Transcript The History of Life

THE HISTORY
OF LIFE
Ch 14
EARTH’S EARLY HISTORY
Evolution is a scientific THEORY based
on different types of evidence collected
over the years
Evidence Includes:
 Earth was an inhospitable planet
Hot
 Volcanic gasses
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First organisms appeared between 3.5
to 3.9 billion years ago
There is direct evidence of Earth’s
history
 Fossils & rocks show that Earth
formed about 3.9 billion years ago
HISTORY IN ROCKS
Fossils = any evidence of an organism
that lived long ago
 Trace fossils – something left by an
animal (example footprint, trail, burrow)
 Casts – minerals in rocks fill a space left
by a decayed organism (form a replica of
organism)
 Petrified fossils – minerals replace the
hard parts of an organism
 Imprints – thin objects can leave an
imprint as sediments turn to rocks
 Amber-preserved & frozen – actual
organism is trapped in amber or ice
Dunkleosteus (30 ft long; bony skull shown
here is about 1 meter high)
Extinct at the end of the Devonian
FOSSIL EXAMPLES
STUDYING FOSSILS

Paleontologists study fossils
Kinds of organisms that lived
 Learn about behavior
 Earth’s climate
 Geography (rivers, continent position)
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Fossils are found in sedimentary rock
Organism is buried in mud, sand, or clay soon after
death
 Particles compress & harden over time to form
sedimentary rock
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DETERMINING FOSSIL AGE
Relative dating
 Surface layers are newest so they have the most recent
fossils.
 Deeper layers contain older fossils
 Scientists can determine the order of appearance &
extinction
Radiometric dating
 Uses radioactive isotopes
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Potassium 40 (half life of 1.3 billion yrs)
Carbon 14 (half life of 5730 years)
Scientists can approximate ages
THE GEOLOGIC TIME SCALE

A time scale of Earth’s existence based
on fossil evidence
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4.6 billion years ago – present
Divided into Eras
Precambrian, Paleozoic, Mesozoic, Cenozoic
 Distinguished by organisms that lived
during the era
 Eras are divided into periods

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Mass extinction = entire groups of
organisms disappear from the fossil
record almost all at once
PRECAMBRIAN ERA

87% of Earth’s history
3.5 billion years ago to 544 million years ago
 Began with prokaryotes
 Eukaryotes developed and flourished
 Soft-bodied invertebrates (jellyfish, sponges)
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Oldest fossils – 3.5 billion years old
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resemble forms of modern species of cyanobacteria
Stromatolites – evidence of photosynthetic bacteria
PALEOZOIC ERA

Beginning (Cambrian period)
Dramatic increase in diversity of life forms
 Worms, sea stars, trilobites in the oceans
 Fish appeared – oldest animals with backbones
 Land species – ferns & seed plants
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Middle – amphibians
 End – Reptiles
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Largest mass extinction – 90% of Earth’s marine
species & 70% of the land species disappeared
MESOZOIC ERA
Began about 245 million yrs ago
 Triassic
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Jurassic (began ~ 280 million years ago)
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Mammals appeared on Earth
Early mammals were small and mouselike
Age of the Dinosaurs
Birds appeared
Evidence of bird relation to dinosaurs
Cretaceous (began ~ 144 million years ago)

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New types of mammals & flowering
plants
Mass extinction of dinosaurs ~ 66 million
years ago
GEOLOGICAL EVENTS OF THE MESOZOIC
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Geologic evidence of a large crater East of Mexico
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Continental Drift
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Could have filled the atmosphere with dust, changing
climate
Pangaea broke apart & continents began to move
apart
Plate tectonics = Earth’s crust consists of several
rigid plates on top of molten rock.
Plates continuously move
 Explains continental drift
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CENOZOIC ERA

Began ~ 66 million years ago – the current era
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Mammals began to flourish
Primates appeared (~30 million years ago)
 Modern humans appeared (~200,000 yrs ago)
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14.2 ORIGIN OF LIFE
THE ORIGIN OF LIFE ON EARTH

Abiogenesis – life from non-living things and
Spontaneous Generation = idea that nonliving
material can produce life
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Primordial Soup – natural processes formed early
organic compounds
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Disproven by Redi and Pasteur
Miller-Urey experiment
Biogenesis = living organisms only come from
other living organisms
REDI
&
PASTEUR
THE ORIGIN OF CELLS
Prokaryotes – Archaebacteria (1st cells)
 Eukaryotes – endosymbiont hypothesis

Separate DNA in chloroplasts and mitochondria
 Both organelles the same size and shape of bacteria
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