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

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

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)(1/2 n ) ; n= ½ lifes

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

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

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, CO 2 and H 2 O

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

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

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)