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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.