2. EARTH’S EARLY ATMOSPHEREFORMED FROM OUT GASSING OFVOLCANOES.
3. Geologists have sequenced thegeologic events in past to develop ageologic history of Earth.Scientists use relative age andabsolute age to determine age offossils.
4. Relative age: the age of a fossil, rockor geological event in comparison toanother.
5. absolute age: the real age of afossil.
6. Index fossils: fossils used todetermine relative age of otherfossils, rocks and events.
7. a good Index fossil: wide-spread &lived short time period
8. Volcanic ash also is a good timemarker. Like index fossils wide-spread. Short time period.
9. Now complete page 102-113
11. Radioactive elements:• Radioactive element decay.• The amount of time it takes for half of aradioactive element to decay is half-life.• The half-life of an element cannot be changed.• The half-life of carbon 14 is 5,700 years.• The half-life of uranium 238 is 4.5 billionyears.
12. Carbon 14• Half-life 5,700• Used to date recent fossils-less than 50,000years.
13. Uranium 238• Halflife 4,500,000,000 years.• Uranium’s half life is how we know earth’sage.