This document discusses fossils found in and near Fort Worth, Texas that provide evidence about the area's history. The fossils are of marine animals like gastropods, oysters, clams, and scallops that lived 100 million years ago. This indicates that the Fort Worth area was once covered by a shallow sea. At that time, a large inland sea also covered much of the central United States. Similarly, marine fossils found in Colorado and Utah show that region was also underwater in the past. The land has since been uplifted, showing the surface of the Earth is constantly changing over millions of years through geological forces.

1. Fossils tell us about
Earth’s history

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

3. Gastropod casts

4. Oyster casts

5. Clam cast

6. Scallop cast

7. Sea urchin cast

8. Ammonite cast

9. 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.

10. 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.

11. Sea fossils in
Colorado

12. Area in Colorado where fossils are found

13. Sea fossils found in Utah

14. Area in Utah where fossils are found

15. Fossils of animals that lived in the sea can be
found all throughout the western United
States and Canada.
Colorado
Utah
Texas
More evidence
for what?

16. Yes, more
evidence for
that ancient
inland sea.
Wikipedia Commons
Western Interior Seaway during the mid-
Cretaceous, about 100 million years ago.

17. 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.

18. 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.

19. So over time, does the surface of the
Earth stay the same?
What does happen?
The forces of nature constantly are
changing the surface of the Earth creating
new landforms and destroying others.
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.