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Bdelloid rotifers typically live in watery environments and have an incredible ability to survive. Russian scientists found the creatures in a core of frozen soil extracted from the Siberian permafrost using a drilling rig.
"Our report is the hardest proof as of today that multicellular animals could withstand tens of thousands of years in cryptobiosis, the state of almost completely arrested metabolism," said Stas Malavin, a researcher at the Soil Cryology Laboratory at the Pushchino Scientific Center for Biological Research in Russia.
Earlier research by other groups had shown that the rotifers could survive up to 10 years when frozen. In a new study, the Russian researchers used radiocarbon dating to determine that the critters they recovered from the permafrost -- ground that is frozen year-round, apart from a thin layer near the surface -- were about 24,000 years old.
It's not the first time ancient life has been resurrected from a permanently frozen habitat.
Long-dead but well-preserved mammals, including extinct cave bears and mammoths, have also been unearthed from the permafrost, which is thawing in some places as a result of the climate crisis.
Malavin said that it is highly unlikely bigger life forms could survive being frozen in this way.
"The takeaway is that a multicellular organism can be frozen and stored as such for thousands of years and then return back to life -- a dream of many fiction writers," Malavin said in the statement.
"Of course, the more complex the organism, the trickier it is to preserve it alive frozen and, for mammals, it's not currently possible. Yet, moving from a single-celled organism to an organism with a gut and brain, though microscopic, is a big step forward."
To understand how the creature survived in suspended animation in the frozen ground, the researchers froze and thawed modern day rotifers living in permafrost regions. They found that the creatures could withstand the formation of ice crystals while they were slowly frozen.
While not all the rotifers survived the freezing process, the study suggested that the creatures have some mechanism that can can shield their cells and organs from harm at very low temperatures.