Geology
Volcanic eruptions and mountain-building are active along the Ring of Fire, while in far western Alaska lava fields only a few thousand years old are common. In between lie an incomplete record of rocks from as old as 2.07 Ga years to the Holocene. A sequence of continental fragments, seafloor, and island arcs, torn, rafted, and assembled by plate tectonics, form the Proterozoic, Paleozoic and Mesozoic basement for more recent Mesozoic and Cenozoic rocks deposited on top of, and intruded into, them.
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