I. Early Life on Earth

• Earth formed about 4.6 billion years ago

• Earth was very hot

• Atmosphere - little Oxygen. Mostly water vapor, CO, CO2, and N2

• earth cooled the water vapor condensed, into bodies of water

• This became the home of the first cells (3.5 billion years ago)

II. Appearance of O2

• Bacterial cells produced the oxygen for the atmosphere

• Evolution of plants increased oxygen levels

III. Fossils

• Found mostly in sedimentary rocks

• Paleontologists use these to determine how an animal lived

• What we learn from studying fossils:– Where organisms lived

– How they moved

– What they could eat

– When organisms lived

– How organisms are related to each other

Types of Fossils

• Trace fossils- markings left by animals

• Petrified- minerals replace hard parts

• Casts- minerals in rock fill in spaces

Types of Fossils

• Amber- tree sap

• Imprints- organism falls into sediment

• Molds- buried in sediment and decays

IV. Dating Fossils

• Relative Dating– Based on where fossils

are in comparison to another

• Radiometric Dating– based on the amount of

an element found in a fossil

Radiometric Dating

• A pool of water began with 8 feet of water in it. If half of the water evaporates every day, and there is now 1 foot of water in the pool, how long has the pool been there?

• 8421

• 3 half lives x 1 day = 3 days

Radiometric Dating

• A block of wood is found to contain 5g of Carbon. If the block of wood began with 80g of carbon, and if half of the Carbon decays every 6,000 years, how long ago did the block of wood die?

• 804020105

• 4 half lives x 6000 years = 24,000 years ago

V. The Geologic Time Scale

• Life divided into four eras with different periods

• The Precambrian (3.5 BYA- 544 MYA) both a period and era

• Life forms very simple

• Precambrian 87% of Earth’s history

• Paleozoic Era (Old Animals)- (544-245 MYA)

• Many more types of plants and animals • First land plants and vertebrates• First mass extinction end of Paleozoic• 90% marine and 70% land species

disappeared

• Mesozoic Era(Middle Animals)- (245 MYA – 66 MYA)

• Mammals and dinosaurs appear during this time• Mammals were probably small to avoid dinosaurs

• The Jurassic Period of Mesozoic is “The Age of Dinosaurs”

• Another mass extinction wiped out dinosaurs and other species

• Continents moved during the Mesozoic (Plate Tectonics)

• Were all together in a landmass called Pangaea

• End of the Mesozoic, continents took their modern shape

• Cenozoic Era(New Life)- (66MYA – Present)

• Era we live in

• Larger mammals began to flourish

• Primates appeared

• Also when modern humans appeared– 200,000 Years Ago