Paleogeology

Paleogeology, Paleoclimate, in relation to Evolution of Life on Earth

paleomagnetism

Paleomagnetism is used to determine Earth's ancient magnetic orientation and the orientation of rock bodies relative to the magnetic poles at the time of rock formation.

Paleomagnetic studies employ the phenomenon in which magnetic minerals, such as magnetite, record the Earth's magnetic field at the time of solidification of magma or lava (Curie temperature). [image computer simulation of Earth's magnetic field] This magnetic record of prior magnetic orientation is termed thermal remnant magnetism (TRM) for igneous and metamorphic rocks, and detrital (depositional) remnant magnetism (DRM) for sedimentary rocks in which individual grains of magnetic minerals align with the magnetic field during their deposition as sediments. Chemical remnant magnetism (CRM) can be detected in some rocks as magnetic grains are deposited from circulating solutions.

Paleomagnetism has been employed to:
● map sea floor spreading as basaltic oceanic crust spreads from its line of formation along mid-ocean ridges, providing strong empirical support for theories regarding plate tectonics as a mechanism for continental drift [diagram, magnetic stripes, ridges, ridges 2, ridges 3]
● map polar wandering
● determine past global positions of ancient rock formations or terranes (when combined with radiometric determination of the age of a rock formation)
● constraining possible ages for rocks and for geologic processes
● reconstructions of deformational histories of segments of the crust.

: e-Book Magnetic Domains to Geologic Terranes (pdf) : e-Book Lectures in Paleomagnetism (html or pdf) : paleomagnetism analyses USGS : The Geodynamo :

news and articles : Earth's Inconstant Magnetic Field (NASA) : Earth Magnetic Field Reversal : Earth's Magnetic Field Is Fading & Earth's Core Spins Faster Than Surface, Study Confirms & Magnetic Field Weakening in Stages, Old Ships' Logs Suggest & Why Does Earth's Magnetic Field Flip? & North Magnetic Pole Is Shifting Rapidly Toward Russia & "Magnetic Map" Found to Guide Animal Migration & Magnetic Beaks Help Birds Navigate, Study Says & Migrating Birds Reset "Compasses" at Sunset, Study Says & Bats Use Magnetic "Compasses" to Navigate, Study Says & Lobsters Navigate by Magnetism, Study Says & Space Dust Flooding Our Solar System & New Solar Telescope Would Focus on Sunspots, Storms National Geographic :

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