Hello, my name is Jimmy the grasshopper and I will tell you about the geological eras.

Hi Jimmy, I am Tad. I can't wait to learn about the geological eras!

They are different periods in Earth's history. You can think of it as cutting a pizza into four slices, where the slices represent the Precambrian era, the Paleozoic era, the Mesozoic era, and the Cenozoic era.

So what is a geological era?

The Precambrian was the period before the Cambrian Explosion, which was the really the explosion of life! It began about 4.6 billion years ago and lasted about 4 billion years, which is more than 85% of Earth's history.

Wow! Those are some big numbers!

During this era, there was very simple life in the oceans. In fact, the organisms were so small that you could barely see them.

Was life even smaller than my antennae?

Yes, most of it was.

So what era came after the Precambrian?

It's called the Paleozoic era. It lasted 345 million years. At this time, primitive plants had started to grow and creatures walked on land for the first time.

There was a lot of oxygen in the air at this time, so the creatures were bigger. There were prehistoric dragonflies that had the wingspan of an eagle and spiders that were the size of wolves.

Ahhh! Look behind you!

Woah, what happened? Everything looks so dry and lifeless.

The Paleozoic era ended with a mass extinction. Over 80% of all life on earth vanished. It was a troubling time for our ancestors.

So when did the dinosaurs come in?

The dinosaurs lived during the Mesozoic era, which came after the Paleozoic.

Dinosaurs dominated the Earth for over 150 million years. They were big and small, ate meat and plants, and were one of the most successful species. Also, there is a theory that birds are descended from dinosaurs.

Tell me about the dinosaurs.

It's a asteroid. But it wasn't just big; to wipe out the dinosaurs, it had to be enormous!

What's that big thing in the sky?!

So that's it? All of a sudden the dinosaurs were just... gone?

No, it didn't happen quite that fast.

When the meteorite hit the Earth, it blew large amounts of debris into the atmosphere. Soon after, the debris formed a cloud around the planet, preventing sunlight from reaching the Earth. This is what killed the dinosaurs and most other life.

What era came next?

The Cenozoic era followed this mass extinction. Up until now, reptiles had dominated the earth, but this time, life took a different course. Mammals, the creatures that had been lying low, began to develop and evolve. In time, they would populate the globe.

And then came the ice age. In fact, there have been many other ice ages in Earth's history, but this was the most recent one.

It's... so... cold. I think my antennae are frozen

But eventually, after about 2.5 million years, the glaciers started to retreat. By then, many of the ancient creatures, such as mammoths and saber-toothed tigers, no longer existed.

Finally, it's starting to feel warmer around here. That's too bad about the mammoths though.

When did humans first appear?

Modern humans appeared about 200 thousand years ago, but their primate ancestors evolved long before that, between 25 and 30 million years ago.

So what era is this?

We are living in the Cenozoic era still.