Scientific method (FIG 1.1) o Make observations, do experiments. o Trying to explain phenomena or observations by developing a hypothesis o Hypothesis – untested theory
o see if hypothesis can explain observed “facts” o If hypothesis is tested and holds up well for a long time, we now have a theory o This theory will continue to be tested against more observations or experiments o FLOTATION theory – Archimedes o GRAVITATION theory – Newton o REATIVITY theory – Einstein * Life on earth o Began quite early ~ 4 billion years ago o For long time remained fairly simple in form – single-celled organisms probably b/c atmosphere consisted mostly of “poisonous” gases o About 2.5 billion years ago, oxygen began to collect in the atmosphere. e Some of this oxygen formed an ozone layer above the earth, protecting life forms from harmful incoming radiation. o About 600 million years ago life forms exploded on earth and from that time on, fossils (traces of past organisms in rocks) are common. o Geological record shows that at particular times in the past, many life forms have gone extinct in a short period of time these are caused by: Mass extinction events e Causes are being investigated so that we know if they are likely to ever be repeated * Mass extinction events o One at ~65 million years ago, appears to have been caused by collision of ~10 Km meteorite with earth. e ~ 60% of life forms became extinct (dinosaurs) o Another at ~250 million years ago, is more enigmatic (“the mother of all mass extinction) e ~ 90% of life forms became extinct o A third mass extinction going on today e Is mostly triggered by man’s actions and could outdo the other 2 * In the geological past, the disposition of continents and oceans has been very different from today. o Thus around 200 million years ago, all continents were joined together forming a super continent – PANGAEA (FIG 2.13) * PANGAEA o Broke up doe to plate tectonics – many divergent plate boundaries o Over the last 200 million years, created the Atlantic and Indian oceans, and pushed continents to their present positions o Continents are moving today * “Heat engines” – ability to do work o Internal – heat inside earth e Led to layering of earth and drives plate tectonics.
o External – energy from the sun e “Drives” atmosphere, hydrosphere, and biosphere. (atmosphere, oceans, and life) * Principle of uniformitarianism o “the present is the key to the past” e Understand processes controlling geology today and apply them to the past o Geologic processes we see today have worked in much the same way throughout geological time o By and large geological processes have operated slowly and steadily (FIG 1.4) o Steady process is occasionally punctuated by collision with meteorites or comets (FIG 1.4) e These have immense consequences in a very short period of time.