1. Evolution and Fossils

2. Fossils:
Fossil: the preserved or mineralized remain or imprint of an organism that lived long ago.

3. Age of rocks can tell us the age of fossils

4. Fossils are remains of ancient life

5. 3 major points on evolution through the use of the fossil record:
EVIDENCE:
3 major points on evolution through the use of the fossil record:
Earth is about 4.5 billion years old
Organisms have inhabited Earth for most of its history
All organisms living today evolved from earlier, simpler life forms

6. Plants can also become fossils
Most fossils form when organisms and traces of organism are rapidly buried in fine sediments deposited by water, wind or volcanic eruptions
Paleontologists: scientists who studies fossils.

7. Becoming A Fossil
Scientists have described about 250,000 different fossil species
Yet that is a small fraction of those that lived in the past!
Evolution can be seen in the fossil record.
Fossilized species found in older rocks are different from those found in newer rocks

8. Fossil formation
The oldest fossils are remains of marine organisms that populated the planet's oceans.
When they died, the plants and animals were buried by mud, sand, or silt on the sea floor.
Land animals and plants usually decomposed or were eaten, and mainly the hard parts -- teeth, bones, shells, or wood -- were preserved.

9. Fossils can be formed in several ways
Buried bone and shell contain tiny air spaces into which water can seep, depositing minerals.
Reinforced by these mineral deposits, bone and shell can survive for millions of years.
Even if the bone or shell dissolves, the mineral deposits in the shape of the body structure remain.

10. Quick Recap:
Arrange fossils in sequence from oldest to youngest to see patterns of evolution
Fossils are classified according to the way they are found

11. Fossils are found in layers of rock

12. Remember:
The oldest rock layers (and therefore the oldest fossils) are always on the bottom
The youngest are on top.
This is referred to as superposition (super = above)

13. Oldest to the bottom:

14. Picture time:

15. Becoming a Fossil

16. Organisms die and are buried by sediment

17. Layers Accumulate
Their weight causes the lower layers to harden into sedimentary rock, trapping the organism or trace inside.

18. Not all fossils are formed by sediment
Found in Amber
Found in Tar Pit

19. Becoming a Fossil
Casts: a mold of an organism is created and then filled by minerals making an exact copy
Molds: AN organism decays leaving an empty space in the rock that is the exact shape of the organism
Imprints: Thin objects such as leaves or feathers fall into mud and then mud hardens
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20. Types of Fossils:
Trace Fossils: Evidence of animal activity (footprints, trails, etc.)
Petrified fossils: the hard part of the organism is replaced with minerals and the minerals harden making an exact stone copy.
Amber-preserved: Rare, but when found whole organism is preserved.

21. Interpretation of fossils poses another set of challenges
Their age can only be estimated by radiometric dating of rocks they were found near or within

22. Dating Fossils: Relative dating: Radiometeric dating:
fossils on the bottom are the oldest, and the ones on the top are the youngest
Only tells if one fossil is older than another
Radiometeric dating:
radioactive isotopes are used to determine age of fossil

23. Fossils can show us how ecosystems change
Nevada’s Silver Peak Mountain Range

24. Fossil of a marine animal found in the rocks of the desert

25. Archaeocyathids were a group of sponges that lived about 500 million years ago, and are now extinct.
They built huge reefs (similar to coral reefs we see today) and were extremely important members of their ecosystems

26. What could explain finding fossils of sponges in the Nevada desert?