Transcript Chapter 25 - Brown Biology

Chapter 25
The History of Life on Earth
The History of Life on Earth
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Macroevolution- the pattern of evolution
over large time scales.
Earliest evidence of life: 3.5 byo fossils
How did the first living cells appear?
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Abiotic synthesis of small organic molecules
Joining of these molecules into macromolecules
Packaging of these molecules into protobionts
Origin of self-replicating molecules that made
inheritance possible
Synthesis of Early Earth
Formed about 4.6 billion years ago
 Oparin and Haldane- primordial soup
 Miller and Urey- tested Oparin and
Haldane hypothesis in lab- produced
multiple amino acids and other organic
compounds
 Protobionts- collections of abiotically
produced molecules surrounded by a
membrane-like structure
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Fossil Record
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Absolute Dating
◦ Radiometric Dating- based on the decay of
radioactive isotopes
◦ Half-Life- the time required for 50% of the
parent isotope to decay.
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Challenges
◦ Organisms do not use radioisotopes that have
long half-lives.
◦ Sedimentary rocks have compounds of
different ages.
The Geologic Record
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Geologic Record- divided into three eons
◦ Archaean
◦ Proterozoic
Together lasted approx. 4 billion years
◦ Phanerozoic- the last half billion years- divided
into three eras
 Paleozoic
 Mesozoic
 Cenozoic
First Organisms
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Stromatolites- layered rocks that form when
certain prokaryotes bind thin films of
sediment together.
Endosymbiosis- mitochondria and plastids
took residence inside a prokaryote to form
a eukaryote
◦ Evidence
 Mitochondria and chloroplasts have own DNA
 Ribosomes
 Mitochondria and chloroplasts replicate independently
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Cambrian Explosion- many phyla of living
animals appear suddenly in fossils formed
early in the Cambrian period (535-525
mya)
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Continental Drift- the movement of
Earth’s plates, over time.
◦ Supercontinent- formed three times
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Mass Extinction- large number of species
become extinct throughout Earth.
◦ Consequences: disrupt a thriving ecological
community, disappearance of evolutionary
lineage
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Evolution is like tinkering- a process in
which new forms arise by the slight
modification of existing forms. Even large
changes, like the ones that produced the
first mammals, can result from the gradual
modification of existing structures or the
slight modification of existing
developmental genes.
◦ Francois Jacob (modified)