11.1: Proterozoic Geography
- Page ID
- 46288
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At the start of the Proterozoic Eon, most of the cratons had formed, and Earth's core had cooled sufficiently that crustal pieces weren't constantly being ripped apart by heat rising from the mantle. These Archean continents were moving, though it's unclear how closely their mechanism of movement resembled modern plate tectonics. Collisions of these ancient plates formed the supercontinent Rodinia about 1.2 billion years ago, causing the first mountain-building episode of the Appalachian Mountains. Geologists have reconstructed Rodinia by matching and aligning ancient mountain chains, assembling the continental crust pieces like a jigsaw puzzle, and using the paleomagnetic markers in rocks to orient and position the ancient continental pieces.
Laurentia and Modern Plate Tectonics
Rodinia broke up about 750 to 600 million years ago. One of the fragments was Laurentia, the continental precursor to North America. The break-up may also signal the start of modern plate tectonics, with the rigid continental crust of Rodinia breaking along rift zones and subduction forming between oceanic and continental crustal slabs. It's breakup also created many shallow-water, biologically favorable environments that fostered the evolutionary breakthroughs marking the start of the next eon, the Phanerozoic.
- Laurentia - a Proterozoic craton that forms the core of the North American continent
- paleomagnetic - ancient magnetic orientation
- Rodinia - a supercontinent that formed and broke up in the late Proterozoic
- supercontinent - a continent composed of a collection of smaller continental masses