The History of Life The record and origin of life.

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.