2011-06_Foss - EVOLUTION (11:704-486) FOSSIL RECORD SMOUSE...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
EVOLUTION (11:704-486) – FOSSIL RECORD S MOUSE – SPRING 2011 1 T HE F OSSIL R ECORD Geological Fundamentals: As I mentioned earlier, it is difficult to see deep into the tree of life, if we only have the existing (now time-depth) cross-cut of specimens. Imperfect as it is, the fossil record provides us with the clues that tie it all together. We end up with both locational and temporal information about the ancestral forms that existed, but to decipher that information, we need to start with a bit about the geological processes that have operated. Rock Formation – Rocks formed at the earth’s surface originated as molten material (magma), extruded from deep within the earth. Under intense heat and pressure, extrusion is explosive, via volcanoes, but most rock is formed as crustal rock, pushed up from below. Rock formed in this fashion is called igneous . If it erodes and is deposited elsewhere, it becomes sediment – elsewhere. Under pressure, sediment becomes sedimentary rock. With enough heat and pressure, both igneous and sedimentary rock become metamorphic . Most fossils are found in sedimentary rock, never in igneous or volcanic rocks. A few fossils are found in other situations, archaic humans in peat deposits, saber tooth tigers in tar pits, mammoths in frozen ice or tundra, insects in amber, and so on. Over 250,000 fossil species have been defined, a very tiny fraction of the species that have ever been there. In other words, those things that either wash down in the runoff and are deposited in the local catchment, which might be the continental shelf in some areas, or things that sink to the bottom and get covered in silt, could possibly end up as fossils, but most critters die and get consumed, being utterly biodegradable. The probability of becoming a fossil is very small, but we’ve had 3.5 billion years and a planet to work with, and it has happened, now and then. Plate Tectonics – Alfred Wegener first posited the idea that the continents drifted around on the surface of the earth’s core in 1915, but his idea wasn’t taken seriously until the 1960s, when both definitive evidence for and an explanation of the phenomenon was forthcoming. The surface crust, the lithosphere , includes both the continents and the crust, below the oceans, is now known to consist of 8 great plates and some minor ones, which move across the planet. Figure 6.1. Futuyma. Page 128
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
EVOLUTION (11:704-486) – FOSSIL RECORD S MOUSE – SPRING 2011 2 At certain points, within the asthenosphere , the heat of the earth’s core sets up convection cells, and magma rises to the surface, cools and spreads out, pushing the plates away from the rift . The mid-Atlantic ridge is such a spot. The plates move apart at 5-10cm a year. The rift valley in Eastern Africa is another such zone.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 08/18/2011 for the course ECOLOGY 301 taught by Professor Staff during the Spring '11 term at Rutgers.

Page1 / 8

2011-06_Foss - EVOLUTION (11:704-486) FOSSIL RECORD SMOUSE...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online