Cause of First Mass Extinction

A paper published recently has come up with a new reason behind the first mass extinction, also known as the Late Ordovician mass extinction.

Species Extinction

·       Extinction is a part of life, and animals and plants disappear all the time. About 98% of all the organisms that have ever existed on our planet are now extinct.

·       When a species goes extinct, its role in the ecosystem is usually filled by new species, or other existing ones.

What is Mass Extinction?

·       Earth’s ‘normal’ extinction rate is often thought to be somewhere between 0.1 and 1 species per 10,000 species per 100 years.

·       This is known as the background rate of extinction.

·       A mass extinction event is when species vanish much faster than they are replaced.

·       This is usually defined as about 75% of the world’s species being lost in a ‘short’ amount of geological time – less than 2.8 million years.

About Late Ordovician mass extinction (LOME)

·       The Late Ordovician mass extinction (LOME) eliminated around 85% of the marine species from the earth.

·       It killed more than one-third of bryozoans and brachiopods.

·       It also destroyed several corals, conodonts, echinoderms, trilobites, bivalves and graptolites.

·       It did not affect the ecosystem of the structures as that of the other mass extinctions.

·       After the LOME, the lost biodiversity recovered during the first five million years of the Silurian period.

·       The LOME occurred in two distinct pulses. They are Katian and Hirnantian.

·       During the first pulse of LOME, called Katian, the earth shifted to ice cold climate from a green house climate. It led to continental glaciation. The continental glaciation was centred around Gondwana land which was then located in south pole. The falling sea levels and cooling destroyed the habitats. The fall in temperature killed several living organisms.

·       During the second pulse of LOME, called Hirnantian, the glaciers receded and warm conditions returned. Hirnantian was associated with Anoxia (meaning depletion of oxygen) and euxinia (meaning production of sulfides).

·       The LOME was followed by the Great Ordovician Biodiversification Event. This is the largest evolutionary surge in the biological history of the earth.

Causes of Late Ordovician mass extinction

·       The Late Ordovician mass extinction was caused by climate cooling, oxygen had no role in Late Ordovician mass extinction. The cooling climate likely changed the ocean circulation pattern. This caused a disruption in the flow of oxygen-rich water from the shallow seas to deeper oceans, leading to a mass extinction of marine creatures.

How many mass extinctions have there been?

Five great mass extinctions have changed the face of life on Earth.

1 - Ordovician-Silurian ME

·       It occurred 443 million years ago and wiped out approximately 85% of all species.

·       Scientists think it was caused by temperatures plummeting and huge glaciers forming, which caused sea levels to drop dramatically.

·       This was followed by a period of rapid warming. Many small marine creatures died out.

2 - Devonian ME

·       It took place 374 million years ago and killed about three-quarters of the world’s species, most of which were marine invertebrates that lived at the bottom of the sea.

·       This was a period of many environmental changes, including global warming and cooling, a rise and fall of sea levels and a reduction in oxygen and carbon dioxide in the atmosphere.

·       We don’t know exactly what triggered the extinction event.

3 - Permian ME

·       It happened 250 million years ago, was the largest and most devastating event of the five.

·       Also known as the Great Dying, it eradicated more than 95% of all species, including most of the vertebrates which had begun to evolve by this time.

·       Some scientists think Earth was hit by a large asteroid which filled the air with dust particles that blocked out the Sun and caused acid rain.

·       Others think there was a large volcanic explosion that increased carbon dioxide and made the oceans toxic.

4 - Triassic ME

·       It took place 200 million years ago, eliminating about 80% of Earth’s species, including many types of dinosaurs.

·       This was probably caused by colossal geological activity that increased carbon dioxide levels and global temperatures, as well as ocean acidification.

5 - Cretaceous ME

·       It occurred 65 million years ago, killing 78% of all species, including the remaining non-avian dinosaurs.

·       This was most likely caused by an asteroid hitting the Earth in what is now Mexico, potentially compounded by ongoing flood volcanism in what is now India.

The sixth mass extinction

·       The Holocene extinction, otherwise referred to as the sixth mass extinction or Anthropocene extinction, is an ongoing extinction event of species during the present Holocene epoch (with the more recent time sometimes called Anthropocene) as a result of human activity.

·       There have been several theories behind each mass extinction and with advances in new technologies, researchers have been uncovering more intricate details about these events.