An extinction refers to the death of all members of a species. A mass extinction is an event when most of the species on Earth die in a relatively short period of time.

Life on Earth began at the bottom of the oceans almost four billion years ago. Over time, it evolved from a tiny single-celled bacteria into myriads of different forms and sizes – eventually rising onto the land and further up to the skies. Multiple times, life has also been wiped out for all but a small proportion of living organisms, yet always paving the way for new species. Perhaps the best-known of these mass extinction events¹ was caused by an enormous asteroid (if not a comet or meteoroid) that brought to an end the era of dinosaurs (the Cretaceous-Paleogene mass extinction).

Dinosaurs began to evolve some 240 million years ago (after the Permian mass extinction). They remained small and relatively insignificant creatures for tens of millions of years, living in the shadows of other peculiar beings before growing unimaginable sizes and shapes (after the Triassic mass extinction). Some became the largest land animals ever to walk on our planet (Argentinosaurus), others beasts never seen before or after (Tyrannosaurus rex), ready to take over the world.

The reign of dinosaurs lasted long but came to an end suddenly once an asteroid, ten kilometres wide, crashed into Chicxulub, modern-day Mexico, about 66 million years ago. The devastating hit left behind 160 kilometres wide and 40 kilometres deep crater (now filled with soil and mostly hidden beneath the sea). It likely killed all creatures instantaneously within a thousand kilometres, followed by tsunamis, wildfires, and acid rain, continuing to demolish life on land and in the water.

The full impact, however, must have taken thousands of years. A dust cloud was thrown to the skies, blocking the sun and cooling the planet into a nuclear winter. In the cold and dark, it is estimated that almost three-quarters of the plant and animal species living on Earth became extinct, including all dinosaurs (except birds).

Thousands of years after the blow, life began to recover once again. New species came into being, and over time, one of those species evolved into a deceptively harmless-looking frail ape – an animal that was to cause the next mass extinction.

¹ There have been five known mass extinctions in the past. Ordovician-Silurian 444 MYA, Devonian 374 MYA, Permian (or the Great Dying) 252 MYA, Triassic 200 MYA, and Cretaceous-Paleogene 66 MYA. These mass extinctions have been caused, whether alone or together, by massive volcanic eruptions, asteroids or meteoroids crashing into Earth, and sudden changes in our planet's climate, so rapid that animals had no time to adapt to new environments. Besides, we are currently facing a sixth mass extinction. Unlike the previous catastrophes that threatened life on Earth, the current mass extinction is caused by an animal. A human.

Bibliography

Brusatte, S. 2019. The Rise and Fall of the Dinosaurs. London, United Kingdom: Picador. 404 p. ISBN 9781509830091. Pages 15-18, 34, 43, 81, 85-87, 96-99, 112, 146, 197-201, 315-318.

Brusatte, S. 2022. The Rise and Reign of the Mammals. London, United Kingdom: Picador. 500 p. ISBN 9781529034233. Pages 165-168.

Panciroli, E. 2022. The Earth a Biography of Life The Story of Life On Our Planet Through 47 Incredible Organisms. London, United Kingdom: An Hachette UK company. 255 p. ISBN 9781529413984. Pages 47, 73, 109, 127, 131, 142-143, 167, 180-183, 240.

Frankopan, P. 2023. The Earth Transformed an Untold History. London, United Kingdom: Bloomsbury Publishing. 695 p. ISBN 9781526622563. Pages 25-32.

Rutherford, A. 2014. Creation The Origin of Life. London, United Kingdom: Penguin Books. 272 p. ISBN 9781780229072. Page 60.

Dartnell, L. 2019. Origins How the Earth Shaped Human History. London, United Kingdom: Penguin Random House. 346 p. ISBN 9781784705435. Pages 141-143.

Natural History Museum (2023). What is mass extinction and are we facing a sixth one? Available at: https://www.nhm.ac.uk/discover/what-is-mass-extinction-and-are-we-facing-a-sixth-one.html (Accessed: 8 August 2023).

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