#palaeomagnetism

[kamalkafir-blog]

Invariance of dynamo action in an early-Earth model

Tarduno, J. A. et al. Geodynamo, solar wind, and magnetopause 3.4 to 3.45 billion years ago. Science 327, 1238–1240 (2010). ADS  CAS  Google Scholar  Biggin, A. J. et al. Palaeomagnetism of Archaean rocks of the Onverwacht Group, Barberton Greenstone Belt (southern Africa): evidence for a stable and potentially reversing geomagnetic field at ca. 3.5Ga. Earth Planet. Sci. Lett. 302, 314–328…

[a2geographyprocrastination]

1. Plate Movement - Sea floor spreading and Paeleomagnetism

Sea floor spreading was discovered when the mid atlantic ridge was discovered and studied.

Evidence for this was the alternating polarity of rocks in the earth's crust either side of the mid atlantic ridge.

Iron particles in the lava that erupts from an ocean ridge are aligned with the Earth's magnetic field. when the lava solidifies, these iron particles create a permanent record of the earth's polarity at the moment that piece of crust was created. This is called Palaeomagnetism. since the Earth's polarity reverses approximately every 400,000 years, a series of magnetic stripes.

These "stripes" are mirrored of either side of the ocean ridge, and therefore suggest that the ocean crust is spreading away from this boundary as new crust is being created.

Since new crust is being created and yet the Earth is not getting bigger, crust must also be being destroyed it accomodate for the new crust created at the ocean ridges. this destruction of the earth's crust occurs at ocean trenches, where one plate is being pulled under another. this is called Subduction.