“In the last half-billion years, life on Earth has been nearly wiped out five times — by such things as climate change, an intense ice age, volcanoes, and that space rock that smashed into the Gulf of Mexico 65 million years ago, obliterating the dinosaurs and a bunch of other species. These events are known as the Big Five mass extinctions, and all signs suggest we are now on the precipice of a sixth.” Nadia Drake, National Geographic.
The thought of this planet staring into the abyss of its sixth mass extinction event scares the life out of me, but the fear has also pushed me to want to understand this topic in more detail. I am no specialist on this topic but having thought about this during the last holiday weekend I wanted to explore the history of earth’s mass extinction events that almost wiped out all living life on this planet. I thought it would be a good idea to put this thinking down on paper and use it to write my next blog post.
The big five extinction events
The first mass extinction event took place around 439 million years ago with 86% of life wiped out. It was called The Ordovician-Silurian mass extinction and scientists believe that this was the result of glaciation and falling ice levels as well as vast quantities of plant life covering the earth, removing too much carbon dioxide from the air which drastically lowered the temperature.
Next up was The Devonian mass extinction event. This took place around 370 million years ago with 70–80% of life wiped out. I couldn’t find evidence of a single cause, it seems to be a collection of stresses on the planet’s biodiversity such as global warming (or cooling) and/or meteorite impacts.
The largest of the extinction events The Permian-Triassic mass extinction — also known as the “great dying” — took place around 250 million years ago with approximately 90% of life being wiped out. Like the Devonian extinction event it is hard to identify a single cause but it is believed that the event was caused by acid rain following an enormous release of volcanic gases.
The Triassic-Jurassic mass extinction event took place around 200 million years ago and killed off 76% of marine and terrestrial species on Earth. A number of scientists agree that over a short period of time, volcanic eruptions spewed large amounts of lava and gas. This release of gases could have created catastrophic global warming and acidification of the oceans. The Cretaceous-Paleogene mass extinction event took place around 66 million years ago with 75% of life wiped out — some species such as leatherback sea turtles and crocodiles survived. The cause of this event was a number of large asteroid impacts.
Fast forward to today and planet earth is staring at the next mass extinction planet earth has encountered. This event is known as the Holocene extinction. The name comes from Holocene Epoch, a period of time, approximately 11,700 years that started after the last ice age. The continuous extinction of species that is coinciding with the Holocene Epoch is a consequence of human activity. This led me to think about how big of a role do we actually play as co-living inhabitants of this planet?
In terms of size, humans are very small inhabitants of planet earth
Industrial revolution’s as well as other global events and innovations has meant the role humans play on this planet has always been a dominant one. This is despite having a very small biomass (total weight of organisms on earth). To elaborate, the earth’s biomass is measured in Gigatons (GT) ~ 1 gigaton equals 1,000,000,000 metric tons. Animal biomass stands at 2 GT with humans (7.6 billion) accounting for 0.06 GT — only 0.01% of the earth’s total biomass! This is less than Arthropods, which accounts for 1 GT.
Of the rest of the earth’s biomass distribution Carbon accounts for 4 GT; Archaea 7 GT; Fungi 12 GT; Bacteria 70 GT; Plants 450 GT.
“Humanity is a biological species, living in a biological environment, because like all species, we are exquisitely adapted in everything: from our behavior, to our genetics, to our physiology, to that particular environment in which we live. The earth is our home. Unless we preserve the rest of life, as a sacred duty, we will be endangering ourselves by destroying the home in which we evolved, and on which we completely depend.” Edward O. Wilson
My conclusion
If 0.01% of the earth’s biomass has the ability to trigger a mass extinction event, then it also has the ability to prevent it. This bluey green dot, suspended in the universe, is home to 8.7 million other forms of life — we must do all that we can to protect it.
I was fascinated to learn that the enormous amounts of plant life covering the earth could have contributed to the first mass extinction event on earth. What I took from this was the need for balance and equilibrium and that too much of one thing will never be a good thing.
Sources:
Worldatlas.com; Britannica.com; Nationalgeographic.com; Thoughtco.com; MIT.edu; Vox.com
