The Earth was formed about 4.6 billion years ago. The oldest rocks of the Earth were found at the Jack Hills, Australia. In the past, estimates were made of the strength of the Earth's magnetic field using zircon crystals older than 4 billion years that were found there. However, it is suspected that these estimates were affected by heating and metamorphism after zircon crystallization, so their reliability is open to question.

Collaborative research between AIST and the University of Rochester, the University of Liverpool, the Geological Survey of Canada, the University of Manitoba, the U.S. Naval Research Laboratory, the University of California at Santa Cruz, Curtin University, the University of Wisconsin-Milwaukee, and Michigan Technological University, has shown the likelihood that the Earth had a magnetic field about 4.2 billion years ago. By using SQUID magnetic microscopy and other advanced analytical techniques, the researchers have shown with a high degree of certainty that this magnetic field was recorded in zircon crystals that were formed immediately after the formation of the Earth. The crystals were found at the Jack Hills in Western Australia. The appearance of a sufficiently strong magnetic field immediately after the Earth’s formation makes it possible to narrow down the Earth’s internal structure and its geodynamo during that period. The Earth’s magnetic field prevented the atmosphere from being stripped away by the solar wind and thus has important implications for the evolution of Earth's atmosphere and life. Highly sensitive analysis of the magnetic field recorded in geological samples using SQUID magnetic microscopy is expected to contribute further to the constraints on the Earth’s environmental conditions at the time.