The entire planet was glued to their screens. This was the day billions had dreamt about, and billions more had feared. The first alien visitor to Earth had arrived. It had come in peace. And it was about to reveal itself to the world.

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

We may never actually make contact with alien life. But if we do, they 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. There are over 7,000 different peptides in our bodies. They have a huge array of functions, from fighting inflammationA defense mechanism of the body to fight infection, usually characterized by redness, swelling, pain, and heat in the affected area., digesting energy from food and regulating how we sleep.

The new research finds that the 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 and then arrived on Earth in a meteor or a comet.

Astronomers have already discovered that ultraviolet light from stars helps create life. Scientist Patrick Morris explains: "Starlight drives the formation of chemicals that are precursors to chemicals that we need to make life."

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.

Alternatively, early lifeforms may have even arrived on Earth complete. AstrophysicistScientists who try to understand the contents of the universe. Ethan Siegel writes: "we have yet to encounter an epochA particular time period. on Earth where our planet was devoid of life". What if our evolutionary ancestors were themselves aliens? 

Siegel suggests that the complexity of life on Earth suggests lifeforms were evolving long before the planet's own birth.³

Plus, we arguably act like aliens towards the world. 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. It is currently based on speculation, without firm evidence. Our research can only take us back so far.

And even if the matter that made our ancestors came from space, we are entirely creatures of this globe. We are the result of evolution, a process that requires Earth's unique conditions. We cannot live in any other known atmosphere. If we are not native to Earth, then nothing is.

Are we all aliens?

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 become the alien invaders of 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.

Extraterrestrial - Anything from outside Earth.

Elements - Simple substances making up everything, substances that cannot be broken down into smaller parts.

Amino acids - Organic compounds which form the basic constituents of proteins.

Proteins - A 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.

Inflammation - A defense mechanism of the body to fight infection, usually characterized by redness, swelling, pain, and heat in the affected area.

Astrophysicist - Scientists who try to understand the contents of the universe.

Epoch - A particular time period.

Subjugate - Forcefully bring under control.