Inside our planet, the movements of large amounts of liquid iron generate the electrical currents responsible for the Earth’s magnetic field, which acts as a shield that deflects solar winds and makes life possible.
The origin of this protective envelope is still a mystery, and in recent years it has been the subject of intense debate due to the discovery in Jack Hills (Australia) of rocks containing zircon, the oldest known terrestrial material. According to some authors, these minerals present evidence of the Earth’s magnetic field, dating back to 4.2 billion years ago, almost a billion years before the date on which it traditionally originated. This fact would also suppose that the Earth’s magnetic field would have been formed almost at the same time as our own planet.
Well, now a team from the Massachusetts Institute of Technology (MIT) has turned the tables again and, in an article published in the journal Science Advances, indicates that the zircon found in the Australian deposit cannot be used as a reliable test. of the presence of magnetic field at that time.
When was the magnetic material formed?
To study the strength and orientation of the magnetic field on a given date, scientists rely on a phenomenon known as magnetization of rocks: the idea is that as a rock forms and cools, the electrons in its atoms they change their orientation in the direction of the magnetic field, but when they cool down below a certain temperature they stop moving and remain fixed. In this way, knowing the age of the rock, it is possible to deduce what the Earth’s magnetic field was like at the time it was formed.
What the new MIT work says is that even though the Jack Hill zircons are 4.2 billion years old, that doesn’t mean their magnetic material formed at the same time. To verify this, the scientists extracted more than 3,000 samples of zircon and looked for grains with signs of cracks or deposits of impurities . In this way, they were able to identify in some of these minerals the remains of another: magnetite, and discovered that it extended along cracks and other damaged areas of the zircons.
These are cracks that allow water and other elements to penetrate into the rock, so this magnetite could have settled in the zircon many years after its formation. For this reason, the authors conclude that zircon cannot be used as reliable evidence for the presence of a magnetic field 4.2 billion years ago.
Implications for the study of life history
Locating the origin of the Earth’s magnetic field is important because it could also help us better understand the conditions in which the first life forms on Earth took hold. “Life arose in the first billion years of the Earth,” explains Caue Borlina, one of the authors. “Whether or not there was a magnetic field at that time has huge implications for the environment in which those first forms appeared.”
