Our planet has existed for 4.5 billion years, and it has been a busy few eons. Here are the 25 biggest milestones in Earth's history. From leaps forward in evolution to devastating asteroid impacts, these were the turning points that shaped our world.
One thing stands out to me in all this: sex.
That is, once sex was invented, just over one billion years ago, the planet goes wild, as the kind of mutations and effects of natural selection, given reproduction by sex, increased exponentially, and filled the planet was quite easily filled with diverse life. It was only the first couple of steps it that boring first billion years that had to take so long to develop. Then sex was the key: that got us to where we are today, and is why evolution fits the timescale of our planet so well. Sex allowed amazing amounts of divergence in very short time spans. Without sex we wouldn't be here. Sex is the key.
A rough timeline:
4.6 billion years ago The origin of the Earth
3.8 billion years ago First life arises
2.1 billion years ago Eukaryotes evolved
1.1 billion years ago First sexually reproducing organisms
570 million years ago First arthropods evolve
530 million years ago The first fish
475 million years ago First land plants
385 million years ago First forests
370 million years ago The first amphibians
320 million years ago The earliest reptiles
225 million years ago The dinosaurs evolve
200 million years ago The mammals evolve
150 million years ago First birds
130 million years ago Flowering plants evolve
100 million years ago The first bees evolve
65 million years ago Dinosaurs and ammonites become extinct
14 million years ago The first great apes appear
2.5 million years ago Genus Homo evolves
0.2 million years ago Our species, Homo sapiens evolves
Until recently (less than a century ago) we didn't know how old the Earth was, nor how old the universe was, nor that the Earth was about 1/3rd as old as the universe. While so much is still mystery, what we know with an extreme level of confidence is mind-boggling.
First, it took almost a billion years (0.8 billion) for the Earth to cool down and stabilize for life to even start to form. Then what took the longest via natural selection was to get from the first living organisms to Eukaryotes, or organisms whose cells contain a nucleus and other structures enclosed within membranes. That was the most difficult step by far, and took over 1/3rd of the entire age of the Earth.
The other hurdle was getting from Eukaryotes having evolved to sexually reproducing species. It took another entire billion years just for sex to be invented. But that's also a very reasonable time frame. Those two steps together, developing Eukaryotes and then developing Sexual Reproduction, plus almost a billion years at first when the Earth was formed and couldn't support life yet, compromise the first 3.5 billion years of the Earth's existence, up to about just one billion years ago. And then the planet turns green. #scienceeveryday