EARTH’S EARLY ATMOSPHEREFORMED FROM OUT GASSING OFVOLCANOES.
Geologists have sequenced thegeologic events in past to develop ageologic history of Earth.Scientists use relative age andabsolute age to determine age offossils.
Relative age: the age of a fossil, rockor geological event in comparison toanother.
absolute age: the real age of afossil.
Index fossils: fossils used todetermine relative age of otherfossils, rocks and events.
a good Index fossil: wide-spread &lived short time period
Volcanic ash also is a good timemarker. Like index fossils wide-spread. Short time period.
Now complete page 102-113
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.
Carbon 14• Half-life 5,700• Used to date recent fossils-less than 50,000years.
Uranium 238• Halflife 4,500,000,000 years.• Uranium’s half life is how we know earth’sage.