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A SHOCKING new twist has been found in the mysterious case of "invincible" polar sharks that are known to live for 500 years.
Scientists believe Greenland sharks - one of the rarest species ever found - can help humans live longer lives.
Very little is known about the beast that lives under the frigid Atlantic Ocean and Arctic seas.
The sea beast can grow 23ft long, weigh 1.2 tonnes and has even been known to eat polar bears.
One shark was discovered to have lived since 1624 - the same year England declared war on Spain and founded its first Caribbean colony.
This means it has lived through the Great Fire of London, The English and American civil wars and both world wars of the last century.
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The incredibly old monster was found by a research team at the University of Copenhagen, Denmark - who concluded its age using carbon dating.
While sightings of the unique sea creatures are known to be rare since they live thousands of feet down the ocean, scientists across the world are desperately trying to crack the mystery of their long lives.
Previous research showed that their muscle metabolic activity may be an important factor that could be key to the longevity of Greenland sharks.
It follows the popular theory in biology called "pace of life" that links longevity of life to the speed of metabolic functions, LeMonde reports.
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However, a new twist being explored by researchers suggests it has to do something with the low temperatures these creatures live in.
Greenland Sharks often live in deep dark oceans where temperatures range between -1.8 degrees to 7.5 degrees.
Scientists believe living in such low temperatures slows down all chemical and biological reactions inside their bodies - and this might be the reason why they can live for so long.
Another reason experts speculate is the isolated natural habitat that is untouched by humans.
Holly Shiels, a professor in the Department of Cardiovascular Sciences at the University of Manchester, said: "They're in a place that's hard to access for humans. And they have very few natural predators other than humans. So they really can live as long as possible."
The new findings could be key to improving heart health and helping other species against climate change.
Lead researcher Ewan Camplisson, a PhD student at the University of Manchester said: “We want to understand what adaptations they have that allow them to live so long."
Research presented at the Society for Experimental Biology annual conference in Prague from Mr Camplisson showed that the metabolic activity of the species did not change as it ages, unlike other species.
He added: "Most species show variation in their metabolism when they age.
"The results support our hypothesis that the Greenland shark does not show the same traditional signs of ageing as other animals."
The scientists conducted enzyme tests on preserved muscle tissue samples from Greenland sharks and measured the metabolic activity of the enzymes.
The team found no significant variation in muscle metabolic activity across different ages, suggesting that the metabolism does not appear to decrease over time and may play a key role in their longevity.
The researchers now plan to test more enzymes and tissue types to gain an even deeper understanding of the shark’s metabolic activity.
Mr Camplisson said: "My ultimate goal is to protect the species and the best way to do this is to better understand them."
"By studying the Greenland shark and its heart, we may be able to better understand our own cardiovascular health.
“These are issues that become progressively more common and severe with increasing age.”
Researchers have already mapped out all the 16ft shark's mitochondrial DNA - genetic material held in tiny battery-like bodies in cells that supply energy.
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They hope to learn what determines life expectancy in different species including humans.
The study of its bones and tissues by the Arctic University of Norway may also provide clues about the effects of climate change and pollution over a long time span.
Five facts about the Greenland Shark
It's the world's longest-living vertebrate
Greenland sharks can live to be 400 years old or more in the deep freezing waters of the Atlantic Ocean. Scientists believe it's due to their metabolism.
Greenland Sharks can tolerate freezing temps
These beasts thrive in a frigid environment and prefer to stay in water ranging from -1 to 10°C. They are the only known shark species that can tolerate Arctic conditions all year long.
The meat of a Greenland shark is poisonous
Greenland shark meat can cause symptoms in humans similar to severe inebriation, and the neurotoxins in their flesh can even be incapacitating to sledge dogs.
Greenland shark meat is a national dish in Iceland
The dish known as Hákarl or kæstur hákarl is prepared by hanging the meat of the Greenland shark up for four to five months, removing the adverse effects of the neurotoxins.
Greenland Sharks are really big
They have been known to grow as long as 21 feet and as heavy as 1,000 kg, though the typical Greenland shark weighs around 400 kg and is about 18 to 15.7 feet long.