o Figure to be shown GET FROM BOUTTE Important example of dating U Pb method a

O figure to be shown get from boutte important

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o Figure to be shown: GET FROM BOUTTE Important example of dating: U-Pb method. a.) Age of the Earth- 4500 m.y.-based on dating of meteorites formed at the same time as the Earth b.) Explosion of life forms at base of Paleozoic occurred~550 m.y. ago c.) Faunal extinction event at Paleozoic -Mesozoic boundary occurred ~250 m.y. ago 3/7/07 K-At method d.) Faunal extinction event at Mesozoic- Cenozoic boundary occurred ~65 m.y. ago e.) Man-like creatures first appeared in East Africa~ 5 m.y. ago f.) Correct age (1925 y) obtained on ash material from Vesuvius eruption of 79 A.D. (death knoll for creationists) Radiocarbon method 39
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g.) Native Americans enter “New World”, ~ 30 k.y. ago. h.)Ice man frozen to death in the Alps ~5500 years ago i.) Cloth on which Shroud of Turin is seen, was made in about 1300 A.D. Other important geological event “dated”: 1.) Oldest rocks dated on Earth ~4200 m.y. Older record wiped out by (big) accretion event. 2.) Oldest rocks showing signs of life (algae?) on Earth ~4000 m.y. old 3.) Appalachian Mountains formed in complex series of event ~400-300 m.y. ago, when Africa and Europe “crashed into” North America 4.) Current cycle of plate tectonics began ~200 m.y. ago. Pangaea breaks up. North American from Africa and Europe at about `180 m.y. South America from Africa at about 130 m.y. 5.) India comes into hard collision with Eurasia ~50 m.y. ago. Himalayas rise rapidly in the last ~15 m.y. Big effect on world climate. Radiometric methods “work” i) Ages obtained by these methods agree with those obtained by tree-ring counting. ii) Correct radiometric age obtained for 70 AD Mt. Vesuvius eruption. iii) Radiometric ages always in right order, i.e. agree with relative dating. iv) sear-floor spreading (plate) velocities obtained from radiometric result, in excellent agreement with those obtained by modern “physics” methods e.g. measuring “distances” using laser. 40
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Unit 3 3/12/07 Chapter 7 Rock Deformation. Look at rocks I the field, we see that they can be broken ( faulted ) or bent ( folded ) by (deforming) forces. (Fig. 7-1) Faulting shows brittle behavior of rocks, folding shows ductile behavior . The latter occurs only for rocks at considerable depth inside the Earth. To understand “structures” formed by rocks in the field, we need to measure the orientation of rocks in outcrops. Measure dip and strike of beds (sedimentary rocks). Strike is a compass direction – e.g. N-S, NE-SW, whereas Dip has a compass direction as well as an angle associated with it (Fig. 7-2/3) Strike is the direction of a rock layer as it intersects the horizontal surface Dip is measured at right angles to this, and measures the amount of tilting.
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