History of Life Ch and 17.2

Paleontology The study of fossils ▫Structures of organisms ▫Diet ▫Predators ▫Habitat ▫Related species and common ancestors

The Fossil Record Incomplete due to conditions necessary to form fossils Usually found in sedimentary rock Includes imprints and fossilized organic material

Relative Dating Principle of Superposition - fossils in lower layers are older than fossils in upper layers – Shows change over time – Shows extinctions 99% of all species that have ever existed are now extinct! Index fossil – easily recognized species that existed for a short period of time over a wide geographic range can allow for estimate of other fossils’ age

Radioactive Dating Radioactive decay – elements break down over time into different elements ▫Half-life – length of time for half of the radioactive atoms in a sample to decay  Amount of time differs by element  Used to calculate age of fossils/rocks

Geologic Time Scale Represents evolutionary time Based off of fossils, rock layers, radioactive dating Divided into eras and periods

Earth’s History Approx. 4.6 billion years old Nebular hypothesis – “space dust” condensed due to gravity into sun and planets Cooling allowed solid rocks (4 bya) and liquid water (3.8 bya  formation of oceans) Early atmosphere: poisonous! ▫Hydrogen cyanide, CO 2, CO, N 2, H 2, Sulfide, H 2 O

Miller-Urey Hypothesis 1950’s - Americans Miller and Urey tested how organic molecules may have formed ▫Sterile flask w/ hydrogen, methane, ammonia and water was exposed to electric sparks ▫Amino acids were formed from the inorganic compounds! ▫Repeated experiments reduced error and showed production of N. bases

Miller-Urey Experiment

Origin of Life Approx my after formation of liquid water, cells were common Microfossils of prokaryotes dated to 3.5 bya Proteinoid microspheres – organic molecules form bubbles with selectively permeable membranes and ability to store/release energy RNA led to the evolution of DNA

Change in Earth’s Atmosphere Evolution of photosynthetic bacteria common during Precambrian Time ▫O 2 combined with iron in oceans and oceans became blue-green! ▫O 2 accumulated in ozone layer to turn skies blue! Caused many organisms to go extinct and allowed for evolution of new species

Evolution of Eukaryotes Endosymbiotic Theory - prokaryotes began living inside of other prokaryotes ▫DNA and ribosomal evidence in mitochondria and chloroplasts ▫Organelles divide by binary fission

Evolution of Eukaryotes, cont. Sexual reproduction allowed for faster rate of evolution due to increased variability Multicellular organisms allowed cell differentiation