Principle of original horizontality Principle of lateral continuity

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1 A typical rock formation Principle of superposition Relative dating: some principles to follow... 2 Principle of original horizontality Principle of lateral continuity Principle of cross-cutting relationships Principle of inclusions 6

2 C 2 2A A A A B C D 6 6A 6B 6C A C2 C2A C CA C CA C CA CB CC CD C C6 C6A C6B C6C C CA C C C0 C C2 C C C6 C C C C20 C2 C22 C2 C2 C2 C26 C2 C2 C2 0 C0 Rubidiumstrontium QUATR- NARY HOOCN PISTOCN PIOCN CAABRIAN 0 C0 C C2 C C AT ARY AT IDD ARY AT IDD ARY UNCRT. (m.y.) Principles of unconformities (missing time) Radiometric Age Dating Uses unstable isotopes of naturally occurring elements. The isotopes decay: they change into different elements or different isotopes of the same element. The rate of decay is known (has been measured in the laboratory) for a variety of isotopes. When igneous rocks form, there is 00% parent and 0% daughter isotopes in the rock. The ratio of the parent and daughter isotopes can be measured using a mass spectrometer. ethod Parent isotope Daughter isotope Half life Dating range Rb- Sr- by 0m-.6b Uranium-lead U-2 Pb-206. by 0m-.6b Uranium-lead U-2 Pb-20. my 0m-.6b Thorium-lead Th-22 Pb-20. by 0m-.6b Potassium-argon K-0 Ar-0. by.m-.6b Carbon- C- N- 0 y 00-00,000 0 AG HIST. AGNTIC POARITY ANO. CHRON. GOOGIC TI SCA CNOZOIC SOZOIC PAOZOIC PRIOD TRTIARY PAOGN NOGN POCH AG PICKS IOCN OIGOCN OCN PAOCN PIACNZIAN ZANCAN SSINIAN TORTONIAN SRRAVAIAN ANGHIAN BURDIGAIAN AQUITANIAN CHATTIAN RUPIAN PRIABONIAN BARTONIAN UTTIAN YPRSIAN THANTIAN SANDIAN DANIAN AG AGNTIC POARITY HIST. RAPID POARITY CHANGS ANO. CHRON. PRIOD TRIASSIC JURASSIC CRTACOUS POCH AG PICKS NOCOIAN AASTRICHTIAN CAPANIAN SANTONIAN CONIACIAN TURONIAN CNOANIAN ABIAN APTIAN BARRIAN HAUTRIVIAN VAANGINIAN BRRIASIAN TITHONIAN KIRIDGIAN OXFORDIAN CAOVIAN BATHONIAN BAJOCIAN AANIAN TOARCIAN PINSBACHIAN SINURIAN HTTANGIAN RHATIAN NORIAN CARNIAN ADINIAN ANISIAN ONKIAN INDUAN AG PRIOD PRIAN CARBONIFROUS DVONIAN ORDOVICIANSIURIAN CABRIAN* ISSISSIPPIAN PNNSYVANIAN POCH AG PICKS D C B A TATARIAN UFIIAN-KAZANIAN KUNGURIAN ARTINSKIAN SAKARIAN ASSIAN GZIAN KASIOVIAN OSCOVIAN BASHKIRIAN SRPUKHOVIAN VISAN TOURNAISIAN FANNIAN FRASNIAN GIVTIAN IFIAN SIAN PRAGHIAN OCKHOVIAN PRIDOIAN UDOVIAN WNOCKIAN ANDOVRIAN ASHGIIAN CARADOCIAN ANDIIAN ANVIRNIAN ARNIGIAN TRADOCIAN SUNWAPTAN* STPTOAN* ARJUAN* DAARAN* DYRAN* ONTZUAN* N. W. S PRCABRIAN AG ON PROTROZOIC ARCHAN RA AT IDD ARY AT IDD ARY BDY. AGS ? Paleomagnetics arth has a dipole magnetic field, with the direction in line with the axis of spin. When rocks form, they are permanently magnetized in the direction of the current magnetic latitude. 2

3 Plate Tectonics 6 Fossils

4 Where is the time? A fossil is any recognizable evidence of preexisting life. Types of fossils:! () Trace fossils! (2) Preserved material Fossils are our only direct evidence of what organisms looked like in the past. The fossil record is a biased one. 20 Taphonomy: The study of the process of fossilization, from death of the organism to discovery by the paleontologist. Types of biases in the fossil record Fossils with no hard parts are rarely preserved. Fossil record is mostly a record of shells and bones. Organisms that lived in areas where they are likely to be preserved. Time averaging of fossil beds. Post-mortem transport, scavenging, 2 22 icrofossils Invertebrates Diatoms Foraminifera 2 2

5 Vertebrates Stomatolites 2 26 Transitional Forms Basilosaurus hind leg 2 2 Ankle bones of the archaeocetes Rodhocetus (ocene) on the left, a pronghorn (middle) and Artiocetus (right). Note the double-pulleyed astragalus. Other features in common are a notched cuboid and a prominent fibular facet. Tiktaalik roseae (late Devonian) 2 0

6 2 icrofossils from the Apex Chert, North Pole, Australia Stromatolite, North Pole deposits, Western Australia About.6 billion years old, resembling filamentous cyanobacteria about. billion years old xtant stromatolite showing closeup of cyanobacteria Proterozoic (2. bya to mya). volution of organisms with oxygenic photosynthesis caused an increase in oxygen levels. Rising oxygen levels in the world s oceans caused the formation of iron oxide, often preserved in the banded iron formation. 6

7 ukaryotic milestones 2. bya: chemical traces of eukaryotic-type lipids in fossil organic matter (controversial). 2. bya: Grypania spiralis, the first fairly wellaccepted fossil eukaryote.6-. bya: origin of single-celled algae of unknown type, known as acritarchs Grypania spiralis from ichigan acritarch