EARTH’S HISTORY
Mass Extinction Events on Earth
What will cause the next one? Humans or Aliens?
Posted originally on July 9, 2020 by Nimisha Singla for Teach for Green
Waiting for an apocalypse? Well, getting wiped out from the face of the earth does sound like quite an adventure…
Would you believe me if I told you that our earth has gone through periods of such massive changes that they wiped out nearly 60% (and more) of all of the world’s species every time? And this has happened not twice or thrice, but five times?
Unbelievable? Well, not really. Given our Earth’s age, a whopping 4.6 billion years, one can imagine that there have to be changes which the planet has undergone. Besides, all of us are familiar with the fate of the dinosaurs. However, that right there is the reason why this is exciting and worthy of being studied. Most of us know just about the dinosaurs.
A big part of understanding who we are (who are we?) and what our purpose on the planet is (why do we exist?) is deeply rooted in the study of evolution and genetics. While those are very interesting questions that are sadly out of the scope of this blog, the author will try to inculcate a sense of wonder and appreciation for all living beings who co-habitat Earth with us.
Every time we lose a species to extinction (due to human or natural causes), it is almost like losing a toy that you haven’t even played with yet. While that is an extremely utilitarian approach, it’s a good way to even begin imagining the loss.
For the purpose of this blog, we will go over the five periods of mass extinction briefly and try to answer whether we are on the verge of the sixth mass extinction. These five mass extinctions are the Ordovician Mass Extinction, Devonian Mass Extinction, Permian Mass Extinction, Triassic-Jurassic Mass Extinction, and Cretaceous-Tertiary (or the K-T) Mass Extinction.
Their cause and effect were way scarier than their names, so without further ado, let us get right into it.
1. The Ordovician Mass Extinction (440 million years ago)
Life was just in its beginning stages on Earth when it experienced the first known mass extinction. Nearly 85% of all living species went extinct! This is attributed to shifts in continental plates and a “snowball” event, in which the entire surface of the earth is covered by ice (“ice age”). Rapid melting of all the ice followed. Both times the climate changed so swiftly that the organisms could not adapt to it.
2. The Devonian Mass Extinction (375 million years ago)
Much of a mystery, this extinction removed 80% of living species from the face of the planet. As plants claimed land, they removed much of the carbon dioxide from the atmosphere which changed the composition of air. Some believe massive volcanic eruptions and meteor strikes have had a role to play too.
3. The Permian Mass Extinction (250 million years)
The largest of all known mass extinctions, 96% of all species were wiped out. Research claims that it was a series of events that led to this event. Volcanic eruptions suffocated the atmosphere by cutting off the oxygen supply and blocking out sunlight — prerequisites to most life on Earth — the most likely starting point of a chain of reactions.
4. The Triassic-Jurassic Mass Extinction (200 million years ago)
More than half of all living species were eliminated in this series of smaller extinctions throughout the Triassic and Jurassic geological ages. The sea levels changed and so did the chemistry of our oceans. Climate changes led to drastic transitions which were hard to cope with.
5. The Cretaceous-Tertiary (K-T) Mass Extinction (65 million years ago)
Along with the dinosaurs, this latest extinction event took away 75% of life. An asteroid hit Earth, sending debris into the air and resulting in an “impact winter”. This however is sometimes treated only as a trigger and there might be other underlying causes. Nevertheless, sudden changes in temperatures again proved fatal yet again.
Armed now with a better understanding of what all factors can impact life on Earth, what do you think — are humans witnessing another mass extinction as it unfolds? Passenger Pigeons, West African Black Rhinoceros, Tasmanian Tigers — are all species that are no longer with us. There are many more in line. Are humans in the queue too?
It seems we are at the mercy of heavenly bodies and other fellow human beings.
References:
https://onekindplanet.org/top-10/top-10-worlds-extinct-animals/
