A typical rock formation. Relative dating: some principles to follow... Wednesday, October 26, 11

Transcription

1 A typical rock formation Relative dating: some principles to follow... Wednesday, October 26, 11

2 Principle of superposition

3 Principle of original horizontality

4 Principle of lateral continuity

5 Principle of cross-cutting relationships

6 Principle of inclusions

7 Principles of unconformities (missing time)

8 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. Wednesday, October 26, 11

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10 Method Parent isotope Daughter isotope Half life Dating range Rubidiumstrontium Rb-87 Sr by 10m-4.6b Uranium-lead U-238 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 ,000 Wednesday, October 26, 11

11 1999 GEOLOGIC TIME SCALE CENOZOIC MESOZOIC PALEOZOIC AGE (Ma) EPOCH AGE PICKS (Ma) MAGNETIC POLARITY PERIOD HIST. ANOM. CHRON QUATER- NARY PLEISTOCENE MIOCENE OLIGOCENE TRIASSIC JURASSIC CRETACEOUS PERMIAN DEVONIAN ORDOVICIANSILURIAN MISSISSIPPIAN PENNSYLVANIAN CAMBRIAN* CARBONIFEROUS EOCENE PALEOCENE PLIOCENE PIACENZIAN L E L E L M E L M E E L ZANCLEAN MESSINIAN TORTONIAN SERRAVALLIAN LANGHIAN BURDIGALIAN AQUITANIAN CHATTIAN RUPELIAN PRIABONIAN BARTONIAN LUTETIAN YPRESIAN DANIAN THANETIAN SELANDIAN CALABRIAN HOLOCENE TERTIARY PALEOGENE NEOGENE 1 C1 C2 C2A C3 C3A C4 C4A C6 C6A C6B C6C C7 C8 C9 C10 C11 C12 C13 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C7A C5 C5A C5B C5C C5D C5E 2 2A 3 3A 4 4A 5 5B 5A 5C 6 6A 6B A 6C 5D 5E AGE (Ma) EPOCH AGE PICKS (Ma) UNCERT. (m.y.) MAGNETIC POLARITY PERIOD HIST. ANOM. CHRON. AGE (Ma) EPOCH AGE PICKS (Ma) PERIOD NEOCOMIAN LATE EARLY N. W. S. LATE EARLY MIDDLE LATE EARLY MIDDLE MAASTRICHTIAN CAMPANIAN TATARIAN UFIMIAN-KAZANIAN KUNGURIAN ARTINSKIAN SAKMARIAN ASSELIAN GZELIAN KASIMOVIAN MOSCOVIAN BASHKIRIAN SERPUKHOVIAN VISEAN TOURNAISIAN FAMENNIAN FRASNIAN GIVETIAN EIFELIAN EMSIAN PRAGHIAN LOCKHOVIAN PRIDOLIAN LUDLOVIAN WENLOCKIAN LLANDOVERIAN ASHGILLIAN CARADOCIAN LLANDEILIAN LLANVIRNIAN ARENIGIAN TREMADOCIAN SUNWAPTAN* STEPTOEAN* MARJUMAN* DELAMARAN* DYERAN* MONTEZUMAN* SANTONIAN CONIACIAN TURONIAN CENOMANIAN ALBIAN APTIAN BARREMIAN HAUTERIVIAN VALANGINIAN BERRIASIAN TITHONIAN KIMMERIDGIAN OXFORDIAN CALLOVIAN BATHONIAN BAJOCIAN AALENIAN TOARCIAN PLIENSBACHIAN SINEMURIAN HETTANGIAN NORIAN RHAETIAN CARNIAN LADINIAN ANISIAN OLENEKIAN INDUAN C31 C32 C M0 M1 M5 M10 M12 M14 M16 M18 M20 M22 M25 M29 M RAPID POLARITY CHANGES PRECAMBRIAN PROTEROZOIC ARCHEAN AGE (Ma) EON ERA BDY. AGES (Ma) ? LATE EARLY MIDDLE LATE EARLY MIDDLE L L M E E E E D C B A L L L M 30 C30 30 C30 C Wednesday, October 26, 11

12 Paleomagnetics Earth 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. Wednesday, October 26, 11

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14 Plate Tectonics

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18 Fossils

19 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. Wednesday, October 26, 11

20 Where is the time?

21 Taphonomy: The study of the process of fossilization, from death of the organism to discovery by the paleontologist. Wednesday, October 26, 11

22 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, Wednesday, October 26, 11

23 Microfossils Diatoms Foraminifera Wednesday, October 26, 11

24 Invertebrates

25 Vertebrates

26 Stromatolites

27 Transitional Forms Wednesday, October 26, 11

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30 Basilosaurus hind leg

31 Ankle bones of the archaeocetes Rodhocetus (Eocene) 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. Wednesday, October 26, 11

32 Tiktaalik roseae (late Devonian)

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35 Microfossils from the Apex Chert, North Pole, Australia About billion years old, resembling filamentous Wednesday, October 26, 11 cyanobacteria

36 Stromatolite, North Pole deposits, Western Australia about 3.5 billion years old Wednesday, October 26, 11

37 Extant stromatolite showing closeup of cyanobacteria Wednesday, October 26, 11

38 Proterozoic (2.5 bya to 544 mya). Evolution 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. Wednesday, October 26, 11

39 Eukaryotic 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 Wednesday, October 26, 11

40 Grypania spiralis from Michigan

41 acritarch