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)(1/2n) ; 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, CO2 and H2O

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)