Fossils tell about earth's history (teach)

Fossils tell us about Earth’s history

In the next few slides you will see fossils found either in or near Fort Worth.

Think about what these fossil remains of animals that lived 100 million years ago tell us about what Fort Worth was like long ago.

Fossils are the remains of things that once lived on Earth.

Gastropod casts

Oyster casts

Clam cast

Scallop cast

Sea urchin cast

Ammonite cast

Looking at these organisms, you can conclude they once lived:a. in a forest c. in a

grassland b. In an ocean d. in a desert

Yes, you could conclude that they once lived in an ocean.

So what must have been here in Fort Worth at that time (100 million years ago)?

Yes, at one time, very long ago, this area was covered by a shallow sea.

The North American continent during late Cretaceous time.

The Western Interior Sea covered most of the Midwest from the present Gulf of Mexico to the Arctic.

Sea fossils in Colorado

Area in Colorado where fossils are found

Sea fossils found in Utah

Area in Utah where fossils are found

Fossils of animals that lived in the sea can be found all throughout the western United States and Canada.

More evidence for what?

Colorado

TexasUtah

Western Interior Seaway during the mid-Cretaceous, about 100 million years ago.

Wikipedia Commons

Yes, more evidence for that ancient inland sea.

But then you might have noticed that the areas in Colorado and Utah where the fossils are found are now mountains. So somehow that flat seabed where the sea creatures of long ago lived is no longer flat—it is a chain of mountains.So something else must have happened.

Yes, after the inland sea, forces deep inside the Earth pushed up the flat seabed into huge mountains.

And right now, a new mountain range is being built in the middle of the Atlantic Ocean as magma flows from the mantle onto the ocean floor.Hundreds of millions of years in the future, a tall mountain chain will rise above the sea.

So over time, does the surface of the Earth stay the same?

The forces of nature constantly are changing the surface of the Earth creating new landforms and destroying others.

What does happen?

Usually these changes take a very, very long time-- tens of thousands, hundreds of millions of years. Once in a while they happen very quickly like an earthquake or landslide or some volcanic eruptions.