Besides the rusting hull of a majestic British superliner and a few stray seashells, you never know what you'll end up finding at the bottom of the ocean if you look hard enough. If you're lucky, you could even discover the leftovers of a cataclysmic stellar explosion from millions of years ago embedded in the stratified dirt of the Pacific Ocean. A persistent European scientist has now detected the presence of a unique isotope buried in the waterbound sands and sediment which point to the particled remains of ancient supernovae. Iron-60 (60Fe) is one of the most notorious heavy elements produced by supernovae when they explode, projecting those elements into the depths of outer space.
Due to 60Fe’s short half life, it should actually be absert on Earth, but faint traces have been revealed deep in the ferromanganese crust of the ocean floor's microfossil record.
Astrophysicist Shawn Bishop of the Technological University in Munich has been hunting down this ultra-rare isotope for ten years and has now concluded his findings (originally theorized back in 2013) in a new report published in the Proceedings of the National Academy of Sciences (PNAS). According to the paper, a supernova blast over 2.2 million years ago has deposited its fingerprints inside this deep sea sediment, rich with the imprint of long-dead bacteria.
Here's how the theory breaks down in a Scientific American piece from 2013:
Bishop thinks it’s possible that fine-grained debris from a supernova explosion could pass through Earth’s atmosphere, rapidly oxidizing in the process so that they are broken down into tiny nano-oxides. These would rapidly dissolve in oxygen, form rust, and eventually settle in the sediment along the ocean floor, where the bacteria would suck them up for their crystal chains. When the bacteria eventually die, those chains remain behind in the sediment, and 60Fe would be locked inside. So any traces of 60Fe found in that sediment would constitute a kind of biogenic signature of a supernova event, preserved in the fossil record.
Bishop's seafloor sleuthing originated from research postulated back in 1963 by Italian microbiologist Salvatore Bellini, who noticed these specific bacteria could steer themselves toward the North Pole via invisible magnetic fields to assist in navigating themselves by these internal crystals to desirable low-oxygen environments.
So next time you build that sandcastle replica of Game of Thrones' Red Keep, it just might contain flakes of fossilized stardust.