Geologic Time

Did you watch “Jurassic Park”? That word came from the Jurassic Period180 million years ago when dinosaurs ruled the earth. The Jurassic period was during the Mesozoic Era which started 240 million years ago! By contrast, the earliest ancestors of human beings first appeared on earth only 5-7 million years ago.

How do we know Earth’s History?

By studying Rocks and Fossils!

The history of earth is recorded in the rocks on the surface of earth, known as its Crust. Rocks have been formed, worn away, and re-formed right from the creation of the planet. These rocks undergo natural processes of Weathering and Erosion, typically due to wind and rain, to form Sediments. Sediments accumulate in layers known as Strata. Geologists dig up rock layers and study their composition to understand the nature of earth in the past.

Many rocks contain Fossils that reveal the history of life on earth. Fossils are preserved life forms of plants and animals. Imagine that an animal (maybe a dinosaur) fell and drowned in soft mud millions of years ago. The body of the animal would have rotted away but its bones would be preserved in the mud and protected by layers of sedimentary rock deposited on top. Even plants can be found preserved in this manner. Geologists dig up these fossils and study them to understand life on earth in the past.

Check Point

1. How old is earth estimated to be?
2. Dinosaurs ruled earth during the _______.
3. The last Ice Age was ______ years ago.
4. Earth’s history can be studied from ______ and ______.
5. Sediment accumulates in layers known as ______.

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