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 Principle of original horizontality Principle of lateral continuity 3 4 Principle of cross-cutting relationships Principle of inclusions 5 6 Huelsenbeck ecture 14 Slides page 1 of 11

2 1 C1 2 2A 3 3A 4 4A 5 5A 5B 5C 5D 5 6 6A 6B 6C 7 7A C2 C2A C3 C3A C4 C4A C5 C5A C5B C5C C5D C5 C6 C6A C6B C6C C7 C7A C C C10 C11 C12 C13 C15 C16 C17 C1 C1 C20 C21 C22 C23 C24 C25 C26 C27 C2 C2 30 C30 Rubidiumstrontium QUATR- NARY HOOCN PISTOCN PIOCN CAABRIAN 30 C30 31 C M0 M1 M3 M5 M10 M12 M14 M16 M1 M20 M22 M25 M2 C32 C33 C34 AT ARY AT MIDD ARY AT MIDD ARY UNCRT. (m.y.) Principles of unconformities (missing time) 7 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 100% parent and 0% daughter isotopes in the rock. The ratio of the parent and daughter isotopes can be measured using a mass spectrometer. Method Parent isotope Daughter isotope Half life Dating range Rb-7 Sr-7 47 by 10m-4.6b Uranium-lead U-23 Pb by 10m-4.6b Uranium-lead U-235 Pb my 10m-4.6b Thorium-lead Th-232 Pb by 10m-4.6b Potassium-argon K-40 Ar by.1m-4.6b Carbon-14 C-14 N y , AG HIST. MAGNTIC POARITY ANOM. CHRON. 1 GOOGIC TIM SCA CNOZOIC MSOZOIC PAOZOIC PRIOD TRTIARY PAOGN NOGN POCH AG PICKS MIOCN OIGOCN OCN PAOCN M M PIACNZIAN ZANCAN MSSINIAN TORTONIAN SRRAVAIAN ANGHIAN BURDIGAIAN AQUITANIAN CHATTIAN RUPIAN PRIABONIAN BARTONIAN UTTIAN YPRSIAN THANTIAN SANDIAN DANIAN AG MAGNTIC POARITY HIST. RAPID POARITY CHANGS ANOM. CHRON. PRIOD TRIASSIC JURASSIC CRTACOUS POCH AG PICKS NOCOMIAN MAASTRICHTIAN CAMPANIAN SANTONIAN CONIACIAN TURONIAN CNOMANIAN ABIAN APTIAN BARRMIAN HAUTRIVIAN VAANGINIAN BRRIASIAN TITHONIAN KIMMRIDGIAN OXFORDIAN CAOVIAN BATHONIAN BAJOCIAN AANIAN TOARCIAN PINSBACHIAN SINMURIAN HTTANGIAN RHATIAN NORIAN CARNIAN ADINIAN ANISIAN ONKIAN INDUAN AG PRIOD PRMIAN CARBONIFROUS DVONIAN ORDOVICIANSIURIAN CAMBRIAN* MISSISSIPPIAN PNNSYVANIAN POCH AG PICKS M M D C B A TATARIAN UFIMIAN-KAZANIAN KUNGURIAN ARTINSKIAN SAKMARIAN ASSIAN GZIAN KASIMOVIAN MOSCOVIAN BASHKIRIAN SRPUKHOVIAN VISAN TOURNAISIAN FAMNNIAN FRASNIAN GIVTIAN IFIAN MSIAN PRAGHIAN OCKHOVIAN PRIDOIAN UDOVIAN WNOCKIAN ANDOVRIAN ASHGIIAN CARADOCIAN ANDIIAN ANVIRNIAN ARNIGIAN TRMADOCIAN SUNWAPTAN* STPTOAN* MARJUMAN* DAMARAN* DYRAN* MONTZUMAN* N. W. S PRCAMBRIAN AG ON PROTROZOIC ARCHAN RA AT MIDD ARY AT MIDD 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. 12 Huelsenbeck ecture 14 Slides page 2 of 11

3 Plate Tectonics Fossils 17 1 Huelsenbeck ecture 14 Slides page 3 of 11

4 Where is the time? A fossil is any recognizable evidence of preexisting life. Types of fossils:! (1) 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 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, Microfossils Invertebrates Diatoms Foraminifera Huelsenbeck ecture 14 Slides page 4 of 11

5 Vertebrates Stomatolites Transitional Forms Basilosaurus hind leg 27 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 30 Huelsenbeck ecture 14 Slides page 5 of 11

6 31 32 Microfossils from the Apex Chert, North Pole, Australia Stromatolite, North Pole deposits, Western Australia About billion years old, resembling filamentous 33 cyanobacteria about 3.5 billion years old 34 xtant stromatolite showing closeup of cyanobacteria Proterozoic (2.5 bya to 544 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 Huelsenbeck ecture 14 Slides page 6 of 11

7 ukaryotic milestones 2.7 bya: chemical traces of eukaryotic-type lipids in fossil organic matter (controversial). 2.1 bya: Grypania spiralis, the first fairly wellaccepted fossil eukaryote bya: origin of single-celled algae of unknown type, known as acritarchs Grypania spiralis from Michigan 37 3 ndosymbiosis hypothesis for the origin of organelles Organelles originated in symbiotic union of ancestral prokaryotes acritarch 3 40 Cambrian xplosion Huelsenbeck ecture 14 Slides page 7 of 11

8 Family diversity through time Small shelly fauna from the Tommotian age Cyclomedusa (bottom-dwelling jelly fish-like creature) 45 Dickinsonia (annelid worm, cnidarian polyp?) 46 Tribrachidium (bizarre three-part symmetry; cnidarian, echinoderm?) 47 Kimberella (bilaterally symmetric; perhaps related to molluscs) 4 Huelsenbeck ecture 14 Slides page of 11

9 Aysheaia (velvet worm) Charles Walcott Burgess Shale 4 50 Pikaia (primitive chordate) Canadia (polychaete worm) Ottoia (priapulid worm) Hallucigenia (onychophoran: velvet worm) Huelsenbeck ecture 14 Slides page of 11

10 Marrella (primitive arthropod) Olenoides (trilobite) Opabinia (???) Wiwaxia (???) (five eyes and proboscis!) 57 5 What caused the Cambrian explosion? rising oxygen levels allowed larger body sizes evolution of key developmental genes evolution of skeletons (allowing larger body size) predation (arms race between predators and prey) Is the Cambrian explosion an illusion? Major phyla originated much earlier, but Cambrian/pre-Cambrian marks the passing of a taphonomic threshold. Some molecular phylogenetic analyses support an earlier divergence of phyla Huelsenbeck ecture 14 Slides page 10 of 11

11 Morphological Disparity Gould: Diversity in the Cambrian was much greater (witness the Burgess Shale Creatures), and todays diversity in body forms is a result of a perhaps random winnowing of the Cambrian diversity. Conway-Morris: Most of the Burgess Shale creatures can be placed with modern phyla Huelsenbeck ecture 14 Slides page 11 of 11