Continuously, for the last 33,000 years, space has been seeding Earth with a rare isotope of iron forged in super-novae.
It’s not the 1st time that the isotope, referred to as iron-60, has dusted our planet. But it does contribute to a growing body of evidence that such dusting is ongoing – we are still moving through an interstellar cloud of dust that would have originated from a supernova many-millions years ago.
Iron-60 has been the main target of several studies over the years. it’s a half-life of 2.6 million years, which suggests it completely decays after 15 million years – so any samples found here on Earth must are deposited from elsewhere, since there’s no way any iron-60 could have survived from the formation of the earth 4.6 billion years ago.
And deposits are found. Nuclear physicist Anton Wallner of the Australian National University previously dated seabed deposits back to 2.6 million and 6 million years ago, suggesting that debris from supernovae had rained down on our planet at these times.
But there’s newer evidence of this stardust – far more recent.
It’s been found within the Antarctic snow; consistent with the evidence, it had to possess fallen in last 20 years.
And, a couple of years ago, scientists announced that iron-60 had been detected in space around Earth, measured over a 17-year period by NASA’s space-based Advanced Composition Explorer.
In 2020, Wallner found more of the things , in five samples of deep-sea sediments from two locations dating back to 33,000 years ago. and therefore the amounts of iron-60 within the samples are pretty consistent over the whole period of time . But this finding actually poses more questions than it answers.
Earth, you see, is currently moving through a-region called the Local Interstellar Cloud, made from gas, dust and plasma.
If this cloud was created by exploding stars, then it’s reasonable to expect that it’s dusting Earth with a really faint rain of iron-60. this is often often what the Antarctic detection suggested; and this is what Wallner and his team were seeking to validate by examining the ocean sediments.
But if the Local Interstellar Cloud is that the source of the iron-60, there should-have-sharp increase when the solar-system entered the cloud – which, consistent with the team’s data, is probably going to possess occurred within the last 33,000 years. At the very least, the oldest sample should have had significantly lower levels of iron-60, yet it didn’t .
It’s possible, the researchers note in their paper, that the Local Interstellar Cloud and therefore the supernova debris are coincident, instead of one structure, with the debris remaining within the interstellar space from supernovae that happened many-millions years ago. that might suggest that the Local Interstellar Cloud isn’t a faint supernova remnant.
“There are recent papers that suggest iron-60 trapped in dust particles might bounce around within the interstellar space ,” Wallner said last year.
“So the iron-60 could originate from even older supernovae explosions, and what we measure is a type of echo.”
The best way to determine , the researchers note, is to seem for more iron-60, covering the gap between 40,000 years ago and around 1,000,000 years ago.
If the iron-60 abundance grows greater farther back in time, that might suggest ancient supernovae.
However, a greater abundance more recently would suggest that the Local Interstellar Cloud is that the source of the iron-60.
The research has been published in the PNAS.