Scientists have confirmed the existence of a powerful magnetic field of the Earth has 4.2 billion years ago, in the oldest geological era — Katara. This became known thanks to a detailed study of ancient inclusions of zircon crystals, discovered in the depths of ridge of the Jack hills in Australia. Before this study it was considered that it is impossible to obtain reliable information about the magnetic field over 3.4 billion years. The work, published in the Proceedings of the National Academy of Sciences, will help to understand the evolution of the core of the planet and its atmosphere, which is important for the study of the origin of life on Earth.
In the core of the Earth continuously flow convective flows of molten metal, working as a natural magnetic field generator, — magnetic Dynamo. Magnetic field reflects the solar wind, without which the planet’s atmosphere would gradually be blown away and the water was split into oxygen and hydrogen. Pure hydrogen, being very light, poorly maintained gravity and gradually disappears into space. Thus, no magnetic field on Earth would be unable to retain water and support life.
Usually the history of the earth’s magnetosphere is studied by residual magnetization of ancient rocks. Body gain induction when placed in a magnetic field, but some materials can keep the inductance after the external field disappears. Measuring this residual inductance, it is possible to calculate the characteristics of the field that gave it birth. The problem, however, is that the oldest available for the study of rocks contain information no older than 3.4 billion years: the previous data is deleted by the geological metamorphoses, especially the excessive heating in the earth and chemical changes.
In order to circumvent this limitation, you can explore ancient inclusions has not changed the minerals in the younger sediments. This method has significant limitations, including the number of such inclusions in the sample must be very large, and they must be arranged in a common dense domain.
Zircon is the most attractive mineral for this analysis because it is highly stable and the time of formation is easy to date. Suitable for this method of research samples has been found in geological outcrop discovery in the ridge of Jack hills, Australia. The old grains of zircon from there was formed 4.2 billion years ago and store information about that era.
Critics of this method arguethat a significant part of the magnetization was found in samples of secondary and formed after the deposition of crystals of zircon in the rock. They found in crystals of micro-inclusions of magnetite and traces of relatively young cracks through which, in their opinion, he got in, and suggested that the magnetic trace of zircon from the Jack hills contaminated with these later inclusions. Opponents also doubted the possibility of separating the residual induction of the crystals on the induction of the surrounding quartz.