A professor from Stanford University has claimed that aliens have been on planet earth for some time.
It's a question which has long plagued the minds of many, from academics to conspiracy theorists, do aliens exist?
There are numerous theories out there about whether we are alone in the universe.
One suggests that although other intelligent civilisations are certain to exist, the universe is too vast and life too fleeting for two such civilisations to ever cross paths.
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There's also the theory that the universe is teeming with intelligent life, but owing to our greed, selfishness, and destructive impulses, we are being galactically snubbed.
However, one man is convinced that not only do extraterrestrial life forms exist, but they are '100%' living among us even now. Dr Garry Nolan is a professor at Stanford University School of Medicine, and has also worked on US government programmes dealing with UFOs.
He spoke at a conference in Manhattan last week called The Pentagon, Extraterrestrial Intelligence and Crashed UFOs, where he claimed that aliens are living among us right now.
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He said: "I think it's an advanced form of intelligence that using some kind of intermediaries. It's not that they walk among us wearing a skin suit. You're going to put something there that I think of as an intelligence test."
The professor added: "They're showing up and saying who amongst you are intelligent enough to realize what it is you're looking at. 'Can you see what's in front of you for what it really is? Can you see the anomalous data point?"
Nolan went on to speak about his 'personal experiences' of people working on trying to reverse engineer 'downed crafts'.
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He said: "A tiny piece of knowledge from that could revolutionize what we're doing."
Nonetheless, he said he does not think that aliens will come to Earth to harm us.
He said: "I'm not worried about them coming and raiding us or taking our women and children. That's not my concern. My concern is how do we use it."
The search for extraterrestrial life has seen a resurgence in recent years. One group of scientists at the University of California has said they think that extraterrestrials could make contact with humans as soon as 2029.
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One possible location for extraterrestrial life is actually within our own solar system.
Scientists at NASA have said it is likely that Europa, a moon of Jupiter, has an ocean beneath a frozen layer of ice 10 to 15 miles think. The ocean itself could be 40 to 100 miles deep.
Given that we know life exists on Earth in the deep ocean completely independent of the Sun's energy, it is entirely possible that these oceans contain life forms which have evolved to survive in conditions not unlike those in our deepest, darkest oceans.