1. 12.1 The Fossil Record KEY CONCEPT Specific environmental conditions are necessary in order for fossils to form.

2. 12.1 The Fossil Record Fossils can form in several ways. Permineralization occurs when minerals carried by water are deposited around a hard structure.

3. 12.1 The Fossil Record A natural cast forms when flowing water removes all of the original tissue, leaving an impression.

4. 12.1 The Fossil Record Trace fossils record the activity of an organism.

5. 12.1 The Fossil Record Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.

6. 12.1 The Fossil Record Preserved remains form when an entire organism becomes encased in material such as ice.

7. 12.1 The Fossil Record Specific conditions are needed for fossilization. Only a tiny percentage of living things became fossils.

8. 12.1 The Fossil Record Radiometric dating provides an accurate way to estimate the age of fossils. Relative dating estimates the time during which an organism lived. –It compares the placement of fossils in layers of rock. –Scientists infer the order in which species existed.

9. 12.1 The Fossil Record Radiometric dating uses decay of unstable isotopes. –Isotopes are atoms of an element that differ in their number of neutrons. neutrons protrons

10. 12.1 The Fossil Record –A half-life is the amount of time it takes for half of the isotope to decay. Radiometric dating uses decay of unstable isotopes. –Isotopes are atoms of an element that differ in their number of neutrons.

11. 12.1 The Fossil Record KEY CONCEPT 12.3 The origin of life on Earth remains a puzzle.

12. 12.1 The Fossil Record Earth was very different billions of years ago. There have been many hypotheses of Earth’s origins. The most widely accepted hypothesis of Earth’s origins is the nebula hypothesis.

13. 12.1 The Fossil Record Several sets of hypotheses propose how life began on Earth. There are two organic molecule hypotheses. –Miller-Urey experiment –meteorite hypothesis electrodes heat source amino acids water “atmosphere” “ocean”

14. 12.1 The Fossil Record There are different hypotheses of early cell structure. –iron-sulfide bubbles hypothesis

15. 12.1 The Fossil Record There are different hypotheses of early cell structure. –lipid membrane hypothesis

16. 12.1 The Fossil Record A hypothesis proposes that RNA was the first genetic material. –Ribozymes are RNA molecules that catalyze their own replication. –DNA needs enzymes to replicate itself.