Radiometric dating of surface rocks

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Extrusive igneous rocks are formed from magma that cools and solidifies at or near the Earth’s surface.Exposure to the relatively cool temperature of the atmosphere or water makes the erupted magma solidify very quickly.The smallest grains are called clay, then silt, then sand.Grains larger that 2 millimeters are called pebbles.They form from deposits that accumulate on the Earth's surface.Sedimentary rocks often have distinctive layering or bedding.Intrusive igneous rocks are formed from magma that cools and solidifies deep beneath the Earth’s surface.

Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot, mineral-rich fluids or, more commonly, some combination of these factors.Rapid cooling means the individual mineral grains have only a short time to grow, so their final size is very tiny, or fine-grained Sometimes the magma is quenched so rapidly that individual minerals have no time to grow.This is how volcanic glass Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms.Igneous rocks form when molten rock (magma) originating from deep within the Earth solidifies.The chemical composition of the magma and its cooling rate determine the final igneous rock type.

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