Are we all aliens?

The spaceship door slid open. A figure slowly emerged from the mist. As it became visible, people across the world went silent in shock. The alien was indistinguishable from a human.

We may never make contact with alien life. But if we do, aliens may look more like us than tentacled sci-fi monsters. According to a new paper published in Scientific Advances, humans might be part extraterrestrialAnything from outside Earth.. 

Humans are made up of a complex composition of chemicals. There are 21 elementsSimple substances making up everything, substances that cannot be broken down into smaller parts. in our bodies, which together form dozens of different substances.¹

One group of chemicals is peptides. These are chains of amino acidsOrganic compounds which form the basic constituents of proteins.. When joined together peptides form proteinsA kind of molecule that drives all biological processes. They make up around one-fifth of our total body mass and without them our bodies could not function. They fold into 3D shapes, making them extraordinarily complicated as a whole.: the substances that help our body stay alive. They have a huge array of functions, from fighting illness and digesting energy from food, to helping us sleep.

The new research finds that interstellar medium - the matter that makes up space between the stars - provides the perfect conditions for the creation of amino acids.² The peptides that make life possible might have formed in space then came to Earth in a meteor or a comet.

Humans have speculated about aliens ever since the ancient Greek philosopher Anaxagoras suggested that the Moon might hold life. 

If some of the raw material for life on Earth comes from space, however, perhaps we could consider ourselves aliens. The particles that allow us to exist could predate the formation of the planet itself.³

Alternatively, early lifeforms may have even arrived on Earth already living. What if our evolutionary ancestors were themselves aliens? 

We arguably act like aliens towards the planet: we exploit, reshape and damage it. Like the Martians in HG Wells' classic novel War of the Worlds (1898), we have wreaked untold damage on the Earth and used its resources for our own ends.⁴

Others find this idea absurd. Our research can only take us back so far. There is no firm evidence that we actually came from space particles.

But even if the matter that makes us came from space, we are the creatures of this planet. We are the result of the evolution, a process that takes place in Earth's unique conditions. We cannot live in any other known atmosphere. If we are not native to Earth, nothing is.

Yes: We were born in space and to space we will return. We have spacecraft. We often subjugateForcefully bring under control. other living things. Perhaps we will one day invade some poor world many light years away.

No: We might be made of cosmic particles, but we exist thanks to the combination of resources - air, water, sunlight, soil - that only Earth provides. If we are not native to Earth, nothing is.

Or... It is a matter of perspective on what is more important: raw materials or the process that ties them together. Besides, if all life derives from space dust, then all planetary life is somehow alien.