1. Fossil Evidence
EQ: How do fossil records provide the history and changes of life on Earth?

2. Have you ever looked at a map of the world?
Did you notice how the coastlines of continents on opposite sides of the oceans appear to fit together like the pieces of a puzzle?

3. Is this a coincidence?
How is it that the coastlines fit together so well?
Is it possible that the continents were actually together sometime in the past?

4. Wegener’s Continental Drift Hypothesis
The hypothesis that the continents once formed a single landmass, broke up, and drifted to their present locations.

5. Pangea
Wegener made many observations before proposing his hypothesis of continental drift.
He thought that all the present continents were once joined in a single, huge continent called Pangea

6. Pangea “Pangaea” means “all earth”
It existed about 245 million years ago
It split into two huge continents about 180 million years ago
Laurasia
Gondwana
These two continents split again about 65 million years ago to form the continents we know today

7. Pangea Continental Drift explained a few puzzling questions
Why do the continents seem to fit together like a giant puzzle?
Why are fossils of the same plant and animal species found on continents that are on different sides of the Atlantic Ocean?
Why are rocks with different magnetic alignments found in the same place (paleomagnetism)?

8. Fossil Evidence
Fossils are the remains or physical evidence of an organism preserved by geological processes

9. Fossil Evidence How can we use fossils to learn about the past?
They give a rough sketch of the history of life on Earth
They show how the Earth’s environment has changed
They show how organisms have changed.
They help scientists date rocks.

10. Fossil Evidence
Scientists also noticed that fossils of the same species of extinct plants and animals are found in rocks of the same age, but on continents that are now widely separated.
Wegener believed that the organisms would not have been able to travel across the oceans.

11. Fossils can be found in…
Sedimentary rocks
Amber
Petrified wood/bone
Asphalt
Or they may be found preserved by ice!

12. Fossil Evidence
Usually when an organism dies, it is quickly consumed by other organisms.
But sometimes, the organism is quickly buried by sediment after they die.
These sediments slow down decay.
The hard parts of organisms, like shells and bones are more resistant to decay than soft tissues.
When the sediments lithify, the hard parts can become preserved
Fossils are usually found in sedimentary rocks

13. Relative Dating
One big puzzle for geologists to solve is the order in which events occurred during the past.
They rely on rocks and fossils to help them find out what life existed and the conditions of the Earth in the past.
Determining whether and object or event is older or younger than another object or event is called relative dating

14. Relative Dating
Sedimentary rock tends to be stacked in “layers”, like paper in a pile, with the oldest layers on the bottom and the youngest on the top
These layers are called strata

15. Relative Dating
This principle, that the youngest rocks lie above older rocks is called
The Law of SUPERPOSITION

16. But not all rocks are arranged with the youngest on top and the oldest on the bottom
Forces can disturb rocks
Rocks can be pushed into another sequence
Rocks can be tilted….
Folded….
and broken
Sometimes geologists find rock sequences upside down!

17. These disturbances make a scientist’s job very tricky!
To make their job easier, geologists combine information from known undisturbed rock sequences.
From this information, they create a geologic column, which is an ideal sequence of rock layers made of rocks and fossils arranged from oldest to youngest.

18. The columns are used to….
Interpret rock sequences
Identify the layers in puzzling rock sequences

19. Index Fossils
Scientists have found that particular types of fossils appear only in certain layers of rocks.
By dating the rock layers above and below these fossils, scientists can figure out the time span in which the fossilized organisms lived.

20. Index Fossils
If a type of organism lived for only a short period of time, its fossils would only show up in a few layers.
These types of fossils are called index fossils.

21. Index Fossils
Index fossils are fossils of organisms that lived during a relatively short, well-defined geologic time span
Examples include:
Ammonites
million years ago
Trilobites
400 million years ago