the fossil record paleontology is the study of the fossil record to document life’s early history...
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The Fossil Record• Paleontology is the study of the
fossil record to document life’s early history– Documents patterns within species
living at a specific time and area– Documents extinctions and new
arrivals– Documents evolution of life as the
environment of Earth changed• Index (Key) Fossils are those
found in similar strata over a wide area… used for relative dating
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Formation of Fossils• Whole remains…
– Requires a soft substrate (sand, snow, riverbed, tar pit,…)
– Organism must be buried and protected for the elements
• Fossils can be evidence of life– Footprints, tunnels and burrows
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Absolute Dating of Fossils
• Uses the presence of a radioactive isotope and the principle of half-life to determine the age of the organism– Sometimes called radioactive or radio dating– Half-live… the amount of time it takes for ½ of a substance to
undergo radioactive decay• C-14 has a half life of 5730yrs, so… if you had 100g of C-14 there
would be 50g left in 5730yrs, 25g left in 11460yrs, 12.5g in 17190yrs – (mass)(1/2n) ; n= ½ lifes
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Geologic Time Scale • eon - longest division – Archeon - 1st eon of Earth ~3.9 to 2.5 billion
years ago – Proterozoic - lasted for the next 2 billion
years – Phanerozoic - most resent with evidence of
life • era - there are three eras per eon
– Paleozoic - ~543 million years ago "Age of Invertebrates" • fossils of both land and plants
– Mesozoic - ~248 million years ago "Age of Reptiles" • dinosaurs
– Cenozoic - ~most recent "Age of Mammals" • appearance of humans
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Geologic time scale• periods
– Precambrian - all periods before the paleozoic era • rocks lack index fossils • fossil evidence is contained in stromatolites - layers of bacteria and algae • Oldest are anaerobes ~3.5mil yrs. ago
– Cambrian • invertebrates • trilobites is the most common index fossil ~500 million years ago
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Early Earth• Early (protoplanet) Earth is struck
by a large object (Mars size) (~4.6Billion yrs ago)– Provides the energy for the geologic
process necessary for the rearrangement of Earth’s materials
– The atmosphere lacks oxygen (anaerobic) and contains toxic gases, CO2 and H2O
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First Organic Molecules
• ~ 3.8 Billion years ago the Earth cools enough for water to remain a liquid– C compounds from space and inorganic
compounds from the atmosphere form the beginnings of RNA… “primordial ooze”• Replicated in a lab by Miller and Urey in
the 1950s to produce Urea
– Eventually form proteinoids or microspheres
– RNA develops the ability to self replicate
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Oxygen Revolution– Oxygen toxic to anaerobes creates mass extinctions
• Seen in layers of stromatolites
– photosynthesis and the oxygen revolution (cyanobacteria) ~2.2billion years ago• prokaryotes start using oxygen as a source of reducing energy to form new
molecules • photoautotrophs … enters in the age of Eukaryotes
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Age of Eukaryotes• Eukaryotes (~2.1 billion years ago) – arose from the symbiotic relationship and transfer of
genetic material between prokaryotes • organisms resemble simple single celled algae
– Endosymbionts - mitochondria & plastids • endosymbionts take over the role of energy making paving the
path for multicellular organisms – genetic annealing (combining of genomes) and colony formation leads
to specialization and the multicellular organism
• multicellular organisms (~1.5 billion years ago) – most confined to areas of water and heat (snowball Earth hypothesis)
resembling small algae – Cambrian explosion (explosion of life ~ 700mil years ago)