significant impact on the evolution of life on Earth. Many groups of organisms, including marine reptiles and brachiopods, disappeared, while others, such as dinosaurs, survived and evolved to become the largest and most diverse land animals during the Jurassic.
The recovery of biodiversity after this extinction was relatively rapid and allowed the evolution of new groups of organisms that would dominate life on Earth during the following geological periods.
Cretaceous-Paleogene mass extinction
The Cretaceous-Paleogene mass extinction, also known as the extinction of the dinosaurs, was a catastrophic event that occurred about 66 million years ago, during the transition from the Cretaceous to the Paleogene period. This extinction mainly affected terrestrial organisms, particularly non-avian dinosaurs and many groups of plants.
The main cause of this extinction is widely accepted as the impact of an asteroid about 10 km in diameter on the Yucatan Peninsula in what is now Mexico, which caused the release of large amounts of dust and gases into the atmosphere, and caused a global nuclear winter that lasted several years. In addition, it has also been suggested that intense volcanic activity in India may have contributed to the extinction by releasing large amounts of greenhouse gases into the atmosphere, causing global climate change.
The Cretaceous-Paleogene mass extinction had a significant impact on the evolution of life on Earth. The demise of dinosaurs allowed mammals to evolve and diversify, leading to the emergence of modern mammals. In addition, the extinction also allowed flying reptiles, such as pterosaurs, to disappear, allowing the evolution of the first birds.
The recovery of biodiversity after this extinction was relatively rapid compared to other mass extinctions, and allowed the evolution of new groups of organisms that would dominate life on Earth during the following geological periods.
