Geologic Time and Life in the Oceans Oceans and Life Oceans are the birthplace of life. Life metabolism, growth, reproduction, response to stimuli Metabolism use of energy stored in ambient chemicals Reproduction production of viable offspring with similar to identical charactisteristics How Old is Earth? The Solar System? Archbishop Usher of Armagh, Ireland (1581-1656) Earth created at 9:00 AM on October 26, 4004 BC Eastern Standard Time or Rocky Mountain Time? 1800 s - physicists and geologists realize Earth must be very old Halley (1715) - Salinity of oceans increased with time Joly (1899) calculated an age of 90 million years Lord Kelvin estimated the age of Earth 24 to 40 million years old, based on how fast it cooled down, but he was wrong. 1
Relative Dating Older, younger Correlation Geologic Time Absolute Dating Measuring years before present Years after a specific event Relative Dating Fossils are generally contained in sedimentary deposits With time, new fossils are deposited on top of old fossils A Relative Dating B C D E In what order did these features form? 2
Relative Dating Correlation Relating common sediment strata over great distances Fossils, lithology, Stratigraphy Absolute Dating Radioactive Elements provide a natural clock Most elements are stable, but some are not. Formed during differentiation of the planet and perhaps from supernovae, they gradually decay into other stable elements Atoms and Molecules A (not) tomos (cut) Fundamental building block of matter 3
Radioactive Decay Radioactive Decay Gamma (γ) decay Alpha (α) decay Marie and Pierre Curie (above) and Henri Becquerel (left) were awarded a joint Nobel Prize in 1903 for their discovery of radiation. Radioactive Decay Rutherford observed that matter consisted mostly of empty space. He is the father of nuclear physics. 4
Radioactive Clocks Once these elements are incorporated into a rock through deposition or crystallization, the clock is set. Knowledge (or an assumption) of the initial amount of daughter isotope coupled with measurement of the current parent/daughter ratio enables an age calculation. dn = λn where N is number of radioactive nuclei and λ is the dt radioactive decay constant. dn = λdt or loge N = λ t + loge N0 N N = N 0 exp( λt) Radioactive Decay 5
Uranium/Thorium Dating 238 U, 232 Th, 235 U primordial elements in Earth s crust λ 238 = 4.5 x 10 9 λ 232 = 1.4 x 10 11 λ 235 = 7.0 x 10 8 Clock set at crystallization (igneous rocks) or precipitation (marine carbonates) Earth Earth is an active planet and its original surface rocks no longer exist. The oldest rocks have been dated to 3.8 Ga Moon rocks have been dated to 4.2 Ga Meteorites that have struck Earth have been dated 4.5-4.6 Ga Radiocarbon Dating 14 C half life = 5,730 y Useful for once-living materials Constantly produced by bombardment of 14 N (70% of atmosphere) by cosmic rays Clock is set when organism ceases to photosynthesize/ metabolize new carbon. 6
Constructing the Geologic Time Scale Early Time Scale Based on rocks, fossils and correlations Relative Time Classification into Eons, Eras, Periods Later Time Scale Radiometric techniques applied to existing rocks Geologic Time Based on fossils, extinctions, correlations Geologic Time Based on fossils, extinctions, correlations More recent rocks have eroded less more divisions of time recently 7
Ocean Life Archean and Proterozoic Eons 3.17 billion years Most of life s history of development occurred slowly in the oceans. Primordial Soup Water on Earth s surface collected ever more complex compounds (amino acids) which were fused to proteins by lightening and UV light 3.6 billion years ago - Ga 8
Experimental Demonstration Stanley Miller (chemist) and Harold Urey (physicist) Why Water? Water is an excellent solvent. Early oceans facilitated interaction between dissolved chemicals. Living entities need some form of a solvent for biochemical reactions those that produce energy for life and water is one of the best known solvents (others may be comparable at different pressures and temperatures). Early Life Theory Membranes developed first to maintain a constant primordial soup-like microenvironment. Theory Heterotrophs probably existed first, processing non-living organic material around them. Theory - Autotrophs probably developed later, with the advantage that they could use constant energy sources (sun, hydrothermal, etc.) First life 3.6 billion years ago (Ga) 9
Harnessing Energy Photosynthesis Use of light energy (sun) and raw materials (nutrients) to grow and reproduce Chemosynthesis Use of chemical energy (inorganic compouds at hydrothermal vents) in absence of light to grown and reproduce Tube worms at a vent Earliest Cyanobacteria Stromatolites Layers of algae and sediment Evident in geologic record 3.5-3 Ga Evolution from Early Life Oxygen crisis Photosynthetic organisms filled atmosphere with O 2, after they oxidized all surface rocks 1.5 Ga after first life O 2 from water water was everywhere Ozone formation stopped UV light and formation of anaerobic bacteria s food Major extinction of anaerobes, but evolution to more efficient life (aerobic bacteria) 10
Oxygenation of Earth s Atmosphere Cambrian Explosion Cambrian Explosion 580-530 Ma 11
Reasons for the Cambrian Explosion Climate change Predation Plate Tectonics These are some theories the jury s still out Ordovician Life Sponges and bryozoans, jawless fish, corals Silurian Life Appearance of fish, continued development of Ordivician life forms in shallow inland seas 12
Devonian Life Abundance of corals and coral reefs. Land plants and amphibians, as well as land insects Carboniferous Life Very high productivity in shallow inland seas. Large coal deposits date to this period. Crinoids dominate the marine fossil record. Permian Life Abundant coral reefs, featuring sponges and clam-like animals. Large reptiles on land, paving way for dinosaurs 13
Permian Extinction 95-99% of all marine species become extinct. Land species keep diversifying and evolving. Larger than the extinction of the dinosaurs! Reasons: Conglomeration of the continents reduction of shallow seas Snowball Earth a worldwide glaciation Anoxia in the oceans Volcanic eruptions Impact event would a crater still exist? Mesozoic Sea Life Mesozoic (middle animals) Age of the dinosaurs Cenozoic Sea Life The last 65 My. Demise of the ocean lizards. Evolution of marine mammals, entering seas from land. Evolution of many modern species in concert with very old species. Mesonychid (53 Ma) Plakicetus Protocetid Ambulocetus Basilosaurus (38 Ma) 14
Summary Key Terms and Concepts Cambrian Explosion Radioactive Decay Relative Dating Oxygen Crisis Permian Extinction 15