- Scientists had previously assumed that Earth’s mantle doesn’t contribute anything to planet’s magnetism.
- The new study has proved this assumption wrong.
- Iron oxide in the Earth’s mantle can retain magnetism at temperatures as high as 925°C.
Earth’s magnetic field is believed to be generated deep down (6,000 kilometers) in the planet’s core. No one has reached the center of the Earth, but researchers have been able to works out its likely structure by analyzing how shockwaves from earthquakes travel through the planet.
However, the magnetic properties of the Earth’s mantle — which has a thickness of about 2,900 kilometers and makes up 84% of planet’s volume — have been a topic of debate for years.
So far, scientists have assumed that Earth’s mantle doesn’t contribute anything to planet’s magnetism. This common assumption of a uniformly non-magnetic mantle has been questioned by recent studies.
Now, an international team of researchers has shown that hematite (a common form of iron oxide) can exhibit magnetism even in the extreme conditions of Earth’s mantle. It is mostly found beneath the western Pacific Ocean.
Analyzing the Sources Of Magnetic Fields
The Earth’s magnetic field arises due to two major sources –
- Liquid iron alloys in the deep metallic core, and
- Rocks in the outermost crust of the planet
It was assumed that rocks deep inside the Earth’s interior cannot retain their magnetic characteristics due to the extreme pressures and temperatures.
In this study, researchers analyzed the potential sources (iron oxides) of magnetic fields in the Earth’s mantle. Above a threshold temperature, these sources lose their magnetic properties.
Until now, no one has been able to properly investigate the iron oxides’ magnetism at extreme conditions found in the Earth’s interior (between 410 and 660 kilometers).
The researchers mimicked such conditions by squeezing tiny samples of hematite (found in the Earth’s mantle) between two diamonds and then heating them with lasers to achieve temperatures of over 1,000°C and pressures of up to 90 gigapascals.
Earth’s magnetic field (left) | heated samples of hematite between two diamonds (right) | Courtesy of researchers
They used a technique called Mössbauer spectroscopy to analyze the samples’ magnetism by means of synchrotron radiation. The outcomes showed that samples (iron oxides) retained magnetism at temperatures as high as 925 °C.
This clearly indicates that the previous assumptions about Earth’s mantle are not completely true: it is not ‘magnetically dead’. The findings could explain other observations of the Earth’s entire magnetic field.
Every few hundred thousand years, the geomagnetic poles of the Earth flip. The last poles flip occurred over 750,000 years ago. Scientists had previously used this data to determine Earth’s magnetic poles migrating across the Pacific. Their theories are based on the analysis of electromagnetic anomalies in the ocean floor.
This study, however, indicates those anomalies can be described by the movements of iron-oxide rocks in the Earth’s mantle beneath the West Pacific. These findings should be considered in future studies of Earth’s magnetic field as well as movements of the poles.