Mader: Biology 8th Ed.
Origin and History of Life
Chapter 19
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Mader: Biology 8th Ed.
Outline
• Primitive Earth• Origin of First Cells• Fossils• The Precambrian• The Paleozoic• The Mesozoic• The Cenozoic• Continental Drift• Mass Extinctions
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Mader: Biology 8th Ed.
The Primitive Earth
• 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
• 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
• 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
• Protocells would have been precursors to the first true cells.
– A protocell is a structure with a lipid-protein 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
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Fossils
• 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
• 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
• 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
• 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
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The Precambrian
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
– Permian
!Excess carbon dioxide.
!Loss of 90% of ocean species.
– Triassic
!Meteorite Collision
– Cretaceous
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Review
• Primitive Earth• Origin of First Cells• Fossils• The Precambrian• The Paleozoic• The Mesozoic• The Cenozoic• Continental Drift• Mass Extinctions
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