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. • These are stromatolites, rocks created by prokaryotes binding layers of sediment together
Dating Fossils 1.radiometric dating - measures the decay of a radioactive element in the fossil 2.other methods - # of tree rings, amino acid racemization
Radiometric Dating 14C - decay of C14 to N14 over time. • half-life of 5730 years • every 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 t1/2 • Thus, 2 half-lives x 5730 = 11460 years old
How Did Life Begin? Primary Abiogenesis • 1st life arose from non-living materials • formed spontaneously from 1st organic molecules (containing carbon) • in 1950’s Miller-Urey’s experiment reproducing early Earth conditions resulted in formation of simple organic molecules • 100 Greatest Discoveries: Origin of Life : Video : Science Channel
a four-stage process proposed: • Small organic molecules, like amino acids, form from simple molecules • the simple organic molecules join together into larger ones, like proteins and nucleic acids • Molecules could copy themselves and provide the basis for reproduction and inheritance. • These molecules are enveloped in membranes to form the first pre-cells.
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 Where Did Life Begin?
3. Panspermia • life didn’t begin on earth but arrived on meteors and comets from space • ‘seeded’ life on earth • Murchison Meteorite crashed into Australia in 1969 • scientists found it contained amino acids, including some not found on earth • also contained sugars
Eukarya Development Endosymbiosis • prokaryotic cell membrane ‘folded in’ resulting in organelles • ancestral prokaryotes developed symbiotic relationships with each other inside • eventually formed eukaryotic cells • mitochondria and chloroplasts have own DNA
Sexual Reproduction & Meiosis • allowed for more genetic diversity • once variation in alleles, natural selection could occur • change could occur rapidly, resulting in multicellular organisms • ex adaptive radiation
Geologic Time Scale & Eras • divide Earth’s history into blocks called eras • end of each era marked with period of major change Precambrian: 4.6 billion – 542 mya
Paleozoic Era • 542 – 251 mya
Mesozoic Era • 261 – 65.5 mya
Cenozoic Era • 65.5 mya – modern day
Mass Extinctions • most eras ended as a result of mass extinction • left a niche for new organisms to evolve to fill those niches • adaptive radiation • 5-6 major mass extinctions in Earth’s history