EES-1000 Lecture 19: Lecture Notes 5
7 Oct 2016
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Uranium-238: 4. 5 billion years: so: some elements are better for dating young materials and others are better for dating very old materials! Carbon 14: 14c is often analyzed in organic remains! In this case, the clock is set when the organism dies because that is when it stops exchanging carbon with the outside world: useful for about 10 half-lives, or about 57,000 years! Other numerical dating: growth rings- annual layers from trees or shells , rhythmic layering- annual layers in sediments or ice! An erupting vent through which molten rock surfaces. A mountain built from magmatic eruptions: volcanoes are caused by tectonic activity! Volcanic materials: lava ows- molten rock that moves over the ground, pyroclastic debris- fragments blown out of a volcano, volcanic gases- vapors that exit a volcano! Controls on eruptive style: viscosity- resistance to ow, composition (sio2), temperature! Basalt (low sio2 and high t)- low viscosity lava ows away from vent!
