The Earth has been around for a while — about one-third as long as the universe itself. By comparison, Homo sapiens are the new kids on the block. Earth’s story began at the outset of the Hadean eon, about 4.6 billion years ago. It took 600 million years just for the Earth’s crust to take shape, another 300 million years for the first signs of microbial life to pop up, and about 3.2 billion years after that for life to really get going thanks to the evolutionary burst known as the Cambrian explosion. Several mass extinction events and some 465 million years later, mammals finally took center stage, but modern humans didn’t enter the biological limelight for another 65 million years. With the first Homo sapiens appearing around 300,000 years ago, humans have only been on planet Earth for 0.0067% of its existence.
In those 300,000 years, humans have been pretty busy. For a couple thousand years, we harnessed fire and lived a nomadic existence, until around the fourth millennium BCE, when the very first civilizations began to take shape. Since then, humans have been on a meteoric trajectory, going from hunter-gatherer to spacefarer in less than 6,000 years. Carl Sagan famously displayed the universe’s history on a 365-day calendar, with the Big Bang on January 1 and our current moment starting at 12:01 a.m. the next year. On that timeline, it’s only at 10:30 p.m. on December 31 that humans first appear, and all of recorded history is squeezed into just a few seconds — but what a few seconds it’s been.
Geologists divide the life of the Earth into various categories of time. First, there are eons, which stretch for millions and sometimes billions of years. Then come eras, followed by periods, epochs, and finally ages. For the past 11,700 years, since the end of the Paleolithic ice age, the rise of humanity has coincided with the Holocene Epoch (which is part of the Quaternary period of the Cenozoic era). For most of this epoch, the world’s climate remained stable, but with the rise of modern society, the Earth has undergone rapid changes in a very short time. That’s why many scientists believe that a new epoch, called the Anthropocene (meaning “recent age of humans”), should be adopted, beginning around 1950 and the dawn of the nuclear age. For the Anthropocene to become official, both the International Commission on Stratigraphy and then the International Union of Geological Sciences need to sign off. Despite support within these groups, the epoch has yet to be officially recognized.