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Lecture12-For Web.Key Principle of superposition A typical rock formation Relative dating: some principles to follow... 1 2 Principle of original horizontality Principle of lateral continuity 3 4 Principle of cross-cutting relationships Principle of inclusions 5 6 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 100% parent and 0% daughter isotopes in the rock. The ratio of the parent and daughter • isotopes can be measured using a mass spectrometer. 7 8 Parent Daughter Method Half life Dating range isotope isotope Rubidium- Rb-87 Sr-87 47 by 10m-4.6b strontium Uranium-lead U-238 Pb-206 4.5 by 10m-4.6b Uranium-lead U-235 Pb-207 71.3 my 10m-4.6b Thorium-lead Th-232 Pb-208 14.1 by 10m-4.6b Potassium-argon K-40 Ar-40 1.3 by .1m-4.6b Carbon-14 C-14 N-14 5730 y 100-100,000 9 10 1999 GEOLOGIC TIME SCALE Paleomagnetics CENOZOIC MESOZOIC PALEOZOIC PRECAMBRIAN MAGNETIC MAGNETIC POLARITY POLARITY AGE BDY. AGE . PICKS AGE . PICKS UNCERT. AGE PICKS . N N PERIOD EPOCH AGE PERIOD EPOCH AGE EON ERA . PERIOD EPOCH AGE . AGES M M T T O O (m.y.) O (Ma) O (Ma) (Ma) S S R R (Ma) I (Ma) I (Ma) (Ma) N N H H H H (Ma) A A C C QUATER- HOLOCENE 65 .2 1 C1 0.01 30 C30 NARY PLEISTOCENE CALABRIAN 248 543 1.8 31 MAASTRICHTIAN TATARIAN 2 C2 70 C31 L 252 L 71.3 1 N UFIMIAN-KAZANIAN 2A PIACENZIAN C32 256 C2A PLIOCENE 32 KUNGURIAN 3.6 A 260 260 I 3 E ZANCLEAN 33 LATE 5 C3 5.3 CAMPANIAN 750 C33 M ARTINSKIAN 3A MESSINIAN 80 LATE C3A 269 83.5 1 R E 7.1 S SANTONIAN SAKMARIAN 4 85.8 1 E C4 900 CONIACIAN 280 282 P 4A L TORTONIAN U 89.0 1 C4A 90 ASSELIAN 10 5 TURONIAN 1000 C5 E 93.5 4 290 E 11.2 N O A . S N GZELIAN CENOMANIAN I C N S 296 N I U E 99.0 1 A 5A SERRAVALLIAN 34 C34 E KASIMOVIAN C5A E 100 300 MIDDLE V 303 L Earth has a dipole magnetic O C G M Y L 14.8 . MOSCOVIAN O S 5B C 1250 15 W R O 311 C5B ALBIAN N O I LANGHIAN Z 5C N E C5C E 16.4 A BASHKIRIAN E 110 M P . 5D EARLY 112 2 320 F I C5D N 323 O T 5E N C5E BURDIGALIAN N SERPUKHOVIAN N A 327 APTIAN I R field, with the direction in line 6 1500 P 20 C6 E E O 20.5 120 M0 P 6A 121 3 I VISEAN E S M1 B E N 1600 C6A S 340 I AQUITANIAN M3 R BARREMIAN 342 R A S 6B T C6B M5 I 127 3 S I 6C C6C 23.8 A TOURNAISIAN M M 130 C HAUTERIVIAN M10 1750 O C 7 E 132 4 C7 O with the axis of spin. 25 7A M12 354 C7A N C Y 8 CHATTIAN M14 VALANGINIAN R C8 L 360 L FAMENNIAN E M16 O 137 4 9 C9 R 364 P 140 E C BERRIASIAN FRASNIAN EARLY 10 N C10 A 28.5 370 M18 N I O 144 5 2000 11 C11 M20 A GIVETIAN 30 I T 12 G I TITHONIAN E M22 380 M 380 RUPELIAN N R 150 C12 L 151 6 LATE KIMMERIDGIAN EIFELIAN O E O 154 7 13 33.7 M25 391 V C13 T OXFORDIAN 2250 15 159 7 EMSIAN E C15 C 35 160 M29 400 400 16 C16 L PRIABONIAN I CALLOVIAN D PRAGHIAN When rocks form, they are 164 8 37.0 17 C17 S BATHONIAN 412 169 8 LOCKHOVIAN 170 MIDDLE 417 2500 S PRIDOLIAN 2500 18 S N 419 40 C18 BARTONIAN E BAJOCIAN 420 L A G LUDLOVIAN 176 I 423 N 8 19 A E WENLOCKIAN R 41.3 A C19 AALENIAN 428 permanently magnetized in the H 180 180 8 U N C E E L LATE 20 R I LLANDOVERIAN Y 2750 E T N 440 S C20 M I TOARCIAN 443 R U 45 E G N LUTETIAN A ASHGILLIAN 190 L 190 8 C L 449 J A O O 21 I P PLIENSBACHIAN N CARADOCIAN C21 O direction of the current 195 8 D E C I 458 E 460 I P EARLY 3000 3000 A L 49.0 SINEMURIAN LLANDEILIAN 22 200 A M 464 V C22 R 50 A 202 8 LLANVIRNIAN 470 E 23 HETTANGIAN O C23 P 206 8 MIDDLE H E YPRESIAN D ARENIGIAN 24 RHAETIAN 480 magnetic latitude. 210 210 8 R E 3250 C24 C 54.8 485 C O TREMADOCIAN 55 490 I NORIAN R 25 E LATE SUNWAPTAN* C25 THANETIAN * D 495 3400 N 220 STEPTOEAN* A S 221 9 500 N 500 26 E 57.9 MARJUMAN* 3500 CARNIAN A C C L 506 S C26 9 I DELAMARAN* 227 512 60 O SELANDIAN EARLY 230 R DYERAN* 27 A MIDDLE LADINIAN B 516 E 61.0 B MONTEZUMAN* C27 I 520 L 234 9 520 28 M A 3750 C28 E DANIAN ANISIAN R P 240 A A 3800? 29 242 9 65 C29 65.0 C T OLENEKIAN EARLY 245 9 30 C30 INDUAN 248 10 540 543 11 12 Plate Tectonics 13 14 15 16 Fossils 17 18 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. 19 20 Types of biases in the Taphonomy: The study of the process of fossilization, from death of the organism fossil record to discovery by the paleontologist. • 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, 21 22 Microfossils “Invertebrates” Diatoms Foraminifera 23 24 Vertebrates Stomatolites 25 26 Transitional Forms Basilosaurus hind leg 27 28 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. Tiktaalik roseae (late Devonian) 29 30 31 32 Microfossils from the Apex Chert, North Pole, Australia Stromatolite, North Pole deposits, Western Australia About 3.465 billion years old, resembling filamentous about 3.5 billion years old cyanobacteria33 34 Extant stromatolite showing closeup of cyanobacteria 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. 35 36 Eukaryotic milestones • 2.7 bya: chemical traces of eukaryotic-type lipids in fossil organic matter (controversial). • 2.1 bya: Grypania spiralis, the first fairly well- accepted fossil eukaryote • 1.6-1.8 bya: origin of single-celled algae of unknown type, known as acritarchs Grypania spiralis from Michigan 37 38 acritarch 39.
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