The world looked a bit differently 66 million years ago.  Pangaea had splintered into Africa, Antarctica, Australia, Eurasia, North America and South America.  Antarctica was connected to Australia, and Eurasia to North America.  Moreover, South Asia formed an island between Africa and Eurasia.  This was also a warm world without any ice sheets.  The deserts seem to have been smaller too.  Combined this means there were proportionally more vegetation.  The oxygen content of the air was almost one and ha half times as high as it is today.  Giant insects were still impossible for purely ecological reasons.  Pterosaurs and birds had taken over their niche.

At the very end of the Cretaceous volcanism greatly increased.  Although biological diversity was in the decline the consequences would not have been so large without an additional catastrophe.  An asteroid measuring 10 kilometres (6¼ mile) hit the Gulf of Mexico.  The heat from this impact melted rock and made the sea around it evaporate away.  In a broad zone around this nearly everything died from the heat.  Molten rock rained down over parts of North and South America.  The tsunami from the explosion drowned islands up to the size of Madagascar.  All this only consisted the immediate consequences.  They were over in a few days.

The more long term consequences were even more devastating globally.  The impact immediately combusted oil found in the bedrock there.  It also created a wave of heat which then put plants on fire all over the world.  Most of the world’s vegetation burned up in the resulting fires.  Microscopic pieces of molten rock solidified into dust in the air.  In addition there was pulverized rock ejected but not melted.  All this smoke and dust blocked a great deal of sunlight.  In a few months the temperature sank by 10°C (6°F).  Above all, it was the darkness and cold which lead to species going extinct.

It took several years for the atmosphere to recover from this impact.  Before that too little could grow to sustain a viable population of any large animals at all.  Same applied to phytoplankton and algae in the seas.  Large animals which had not died in the beginning starved or froze to death.  Where the temperature was above freezing fungi temporarily took over.  Decomposing plant material and mushrooms became food for certain small animals.  Then I mean segmented worms, arthropods and small molluscs.  They in turn become food for some smaller animals.

Some plants survived in the form of seeds and spores.  Sweetwater environments did not suffer that hard since they usually did not freeze.  There many amphibians, small crocodilians and turtles survived.  Nothing warm-blooded over 10 kilograms (22 pound) survived.  Birds which survived either resembled waterfowl or mainly lived on the ground.  The latter could eat seeds, insects, snails and worms.  Same applies to mammals surviving this mass extinction.  Most were additionally capable of digging dens in ground.  Like wetlands and watercourses these protected against the wave of heat and fire.

Maybe the most interesting is how the ancestors of humanity survived.  The best candidate I know about was the North American Purgatorius.  As a tree dwelling seed and insect eater it most closely resembled a tree shrew.  It was not a digger but could make use of larger animals’ dens.  From this or something comparable the monkeys later evolved and by extension us.

Uploaded on the 2nd of September 2024.