The History of LifeThe History of Life

The record The record

and and

origin of lifeorigin of life

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: Paleontologists: scientists, scientists, “detectives” of the “detectives” of the pastpast

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

frozenfrozen– MoldsMoldsPage 378Page 378

How are fossils formed?Page 381

• 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 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 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 time Periods are time

frames within frames within eraseras

• 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

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

Mesozoic, cont.Mesozoic, cont.Continental Drift

1. Pangaea = one large continent

2. 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

**plate tectonics

CenozoicCenozoic

• 66 million yrs ago

• Mammals thrive

• Primates appear (30 million yrs ago)

• Humans – 200,000 years ago

Early thoughts on origin of life…

Redi Pasteur

Spontaneous generationSpontaneous generation: idea that nonliving material can produce life.

Two experiments that helped disprove this notion:

Biogenesis: life comes from life!

Modern thoughts on origin of life…

Primordial soup

Protoce

ll

Formatio

n

NOW: Hydrothermal vents

Evolution of Cells•The first true cells

•Prokaryotes that evolved from protocells

•Anaerobic; heterotrophs

•Similar to Archaebacteria

•Photosynthesizing prokaryotes

•Aerobic

•The endosymbiont theory

•Eukaryotes evolved from a symbiotic relationship with prokaryotes.