EVERYDAY SCIENCE

Detailed explanation-1: -Paleomagnetic studies of Paleoarchean lava in Australia and conglomerate in South Africa have concluded that the magnetic field has been present since at least about 3, 450 million years ago.

Detailed explanation-2: -A history of the earth’s changing magnetic field is trapped in solidified lava flows. Magnetic particles in the molten lava orient themselves toward the magnetic pole just like a compass, and when the lava solidifies, a record is preserved of the magnetic field existing at that time.

Detailed explanation-3: -The magnetism of iron-rich minerals in molten lava orients along the prevailing field, then becomes locked into place as the lava cools and hardens. “When the lava flows erupt and cool in the Earth’s magnetic field, they acquire a memory of the magnetic field at that time, ” says Singer.

Detailed explanation-4: -A freely suspended magnetic needle always rests in geographic north-south direction. Neutral points are obtained on plotting the field lines of a magnet.