Deep time and the age of dinosaurs
The Mesozoic on a clock
Teaching this? Open projector mode
Geologists divide time into eras and periods. Dinosaurs lived in the Mesozoic Era, which lasted from about 252 to 66 million years ago (written Ma, “mega-annum”), roughly 186 million years in all. It has three periods:
- Triassic: about 252 to 201 Ma
- Jurassic: about 201 to 145 Ma
- Cretaceous: about 145 to 66 Ma
The first dinosaurs, such as Eoraptor and Herrerasaurus from Argentina, were small and appeared about 230 Ma in the Triassic. The non-bird dinosaurs died out at the end of the Cretaceous, about 66 Ma.
Dinosaurs were not all alive together. Stegosaurus lived in the Late Jurassic, about 150 Ma. Triceratops and Tyrannosaurus rex lived at the very end of the Cretaceous, about 68 to 66 Ma, in the same part of western North America.
So the gap from Stegosaurus to T. rex is more than 80 million years. And T. rex lived only about 66 million years before today. That means T. rex is closer in time to us than to Stegosaurus.
Millions of years are hard to picture. Squeeze the whole 4.54 billion years of Earth’s history into one 24-hour day and the Mesozoic looks like this:
- First dinosaurs (230 Ma): about 22:47, roughly 73 minutes before midnight
- Stegosaurus (150 Ma): about 23:12
- Non-bird dinosaurs die out (66 Ma): about 23:39, 21 minutes before midnight
- Homo sapiens (about 300,000 years ago): the last 6 seconds
Dinosaurs were around for roughly 50 minutes of that day. Humans are a brief last moment.
Which lived earlier, Stegosaurus or Tyrannosaurus rex?
In which era did the dinosaurs live?
Which statement is true?
On the 24-hour clock of Earth’s history, about when did the non-bird dinosaurs die out?