1. EARTH SCIENCE

2. A TRIP THROUGH GEOLOGIC TIME
FOSSILS

3. How a Fossil Forms BrainPOP
Fossils-the preserved remains or traces of living things
Fossil formation
Living thing dies and is buried in sediment
Sediments slowly harden into rock and preserve the shapes of the organism

4. Cast- a solid copy of the shape of an organism
Mold Fossil ---
Mold- a hollow area in sediment in the shape of an organism or part of one
Cast- a solid copy of the shape of an organism
Cast Fossil ---

5. Petrified Fossils- fossils in which minerals replace all or part of an organism
Carbon Films- an extremely thin coating of carbon on a rock
Trace Fossils- provide evidence of the activities of ancient organisms

6. Change Over Time
Paleontologist- a scientist who studies fossils
They use the fossil record to build a picture of Earth’s past environment
The fossil record shows that older rocks contain simpler organisms while younger rocks contain more complex ones
This supports the theory of evolution
Scientific theory- a well tested concept that explains a wide variety of observations
Evolution- the gradual change in living thihngs over time

7. Quick Check 1. What is a fossil?
2. In general, how does a fossil form?
3. What are the five different kinds of fossils?
4. What does the fossil record show about how life has changes over time?
5. What type of scientists studies fossils?

8. The Relative Age of Rocks

9. Relative vs. Absolute Age
Relative age
Absolute age
Age compared to other rocks
The number of years since a rock has formed

10. The Position of Rock Layers
The law of superposition- In horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the one below it.

11. Determining Relative Age
Geologists use clues from igneous rock and faults
Clues from igneous rock:
Igneous rock is formed from hardened magma
Magma that hardens on the surface is called extrusion; this rock is always younger than the rock below it
Magma that cools below the surface is called intrusion; this rock is always younger than the rock that surrounds it

12. Clues from faults:
A fault is a break in Earth’s crust
A fault is always younger than the rock it cuts through
To determine the relative age of the fault, geologists determine the age of the lowest layer cut by the fault

13. Index Fossils
An index fossil is one that is widely distributed and that represents an organism that existed only briefly
Index fossils ell the relative ages of the rock layers in which they occur

14. Quick Check
1. In your own words, explain the difference between relative age and absolute age
2. What is the law of superposition?
3. What are the three types of clues that geologists use to find the relative age of rocks?

15. Radioactive Dating

16. Radioactive Decay BrainPOP
All rocks are made of matter, all matter is composed of atoms
Most elements are stable, but others are not
Overtime these unstable elements break down during a process called radioactive decay
During this process atoms of one element break down into atoms of another element

17. Half life All unstable(radioactive) elements have a “half life’
Half-life- the amount it takes for half of the radioactive element to decay

18. Radioactive Elements Elements commonly used in radio active dating:
Carbon-14
Potassium-40
Rubidium-87
Thorium-232
Uranium-235

19. Quick Check 1. Define “radioactive decay
2. How does the composition of a radioactive element change over time?
3. If the half life of Carbon-14 is 20 years, how much carbon-14 will be left in a 100g sample after 100 years have passed? Show your work

20. The Geologic Time Scale

22. Geologic time scale- a record of the life forms and geologic events in Earth’s history
Divisions of the Geologic Time Scale:
Eras
Eras are divided into periods

23. Early Earth

25. 1. Planet formation
Rocks, ice and debris collided to become our planet. It was hot, fiery and hit by asteroids.

28. 2. Atmosphere formation
Earth was hot with volcanoes and magma. Eruptions released toxic gasses that became a protective layer (atmosphere)

29. Volcanoes and gasses

30. 3. Rain and Land formation
Volcanoes released water, which cooled and condensed in the atmosphere to make clouds. The clouds rained, and rain cooled the surface of the magma.

33. 4. Ocean formation
In the low areas, water accumulated. These become oceans.

34. Oceans

35. 5. Life & Oxygen formation
The first form of life developed in the oceans. These were one-cellular, plant-like bacteria that used photosynthesis to get energy.

36. Blue-Green Algae
(Cyanobacteria)

37. Stromatolites

39. How do we know?
A geyser in Nevada spews boiling water six feet. Cyanobacteria-ancient oxygen-producing algae-leave blue-green streaks on the rock, a moist, mineral-rich environment that may resemble the setting where the first life evolved.