BSC 2005 Lecture Notes - Lecture 8: Geologic Time Scale, Cambrian Explosion, Igneous Rock
27 Feb 2018
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Document Summary
Much of life"s history is recorded in rocks, fossils give information about the kinds of organisms that lived, what they looked like, and where and how they lived. How do we know that a fossil is a fossil: some are obvious, others are less so, specialists learn to recognize the structures and patterns of anatomical features. Not all organisms are equally likely to fossilize: remains must avoid being trampled, scavenged, or decomposed. Being buried in dry or anoxic (no oxygen) environments are best: body plan matters, hard parts>soft parts, large bones>small bones. Compares older vs. younger, no numerical age: radiometric dating: uses rate of decay of radioactive isotopes to assign numerical ages. Relative dating: the principle of superposition: in a sequence of sedimentary rocks, the oldest layer is at the bottom and the newest layer is at the top, these layers are called strata.
