observations develop hypothesis- “untested theory” see if hypothesis can explain observed “facts”. If so, and holds up well for long time, now we have a theory. This will continue to be tested against observations/experiments.•Floatation (Archimedes) •Gravitation (Newton)•Relativity (Einstein) Life on Earth•Began quite early ~4 b.y. ago. For long time remained fairly simple in form- atmosphere consisted mostly of “poisonous” gases. •About 2.5 b/y/ ago, oxygen began to collect in the atmosphere. Some of this formed an ozone layer above the earth. •About 600 million years (m.y.) ago, life forms exploded on earth and from that time on, fossils (traces of past organisms in rocks) are common.
•Geological record shows that at particular times in the past, many life forms have gone extinct in a short period of time Mass extinction events. Causes are being investigated. •One ~ 65 m.y. ago, appears to have been caused by collision of ~ 10 km meteorite with earth. ~60% of life forms became extinct. •Another ~ 250 m.y. ago, is more enigmatic ~90% of life forms became extinct. •A third (~today) is mostly triggered by man’s actions, and could outdo the other two. •In the geological past, disposition of continents and oceans has been very different from today, thus ~200 m.y. ago, all the continents were joined together forming a super-continent- Pangaea (Fig. 2.13) •This broke up (due to plate tectonics- many divergent plate boundaries). Over the last 200 million years, created the Atlantic and Indian oceans, and pushed continents to their present positions. “Heat Engines”1.Internal- heat inside earth. Led to layering of earth and drives plate tectonics. 2.External- energy from the sun. “drives” atmosphere, hydrosphere and biosphere (Table 1.2) Principle of Uniformitarianism •“The present in the key to the past”. •Geologic processes we see today have worked in much the same way throughout geological time. •By and large geological processes have operated slowly/steadily (Fig. 1.4)•Occasionally punctuated by collision with meteorites/comets (Fig. 1.4) these have immense consequences in very short period of time. Create immense craters, global fires (burn vegetation), throw up immense gas clouds. Can radically affect global climate and cause (faunal) extinctions. Most important (Fig. 1.5)- formation of the moon.
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