Researchers find oldest undisputed evidence of Earth’s magnetic field

Iron particles effectively act as tiny magnets that can record both magnetic field strength and direction when the process of crystallization locks them in place. The researchers found that rocks dating from 3.7 billion years ago captured a magnetic field strength of at least 15 microteslas comparable to the modern magnetic field (30 microteslas). Image credit: Claire NicholsUnderstanding how Earth’s magnetic field strength has varied over time is also key for determining when Earth’s inner, solid core began to form. A significant challenge in reconstructing Earth’s magnetic field so far back in time is that any event which heats the rock can alter preserved signals. This allowed the researchers to build a clear body of evidence supporting the existence of the magnetic field 3.7 billion years ago.