Sea plants and first multicellular organisms emerge. 11:00 PM: Dinosaurs arrive. 11:40 PM: Dinosaurs go extinct. 11:58 PM: Modern humans (Homo sapiens) appear.

While the planet itself is billions of years old, most of the complex life and recorded history we study occurred in the final few "minutes" of its existence.

Scientists arrived at this number primarily through of meteorite fragments and the oldest known rocks from the Earth and Moon. By measuring the decay of radioactive isotopes (like uranium turning into lead), geologists can calculate how much time has passed since the rock formed. The timeline in perspective

To make that massive number easier to visualize, imagine Earth’s entire history squeezed into a single : 12:00 AM: Earth forms. 4:00 AM: First simple, single-celled life appears.