Earth's Oldest Rock Crystals with Magnetic Field.

The earliest lands on earth was hot and hellish. Later, the hot lands went under new layers and got shelter. According to the researchers, there was a strong magnetic field more than 4.2 billion years ago. This research establishes the idea of finding a magnetic field that was present 750 million before the previously estimated time. The evidence of this strong magnetic field appeared 350 million years after the formation of the Earth. The Earth got protection from this magnetic field. It kept the atmosphere safe from dangerous particles from the sun. This field also was an initial base of life on earth.

The geologists have to face a lot of difficulties for the lack of proper surviving rocks. After their efforts, they found that some of the rocks belong to the Hadean period that range from 4.55 billion years ago to 4 billion years ago. But the rocks aging 3-billion-year-old from the Jack Hills of Western Australia comes with fragmentary and controversial clues. These younger rocks have tiny crystals. Researcher found presence of zircon that is a hardy mineral.  Generally, zircon chips were available in the 4.2-billion-year-old Hadean rock. But those chips were formed from cooling magma.

These crystals are also evidence of a magnetic field. John Tarduno is a geophysicist working at the University of Rochester. He is the leader of the international research team. Many researchers of the team are not ready to convince with the study results. The reason behind this is that it pushes back the accepted birth date of Earth’s magnetic field by three-quarters of a billion years. Tarduno says, “There’s been a large research group trying to prove our results wrong. That’s part of science.”

For the first time, the analysis of Tarduno and his team was published in Science in 2015. Trapped inside about two dozen zircons were even tinier grains of an iron-containing mineral, magnetite, that effectively turned each crystal into a miniscule bar magnet. As a part of the study, the team was able to find all the aligned magnetic fields by the grains. This alignment is the result of magnetic field’s cooling when the magnetite is exposed.       

The appearance of the magnetization can be noticed 4.2 billion years ago. The believes that as it is the first time when the original zircon-containing rock cooled. The results of this research would have altered if the magnetite grains got hotter. For instance, if they gained above about 600°C and cooled again the results would have changed. The scientists will fail to find the magnetic alignment. Benjamin Weiss is not agreed with Tarduno’s claims. He works at the Massachusetts Institute of Technology (MIT) as a geologist and also leads a research team. He believes that 2.6 billion years ago, there was such a heating event. He says, “These zircons have mind-bogglingly long and largely unknown histories.”     

Yesterday, Tarduno’s team came with a new evidence and revealed it in the Proceedings of the National Academy of Sciences. According to this new finding, his team says that the magnetization happened much later than the Hadean period. Zircon crystals are full of lithium ions. These ions can bleed into nearby areas by following chemical diffusion process. Tarduno’s team took consideration in three of their zircon crystals of the peripheral areas of these zones. They found a little instance of diffusion in two of the crystals. Tarduno says “It’s a sign they were never heated up above 600°C in their 4.2-billion-year history—and that their magnetic signature is original. I think that’s a remarkable finding.”

What about the remaining crystal? It showed heating signs. It had a magnetic signal which is unusually weak. Tarduno and his colleagues considered this evidence as a strangely variable magnetic field. They concluded this type magnetic field was formed 4.2 billion years ago in 2015. But now he opines that it should not be considered important anymore because of its weak signal. He also says that this particular only gained that magnetism. He also suggests that there was actually a magnetic field in Hadean period. The field had a strong churning dynamo in its core with the same capacity that operates in our present earth.   

But the new analysis does not convince all the geologists. Mark Harrison from the University of California, Los Angeles is one of them. Both high temperature and longtime duration are initial to cause chemical diffusion in the lithium ions across a boundary. He says, “If a heating incident brought the zircons above 600°C but persisted for only 10,000 years—a blink of an eye for a geologist—it would be enough time to reset the zircons’ magnetism but not to diffuse lithium. I don’t think this is even remotely smoking gun evidence,”  

Although Claire Nichols, an MIT geologist was not involved in any Jack Hills studies, she came with her own argument regarding the magnetic fields. After analyzing the rocks in Greenland, she suggests that Earth’s magnetic field was formed at least 3.7 billion years ago. In her new study, she says, “It’s great to see different research groups pushing each other to use more and more advanced techniques. It gives us the best chance of understanding the earliest record of the geodynamo.”