Understanding a microscopic Magneto: Scientists find clues of supernova blast in fossil record

An ancient astronomical event has been frozen in time for a team of German scientists studying tiny magneto organisms.

The discovery will give insight to the composition of the dust environment of our solar system, and how the immense prehistoric cloud varies as the position of the Sun changes in the Milky Way.

There is evidence to support large impacts affecting Earth’s early climate.

Dust is, in turn, a fundamental climate regulator,” said Egli Ramon, Director of the Magnetism and Gravimetry Section of the Central Institute for Meteorology and Geodynamics (ZAMG) in Austria. “Therefore, measurements of this event on many places on Earth can provide a unique “snapshot” of the iron cycle. Interestingly, current cosmic dust deposition models predict large inputs just North of the Antarctica coast.”

Remnants of a supernova blast, in the form of iron-60, were encased in tiny specimens in the fossilized chains of magnetofossils found in Pacific Ocean sediment cores. The bacteria thrive in freshwater, brackish and marine environments. The tiny creatures produce chains of magnetic crystals inside their bodies.

These chains act as a microscopic compass, which helps them to navigate across the chemical gradient of the water column or the sediment,” Ramon said. “This “magnetic navigation”, which is called magnetotaxis, is much more efficient than the navigation of all other microorganisms, which is just based on sensing the chemicals around them. This situation is rendered by imaging that someone has to find a restaurant while walking blindfolded, only on the basis of what can be smelled in the air, instead of having a compass that gives him the right direction. Magnetotactic bacteria are thus able to rapidly find the most suited environment for them and stay there.”

The unique organisms were discovered in 1958, and scientists originally thought magnetofossils would not survive in mineral records. The tiny fossils provide key insight into ancient climate variations and also play a role in recording past variations in Earth’s magnetic field.

The bacteria are the subject of intense biological research and technical application development testing. The research stems from the ability of the tiny critters to produce near-perfect nanocrystal formations. Currently, scientists are studying how they could be used for targeted drug delivery or tissue heating in various cancer treatments. Due to the high composition of iron, the specimens give a possible glimpse into the earliest forms of life on Earth.

“There is a fascinating hypothesis that they might have originated in an iron-rich environment, such as in hydrothermal vents, where life may have started on Earth,” Ramon said.

Iron-60 is mildly radioactive, and is a type of iron supernovae expel in vast quantities. The element has a hard time forming, so any trace amounts found are usually tracked back to supernovae events.

Ramon helped locate suitable sediment cores for the study, published in the Proceedings of the National Academy of Sciences last fall. The study shows the iron-60 traces were encased in biologically produced nanocrystals of bacteria.

Just north of the coast of Antarctica, the iron-60 supply is limited by the vast distance from arid places and Earth’s continents, in turn limiting phytoplankton growth over Earth’s southern oceans.

We were able for the first time to show that magnetotactic bacteria are an important element of the iron cycles in certain types of sediment, where they process an important fraction of the total available iron,” Ramon said. “We are, of course, not claiming that the climate changes seen during the duration of this event are entirely, or even in part, attributable to cosmic dust. Climate is controlled by a large number of entangled phenomena, which make the analysis of the impact of any specific phenomenon (e.g. volcanism, large impacts, greenhouse gases) extremely difficult. Nevertheless, we have an interesting hypothesis to work on in the future.”

The supernova believed to have expelled the iron-60 is thought to have lashed out 325 light years from Earth, around 2 million years ago. The vast explosions generate massive amounts of iron-60—5 to 10 times the mass of the Sun.

The study shows that the timing of the supernova blast is extraordinarily interesting, since it lines up on the timeline of a mass extinction event of bivalves and marine snails. The time period 2.8 million years ago is also thought to be part of a global cooling period.

Timing of the blast and the evidence of the extinction in the tiny fossils leaves scientists wondering if the extinction event and the supernova blast were related.

The supernova explosion, however, was too far to have had immediate catastrophic consequences on Earth,” Ramon said. “The question remains open, whether a long-term exposure to enhanced levels of cosmic dust during the time needed for the Solar system to cross the “debris cloud” could have triggered a climate change on Earth. Our results are far from providing a definitive proof to what is at the moment only an interesting hypothesis.”

All evidence points to ancient Earth spending a great deal of time traveling through the debris of a supernova around 2 million years ago.

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