Our planet has been around for four and a half billion years, going back and forth for generations. Next, I'll take you through some of the major milestones in earth's history.
4.5 billion years ago, the earth was born
The earth grows in a cloud of dust and rock around the sun. The earth was formed by a collision with thousands of rocks. Eventually it had enough mass to attract other rocks with gravity, and eventually became the earth.
4 billion to 3.5 billion years ago
No one knows exactly how long ago life really began, but the oldest fossils have been confirmed to be single-celled microbes, 3.5 billion years ago. Life may be a little bit older than 3.5 billion years ago, but it can't have been there by collisions, because life may have started in the sea bed, but we don't know what the earliest creatures looked like.
2.4 billion years ago, the great oxidation event
For the first half of earth's history, there was no oxygen in the air. But then some bacteria began to use sunlight to make sugar from carbon dioxide and water, just as plants do today. These organisms excrete oxygen as a metabolite, giving us the oxygen-rich atmosphere we have today.
1.2 billion years ago, the origin of reproduction
First, the first reproduction occurred between 1.8 billion and 800 million years ago. But it is not clear why the creatures did not simply split into two, but instead began physical reproduction, and it is still very messy. Why this date is certain is that there are fossils of red algae that apparently formed specialized germ cells at that time.
450 million years ago, plants colonized the land
As early as 450 million years ago, there were actually animals venturing onto land, but just for the sake of looking, probably to lay eggs.
370 million years ago, fish walked on land
As plants have moved to land and taken root, the next step is to leave the ocean. Something called a "titalic" slowly emerged and landed. Eventually limbs evolved and gave rise to amphibians, reptiles and mammals. Before long, however, the late devonian mass extinction wiped out many Marine animals.
160 million years ago, the first bird
Birds evolved from feathered dinosaurs. The most famous early bird, archaeopteryx, lived about 150 million years ago.
65 million years ago, the dinosaurs went extinct
Sixty-five million years ago, a huge rock from outer space struck what is now Mexico. The explosion was devastating, and the dust entered the upper atmosphere, blocking out the sun, followed by darkness and cold. There were five such devastating impacts that wiped out the earth's dinosaurs, but pterosaurs and giant sea creatures also disappeared.
The first hominid between 13 and 7 million years ago
The first ape man appeared in Africa 25 million years ago. And then at some point, ape-man split into the ancestor of modern humans and the ancestor of ape-man. It's hard to say exactly when, but thanks to a lot of fossils that have been found in modern times, we know that the earliest hominids were "chudshahs," who lived about 7 million years ago.
200,000 years ago, humans
Our species, homo sapiens, has less than a tenth of the earth's existence. Here we expand from the birthplace of Africa to every corner. Our existence experienced the sixth mass extinction and altered climate change in earth's history. But we've never figured out which species we are.
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