Transcript A View of Life

Origin and History of Life
Chapter 19
Mader: Biology 8th Ed.
Outline
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Primitive Earth
Origin of First Cells
Fossils
The Precambrian
The Paleozoic
The Mesozoic
The Cenozoic
Continental Drift
Mass Extinctions
Mader: Biology 8th Ed.
The Primitive Earth
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Primitive atmosphere most likely consisted
of water vapor, nitrogen, and carbon dioxide,
with small amounts of hydrogen and carbon
monoxide.
– Little free oxygen.
– Originally too hot for anything but water
vapor to form.
– Earth cooled and water vapor condensed
to liquid water.
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Monomers Evolve
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Stanley Miller (1953) conducted an
experiment to show the first organic
molecules could have been produced from
primitive atmospheric gases in the presence
of strong energy sources.
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Polymers Evolve
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Monomers join to form polymers in the
presence of enzymes.
– Protein-First Hypothesis assumes DNA
genes came after protein enzymes arose.
– RNA-First Hypothesis suggests only RNA
was needed to progress toward formation
of the first cell or cells.
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Protocell Evolves
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Protocells would have been precursors to
the first true cells.
– A protocell is a structure with a lipidprotein membrane that carries on energy
metabolism.
 Semipermeable-type boundary may
form around coacervate droplets.
 Liposomes form in liquid
environments.
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Protocell Anatomy
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Origin of First Cells
Mader: Biology 8th Ed.
Fossils
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Fossils are remains and traces of past life.
– Great majority are found embedded in, or
recently eroded from, sedimentary rock.
 Sediment becomes a stratum.
 Recognizable layer in stratigraphic
sequence.
 Paleontology is the study of the
fossil record.
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Fossils
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Relative Dating of Fossils
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Strata change their character over great
distances.
– A stratum of the same age tends to
contain the same fossil.
 Helps geologists determine relative
dates of the strata despite upheavals.
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Strata
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Absolute Dating of Fossils
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One absolute dating method relies on
radioactive dating techniques.
– All radioactive isotopes have a particular
half-life.
 Length of time it takes for half of the
radioactive isotope to change into
another stable element.
 Compare radioactivity of a fossil to
that of a modern sample of organic
matter.
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The Precambrian
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Comprises about 87% of the geological
timescale.
– First cells came into existence.
 Prokaryotes
 Cyanobacteria in ancient
stromatolites added oxygen to the
atmosphere.
 Lack of ozone shield allowed UV
radiation to bombard Earth.
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Prokaryote Fossil of Precambrian
Mader: Biology 8th Ed.
The Precambrian
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Eukaryotic Cells Arise
– Eukaryotic cell arose about 2 bya.
 Nearly always aerobic and contains
nucleus as well as other membranous
organelles.
 Endosymbiotic Hypothesis.
Multicellularity Arises
– Multicellularity arose approximately 1
billion years later (1.4 bya).
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The Paleozoic
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The Paleozoic era lasted over 300 million
years.
– Contained three major mass extinctions.
 Disappearance of a large number of
species, or a higher taxonomic group,
within a relatively small time interval.
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Cambrian Animals
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Molecular Clock is based on principle that
DNA differences in certain parts of the
genome occur at fixed rate, and are not tied
to natural selection.
– Number of base-pair differences tells how
long two species have been evolving
separately.
 High Cambrian diversity may be due to
the evolution of outer skeletons.
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Cambrian Sea Life
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Invasion of Land
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Plants
– Seedless vascular plants date back to
Silurian period and later flourished in
Carboniferous period.
Invertebrates
– Outer skeleton and jointed appendages of
arthropods are adaptive to living on land.
Vertebrates
– Evolution of fishes began in Ordovician.
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The Mesozoic Era
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Evolution of many plants and animals
continued into the Triassic, the first period of
the Mesozoic era.
– Nonflowering seed plants became
dominant.
– Dinosaurs achieved enormous size.
– Mammals remained small and
insignificant.
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The Cenozoic Era
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Mammals began an adaptive radiation at the
end of the Mesozoic era, moving into habitats
left vacant by the demise of dinosaurs.
– Flowering plants already diverse and
plentiful.
– Primate evolution began.
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Factors That Influence Evolution
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Continental Drift
– Positions of continents and oceans are
not fixed.
 Modern mammalian biological diversity
is the result of isolated evolution on
separate continents.
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Continental Drift
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Continental Drift
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Plate Tectonics
– Movements of Earth’s crust which is
fragmented into slablike plates that float
on a lower hot mantle layer.
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Plate Tectonics
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Mass Extinctions
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At least five mass extinctions have occurred
throughout history. At the ends of:
– Ordovician
 Continental Drift
– Devonian
 Bolide Event
 Loss of 70% of marine invertebrates
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Mass Extinctions
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Permian
 Excess carbon dioxide.
 Loss of 90% of ocean species.
Triassic
 Meteorite Collision
Cretaceous
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Review
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Primitive Earth
Origin of First Cells
Fossils
The Precambrian
The Paleozoic
The Mesozoic
The Cenozoic
Continental Drift
Mass Extinctions
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.