What Was It Like When Mammals Evolved And Rose To Prominence?
“65 million years ago, 99.5% of the Universe’s history had already unfolded, and yet the ancestors of modern humans were no better developed than a modern-day lemur. Complex, differentiated animals had already existed for half-a-billion years, but it seems to be mere chance that led to the rise of an intelligent, technologically-advanced species like us. We do not yet know what secrets other planets hold as far as life goes, but here on Earth, the most remarkable story of all was just getting truly interesting.”
It was some 550-600 million years ago that life’s complexity exploded, at least in the fossil record, at the start of the Cambrian period. While that epoch marks
the first complex, differentiated, macroscopic, multicellular, sexually-reproducing animals arising and dominating the oceans, life would go on to develop traits that were absolutely necessary for eventually giving rise to human beings. Animals developed spinal cords, four limbs, moved onto land, became warm-blooded, and more. Most importantly, many such creatures were able to survive enormous extinction events, enabling them to rise to prominence when a previously-occupied niche opened up.
It took half a billion years from the Cambrian explosion for mammals to rise to prominence, but after the big K-T extinction event, we were the most adaptable organism left. Here’s the story of how mammals like us evolved and came to dominate the Earth.
Are Mass Extinctions Periodic, And Are We Due For One?
“If we start looking at the craters we find on Earth and the geological composition of the sedimentary rock, however, the idea falls apart completely. Of all the impacts that occur on Earth, less than one quarter of them come from objects originating from the Oort cloud. Even worse, of the boundaries between geological timescales (Triassic/Jurassic, Jurassic/Cretaceous, or the Cretaceous/Paleogene boundary), and the geological records that correspond to extinction events, only the event from 65 million years ago shows the characteristic ash-and-dust layer that we associate with a major impact.”
65 million years ago, a catastrophic impact from outer space caused the last great mass extinction on Earth, destroying 30% of the species that lived on our world at the time. These mass extinction events happened many times in Earth’s past, and the Solar System also passes through denser stellar regions of space periodically, as determined by the orbit of the Sun and stars in the Milky Way. It’s a combination of facts that might make you wonder whether the extinction events are also periodic, and if so, whether periodic impacts are predictable. If so, then shouldn’t we be aware of whether we’re living in a time of increased risk, and prepare ourselves for that possibility accordingly? After all, the dinosaurs didn’t have a space program or the capability of deflecting a dangerous object like the one that wiped them out.
But before we go that route, we should take a good look at what the data shows. Are mass extinctions periodic? Are we due? Let’s find out!