Did Early Earth Collide With Dark Matter? 500 Million-Year-Old Minerals Could Hold Key To Ancient Encounter

Ancient minerals buried underground could bear scars of early collisions with dark matter. Minerals such as halite and zabuyelite could serve as natural dark matter detectors, scientists said.   ( Goran Bogicevic/Alamy )

Minerals that have been buried in the Earth for half a billion years could be the key that unlocks the first piece of evidence for dark matter.

A group of physicists at the University of Michigan proposes that these minerals could hold ancient scars left over from early collisions with dark matter,

The team believes that minerals such as halite (sodium chloride) and zabuyelite (lithium carbonate) could complement the the cutting-edge dark matter detectors that engineers have built to help scientists detect dark matter.

What Is Dark Matter?

Among the mysteries of the universe, dark matter is one of the most incomprehensible. Astronomers have long been able to detect the gravitational effects of dark matter on galaxies and galaxy clusters but have failed to find direct evidence of it, even if it makes up at least 80 percent of all the matter in the universe.

The popular theory is dark matter is made up of weakly interacting massive particles (WIMPs), which interact with ordinary matter via gravity.

Sophisticated dark matter detectors are built with the goal of finding interactions between WIMPs and the nucleus of atoms such as silicon, germanium, and sodium iodide.

These detectors are buried underground to keep them from the cosmic rays that continuously stream to Earth from space. These cosmic rays interact with the materials inside the detectors, which interferes with the search for dark matter.

So far, only the DAMA/LIBRA experiment at Italy's Gran Sasso National Laboratory has claimed to have detected dark matter. However, the claims remain unverified to date.

The Science Of WIMPs

In a paper published in the preprint server ArXiv, physicist Katherine Freese of the University of Michigan says that minerals are already underground and have therefore no need to be protected from cosmic rays.

Freese and her team explain that if a WIMP collided with the nucleus of an atom, the nucleus would bounce back. The motion of bouncing back would carve a pattern into the mineral that could be anywhere from 1 to 1,000 nanometers long.

Extracting these minerals from the Earth would not prove to be too difficult, the team says, since they can use boreholes already made for geological researchers and oil prospecting companies.

The researchers would then have to break the minerals open to study the exposed surfaces and look for the telltale patterns made by nuclei bouncing back after an encounter with a WIMP.

A high-powered electron microscope or atomic force microscope could do the job. The researchers say it is also possible to use X-ray scanners or ultraviolet 3D scanners, although at lower resolutions.

If they find traces of these collisions, each mineral will likely hold various signatures owing to the multiple elements that make up a mineral. This could help scientists identify what type of WIMP was involved in the collision.

"For example, sodium chloride consists of both sodium and chlorine, so you get multiple signals from just one mineral," explains Freese. "If you do find some positive signals, then you can figure out what kind of WIMP it is based on its scattering off of sodium and its scattering off of chlorine."

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