ASB 194 lect11new.doc

ASB 194 lect11new.doc - LECTURE 11: HOW DO WE STUDY THE...

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LECTURE 11: HOW DO WE STUDY THE PAST? Animals and plants that live in the remote past all have on thing in common: they are all dead. We have to make uniformitarian assumptions (such as life forms in the past were also based on DNA replication and not some other system; organisms had the same general requirements as today) to talk about evolutionary processes and the past. In other words, our job is easier if we establish scientific principles and know when they apply. Then we can assume that certain things happened in the past even when we cant observe them. Eg. What is the easiest way to know whether apples fell to the earth in the past? 1) look for direct evidence of a fossil apple imprint in the mud and show that it's depth indicates that it fell to that spot; 2) Establish that the principle of gravity applies to all objects with mass and that gravity has always existed because the earth and apples always had mass. If we can show that apple trees existed we know that apples fell to earth even if we never find fossil evidence of that fact. Some aspects of evolution, such as evolutionary change over long periods of time (natural selection) can ONLY be studied indirectly through looking at fossil or archeological evidence. Because evolution takes such a long time (many generations) to produce observable change, such change can usually not be observed directly in nature (exception: peppered moth, but observations were made over several human generations). In order to learn how species got to be the way they are today we must study the fossil and archeological record. Paleontology : Remains of past life forms. Skeletal and other remains, [DINOSAURS] Paleoanthropology Studies of Hominids and primates--environmental reconstruction [AUSTRALOPITHECINES] Archeology : Material cultural products [ARROWHEADS] Archeological terms: Artifacts - objects produced by humans (pots, arrows) Ecofacts - remains of human activity that are not intentionally produced (eg. fire scars, pollen from collected plants, animal bones from food, etc). Here is an example including juniper berries, charred corn cobs, squash seeds, egg shells, beans, etc. Features - non-portable evidence of human activity (eg. a fire hearth, post holes from a hut, storage bins). Sites - collections of artifacts, ecofacts, features Settlement system - collections of sites on a landscape.
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HOW ARE THINGS PRESERVED? 1) Fossilization- chemical transformation of hard parts: bones teeth artifacts-- hard organic structures with a lot of inorganic material are slowly partially dissolved and replaced by inorganic minerals that do not decay. This is particularly likely in volcanic ash, limestone and highly mineralized groundwater. Most fossils are composed of calcium carbonate and silicates. Alluvial deposition environments commonly lead to fossilization. Fossils and
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ASB 194 lect11new.doc - LECTURE 11: HOW DO WE STUDY THE...

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