Dinosaurs were alive longer than they’ve been extinct.

Mesozoic dinosaurs

Dinosaurs have been extinct for 65 million years. That’s a long time, but not nearly as long as they were alive for: 165 million years. Their reign as the planet’s dominant species absolutely dwarfs our own, which began a few hundred thousand years ago, and accounts for just 0.007% of the Earth’s history — a blink of the cosmic eye. If you compressed the planet’s history into one calendar year, dinosaurs would have appeared on January 1 before going extinct in the third week of September; humans, meanwhile, wouldn’t have shown up until December 31.

Dinosaurs lived in the Mesozoic Era, which began 252 million years ago and was divided into three periods: Triassic, Jurassic, and Cretaceous. Many of the most well-known species had already gone extinct by the time others appeared; for instance, more time separated Stegosaurus and Tyrannosaurus (80 million years) than separated the T. rex and humans. It wasn’t until 1677 that the first fossil was discovered, not that the man who came upon it had any way of knowing what it was — he thought the bone in question belonged to a giant.

By the Numbers

Did you know?

Not all paleontologists think an asteroid killed the dinosaurs.

Though what’s known as the Alvarez hypothesis is the most widely accepted theory for what caused the dinosaurs to go extinct, not all paleontologists think an asteroid was responsible. Others believe the dinos met their doom gradually rather than suddenly, with increased volcanic activity at the end of the Cretaceous spewing so much dust and soot into the atmosphere that the sun was eventually blocked out. Those who belong to the latter camp are referred to as “intrinsic gradualists” rather than “extrinsic catastrophists,” as they contend that the K-T boundary separating the age of dinosaurs from the age of mammals was of an earthly nature, and occurred over the course of millions of years.