History of the EarthHistory of the Earth

History of the Earth

• Earth is believed to be about 5 billion5 billion years old

• Little available atmospheric oxygen at this time

• First life on earth is believed to have been 3.9ish billion3.9ish billion years ago – in oceans

What’s the evidence for this?

• Paleontologists: scientists, Paleontologists: scientists, “detectives” of the past“detectives” of the past

• FOSSILS!FOSSILS!– TraceTrace– CastsCasts– PetrifiedPetrified– ImprintsImprints– Amber-preserved/frozenAmber-preserved/frozen– MoldsMolds

How Are Fossils Formed?

• Most dead organisms don’t fossilize because of bacterial and fungal activity

1. Organism falls into river

2. Rushing water covers the dead body with sediment; minerals move into the body

3. Time passes and more sediment compresses; minerals replace bone

4. Earth movements reveal fossil millions of years later

Where Are Fossils Found?

• Sedimentary rock forms layers compressing older dead, decaying organisms.

Fossil Dating

Relative DatingRelative Dating

• Determined by layers of rock above fossil

• Geological LAW• Depicts order of

appearance and/or extinction of organisms

• Age is only in relation of other fossils

Radiometric DatingRadiometric Dating

• Helps determine SPECIFIC age

• Amount of radioactive isotope decay (half-life)

• Potassium-40 = half-life of 1.3 billion yrs

• Carbon-14 = half-life 5730 years

• Often inconsistent

Geologic Time Scale

• 4 basic Eras4 basic Eras• Periods are Periods are

time frames time frames within eraswithin eras

• Major life forms Major life forms dictate periodsdictate periods

PrecambrianPrecambrian

• 3.5 billion yrs ago

• 87% of earth’s history

• Major life: only prokaryotes at first then 1.8 billion yrs ago, eukaryotes appeared

Stromatolites: mats formed by cyanobacteria.

PaleozoicPaleozoic• 245 million years

ago• Cambrian period

brought biodiversity

• Fish then amphibians then reptiles (oh my!)

• Mass extinction knocked out 90% of marine and 70% of land biodiversity

Plate-skinned fish

MesozoicMesozoic

• 245 million yrs ago• Jurassic period = “the

age of the dinosaur”• Fossil evidence shows

that modern birds evolved from dinosaurs

• New kinds of mammals and flowering plants

• Cretaceous Period ended with another mass extinction 66 million yrs ago (meteorite collision!)

Yanoconodon: fossil shows evidence of evolution from reptilian jaws and ears to

mammalian

MesozoicMesozoic

Continental Drift1. Pangaea = one

large continent2. 135 million years

ago two large land masses: Laurasia & Gondwana

3. 66 million years ago – most of the continents had broken apart

**this affects organism distribution

CenozoicCenozoic

• 66 million yrs ago

• Mammals thrive• Primates appear

(30 million yrs ago)

• Humans – 200,000 years ago