EARTHSC 1100 Lecture Notes - Lecture 20: James Ussher, Radioactive Decay, Radiometric Dating
3 Apr 2018
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Slide with people standing on a rock (grand canyon maybe?) The rock must be older than the people (i. e. the rock had to exist before the people could stand on it). If these humans were born say 50 years ago, then the rock (and minerals within) formed at least 51 years ago. Here we"re assuming these people haven"t left the top of this rock since they were born. Perhaps looking at the age of the trees is better because trees have roots (and hence cannot move). While you may not have observed an upright organism make these footprints, you can infer that a human must have walked across a muddy at, which then hardened to preserve the footprints. If the minerals in the mud are 1 million years old (absolute age), then the footprints were created less than 1 million years ago (relative age) Evidence: fossils found in rocks of a particular age.
