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Above, modern human encroachment on Neanderthal-dominated territory. Hypotheses for the causes include conflict, competition and inter-breeding with modern humans, and failure to adapt to climate change. The answer is most likely a combination of any of these.

As of the 20th century, the accumulated harmful effects humans have been doling out to the environment begin taking a toll, and extinction rates skyrocket. Since 1900, mammals have been going extinct 28 to 55 times faster than they should. We have lost the Barbary Lion, and the Bali (in image), Javan and Caspian tigers among many others.

It is said we have officially begun experiencing the Sixth Mass Extinction.

Recent studies have shown that extinction rates are far above the natural rate, despite using very conservative estimates. As of the year 1500, mammals and birds are disappearing at 14 times the expected rate, and reptiles, amphibians and fishes at 5 times the rate. Notable extinctions include aurochs, the ancestors to cattle, and Steller’s sea Cow (in image).

About three-quarters of plant and animal life died during the Cretaceous-Tertiary mass extinction. Aside from a few turtle and crocodile species, no tetrapods weighing over 25 kilos survived. Evidence points to an impact caused by a large (10-15km wide) comet or asteroid which devastated the biosphere through a prolonged impact winter, halting photosynthesis.

Triassic-jurassic Extinction saw a whole class of marine life (Conodonts) disappear, along with up to 34% of marine genera. On land, the scenario is poorly understood, but there was a large turnover in amphibian and land-dwelling reptiles, giving way to the dinosaur and crocodile families that many are familiar with today.

The Permian-triassic Extinction was the third and most severe one recorded. Up to 96% of marine species, around 76% of terrestrial vertebrates species and 83% of insect genera disappeared. The reasons behind this are unclear, with possibilities ranging from meteoric impact to simple sea rise.

 

As Pangaea begins to form, the land is populated with plants and insects, and the oceans harbor massive coral reefs full of stromatoporoids (sea sponges). The Late Devonian Extinction spanned up to 25 million years and affected marine life, wiping out 50% of genera. (image: Stromatoporoid fossil).

The Ordovician-Silurian Extinction affected nearly all taxonomic groups present at the time, wiping out nearly 85% of marine species.

We are experiencing a Climate Crisis. CO2 levels are rising by 2.1ppm per year, and human population is growing by 1.1% per year, (Human population at 7.5 billion, CO2 at 410ppm). 15 of the 24 ecosystems on Earth are endangered and global warming is nearing critical tipping points.

 

The Great Acceleration begins. Between 1900 and 1950, our implementation of the internal combustion engine and coal-powered electricity in our everyday lives leads to rapid population and economical growth. Human population doubles from 1 to 2 billion in 50 years.

 

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