origins of life on earth
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Origins of Life on Earth. Oldest Fossils. Evidence shows Earth is 4.6 billion years old. Earth cooled and solidified 4.2 billion years ago. The oldest fossils indicating life are 3.5 billion years old. - PowerPoint PPT PresentationTRANSCRIPT
Origins of Life on Earth
• Evidence shows Earth is 4.6 billion years old. Earth cooled and solidified 4.2 billion years
ago. The oldest fossils indicating life are 3.5 billion
years old. These are stromatolites, rocks created by
prokaryotes binding layers of sediment together
Oldest Fossils
Dating Fossils1.radiometric dating - measures the decay of a
radioactive element in the fossil2.other methods - # of tree rings, amino acid
racemization
Radiometric Dating14C - decay of C14 to N14 over time.half-life of 5730 yearsevery 5730 years, 1/2 of the remaining amount is
converted to 14N.
235U - measures decay of Uranium-235 to Lead-207 (207Pb)
half-life (t1/2) for U-235 is 713 million years.
A sample of bone is found to contain 25% of its original 14C. How old is it?
Originally 100%-->50%-->25% t1/2 t1/2Thus, 2 half-lives x 5730 = 11460 years old
Primary Abiogenesis 1st life arose from non-living materialsformed spontaneously from 1st organic molecules (containing carbon) in 1950’s Miller-Urey’s experiment reproducing early Earth conditions resulted in formation of simple organic molecules100 Greatest Discoveries: Orig
in of Life : Video : Science Channel
How Did Life Begin?
• a four-stage process proposed:1.Small organic molecules, like amino acids,
form from simple molecules2.the simple organic molecules join together
into larger ones, like proteins and nucleic acids
3.Molecules could copy themselves and provide the basis for reproduction and inheritance.
4.These molecules are enveloped in membranes to form the first pre-cells.
Where Did Life Begin?3 hypothesis:
1. Ocean Surface shallow tidal pools or moist clay harsh atmosphere makes this
difficult
2. Deep Sea Vents heated inorganic molecules mixing
with water can find archaebacteria still living in
these vents
3. Panspermialife didn’t begin on earth but arrived on
meteors and comets from space‘seeded’ life on earthMurchison Meteorite crashed into Australia in
1969scientists found it contained amino acids,
including some not found on earthalso contained sugars
Eukarya DevelopmentEndosymbiosis prokaryotic cell membrane ‘folded in’ resulting
in organelles ancestral prokaryotes developed symbiotic
relationships with each other insideeventually formed eukaryotic cellsmitochondria and chloroplasts have own DNA
Sexual Reproduction & Meiosisallowed for more genetic diversityonce variation in alleles, natural selection
could occurchange could occur rapidly, resulting in
multicellular organismsex adaptive radiation
Geologic Time Scale & Erasdivide Earth’s history into blocks called erasend of each era marked with period of major
changePrecambrian: 4.6 billion – 542 mya
Paleozoic Era542 – 251 mya
Mesozoic Era261 – 65.5 mya
Cenozoic Era65.5 mya – modern day
Mass Extinctionsmost eras ended as a result of mass extinctionleft a niche for new organisms to evolve to fill
those nichesadaptive radiation5-6 major mass extinctions in Earth’s history