Lecture 3 (September 4)

Lecture 3 (September 4) - Lithosphere: plates- upper layers...

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Lithosphere: plates- upper layers of Earth slides around a top o Continental Lithosphere Thicker ( > 100 km thick, passing up to > 300 km thick in some places) Mainly composed of relatively low density granitic type rocks (rich in silica and aluminum) Because its less dense, its buoyant o Oceanic Lithosphere Thinner (usually about 100 km thick) Composed of mafic and ultramafic rocks (rich in iron and magnesium) Because its denser, less buoyant Aesthenosphere: weak, “slushy” layer beneath, not molten Earth o 4.6 billion years old (Ga) o Oldest rocks: 3.8 billion years old (e.g. Greenland, South Africa, and Australia) o Oldest mineral grain (i.e. a piece of a rock): 4.2 Ga (Australia) o Continents are much older than oceans o Oldest parts of the ocean: 2 million years old (Ma, millions of years ago) oceanic lithosphere constantly being subducted and reformed at ridges Radiometric Dating o Based on decay at known rates of naturally occurring radioactive minerals
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Lecture 3 (September 4) - Lithosphere: plates- upper layers...

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