Researchers have been able to use an analysis of ancient rock crystals – and the magnetism records locked inside them – to trace back the history of Earth's inner core across hundreds of millions of years.
Earth's core, a dense hot blob of iron and nickel, is actually made up of two layers – the solid inner core crammed inside a molten outer core. Then comes the rocky mantle and the crust that we all live on. We're talking about 2,900 kilometers underground.
Based on the researchers' findings, it seems Earth's inner core was crystalizing into a significantly large mass around 550 million years ago. This crystalization provided enough heat to restore the magnetic field – which had depleted around 15 million years earlier – and setting the scene for a majorEarth's magnetic field, protecting life from harmful solar winds, is actually governed by the swirling liquid iron in the outer core.
The huge distances and hot temperatures make measuring Earth's core virtually impossible, so scientists rely on crystals in rock – in this case, feldspar crystals inBy comparing rocks dated at 565 million years ago to rocks dated to 532 million years ago, the team was able to see the shift in magnetic strength – a dramatic comeback for Earth's magnetic field. The change took tens of millions of years, but that's relatively speedy in terms of geological timescales.
Thermal models based on the research suggest that the structure of the inner core changed around 450 million years ago, creating a boundary between the innermost and outermost inner core.
Knowing more about how the inner core evolved to its present state can also teach us about how it might change again in the future – as well as giving us a comparison point to use when studying other planets.to see what would have happened if the inner core hadn't grown and provided the impetus for Earth's magnetic field to be made strong enough to repel harmful solar radiation from the surface.
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