Did you know that some of those water molecules were filtered through the trunk of an ancient tree that grew on Antarctica long before any ice covered it? Those same molecules were also once stolen by a plant that graced a hilltop on a planet that had yet to see a single flower. Before that, a mighty dinosaur drank from a pool that was once home to at least one of those molecules of water. The very first form of life, a microbe of some sort, may have been wriggling about on an effervescing hydrothermal vent as that molecule drifted through the abyssal depths of a long-forgotten sea. And billions of years ago, icy comets and soggy asteroids delivered that water molecule — and so many more like it — to a young world named Earth.

But where did all that water originally come from? Most of the matter we interact with, made from plenty of the elements on the periodic table, was forged in the cataclysmic final seconds of countless stars that had exhausted their supplies of nuclear fuel. Hydrogen and oxygen, the two atomic components of common water, aren’t rare — and after enough stars had died in our corner of the Milky Way, it’d have a decent supply of water. But how old could some of that water be? Where, and when, did the very first droplets of water in the history of the universe form?

Telescopes looking at the farthest reaches of space have found that abundances of water existed less than two billion years after the Big Bang. But a recent study, published in the journal Nature Astronomy, suggests something rather explosive: water may have been present as early as 100 to 200 million years after the universe came to be. According to the authors’ simulations, huge volumes of it were formed very close to, or at, cosmic dawn — the moment the very first generation of stars set the dark skies ablaze with light.

It's difficult to overstate just how surprisingly early to the party this water may have been. “This suggests that water, the primary ingredient for life, existed even before the building blocks of our own galaxy were formed,” says Muhammad Latif, an astrophysicist at the United Arab Emirates University in Al-Ain, and one of the study’s authors.

There are some major caveats to this research. The team didn’t detect this ancient water; they used simulations of an as-yet-unseen type of star to understand how early on that water could have formed under certain conditions. But thanks to the high fidelity of these simulations, if these primordial stars were around at cosmic dawn, then this is probably how they would have died — with a bang, and a splash. “The simulations are state-of-the-art. So yes, the results are reliable and believable,” says Mike Norman, a physicist at the University of California, San Diego who was not involved with the new research.

And if these virtual recreations of stellar self-destruction are windows into the very distant past, then that might also mean our own waterlogged, paradisiacal world is just one in a considerably long line of oceanic planets. “The dense water cores are potential hosts of proto-planetary disks which may even lead to habitable planets forming at cosmic dawn,” says Latif. “In nutshell, life could have originated much earlier than previously thought.”

Stars inevitably die, in a variety of spectacular ways, and in doing so create then scatter a multitude of elements out into space. The most violent of these deaths are associated with truly giant stars and are known as supernovas — explosions that sometimes outshine entire galaxies. Sometimes these stars simply burn through all their internal fuel reserves and implode under their own immense gravity. Other times, a voracious star eats too much of a companion star nearby and gives itself a destructive bout of thermonuclear indigestion.

Either way, supernovas produce a bevy of elements, from the lighter common ones to the rarer heavier ones. As I write this, I find myself glancing at my wedding ring. It’s made of tantalum, a blueish-silver metal. It may have been mined somewhere on Earth in the not-too-distant past, but originally, it was moulded in the heart of an expiring star — either a smaller one that had ballooned into a red giant, or a giant crucible that ignited into a supernova. That ring may be a symbol of affection in the extreme, but it’s also the shiny wreckage of a cosmic lighthouse.

Water is also a byproduct of star death but comparing it to something like tantalum might seem odd. After all, water is pretty much everywhere we look, from Earth’s oceans to the solar system’s myriad icy moons, all the way out to distant planets orbiting alien stars. In today’s universe, forming water is also quite easy: all one needs to stick two run-of-the-mill hydrogen atoms to one oxygen atom in a sufficiently cold patch of an already frigid universe. 

But it wasn’t always so effortless to keep the cosmos hydrated. Unless you formed a lot of water everywhere all at once, cosmic radiation and the high temperature conditions around exploding stars would threaten to disintegrate all those water molecules long before any seas had a chance at forming. Along with his colleagues, Latif was curious: when, exactly, was water first able to emerge? 

Naturally, their thoughts turned to the very first furnaces in the universe. Around 400,000 years after the Big Bang, the first hydrogen and helium atoms popped up before being sucked into pockets of so-called dark matter. Once in those pockets, those atoms were squashed by gravity. Eventually, they were so thoroughly compressed that nuclear fusion got going — and boom, the very first stars lit up the universe. Astronomers have decided to give these primordial stars a counterintuitive name: Population III stars. Population II stars are the descendants of Population III stars, crafted from their detritus, while newcomers like our Sun are known as Population I stars.

They may have a bit of silly name, but Population III stars are remarkably important. As Latif and his colleagues write in their recent study, these stars, and their supernovas, “were the first nucleosynthetic engines in the Universe… they forged the heavy elements required for the later formation of planets and life.” These stars were supermassive, and burned brightly and swiftly; they existed for just a few million years — not billions of years, like many contemporary stars — before blowing themselves to smithereens.

A notable point of contention is that Population III stars are theoretical. Even the almighty James Webb Space Telescope, which can see farther out in space — and farther back in time — than any other observatory, has yet to see any clear evidence (direct or indirect) of a Population III star. Perhaps one day it will. Perhaps it won’t. But the astronomical community suspect that these primordial stars, or something very similar to them, do exist at cosmic dawn. This means that, as they try to hunt them down, astrophysicists enjoy using computers to simulate their births and deaths — and what the consequences of this life cycle may be.

This recent study, which does just that, studied two Population III stars: one 13 times more massive than the Sun, and one 200 times more massive.  The smaller star burned for just 12.2 million years, while the gigantic one persisted for just 2.6 million years, explains Daniel Whalen, a cosmologist at the University of Portsmouth and one of the new study’s authors. Both end their lives spectacularly, via two slightly different types of supernova. A hail of blinding light is followed by a halo of debris rocketing out in all directions.

At first, both halos are remarkably hot — too hot for the oxygen and the hydrogen to mix. “Gas needs to be cooled down first before water can form,” says Latif. Instead, all this matter spends several million years flying out into the darkness. But after a while — 2-3 million years for the gigantic star’s supernova, and 30 million years for the smaller supernova — the debris halo becomes sufficiently chilled. The halo’s outward expansion experiences some turbulence, creating swirls that gather mass, creating gravitational traps that draw in even more mass over time. 

The oxygen and hydrogen in those dense, cold traps are now able to bond — and water begins to precipitate. If all the water from the smaller supernova was weighed, it would be equivalent to one-third of the Earth’s total mass. The gigantic supernova, which ejected far more hydrogen and oxygen, created a staggering 330 Earth-masses worth of water.

These simulations — whose stills represent resplendent, Van Gogh-like works-in-progress — are elegant. “The results are not surprising; in fact, they are to be expected. As soon as Pop III supernovae give you heavy elements, all sorts of molecules start to form in cool dense gas,” says Norman. Making multiple worlds’ worth of water would have been incredibly easy for these fast and furious stars.

Plenty of uncertainty remains, though. The typical mass of a Population III star is not yet known, which will affect their ability to manufacture water. And, lest we forget, nobody has yet scoped a Population III star. 

“Simulations that make predictions without having any observations to benchmark the models against are always difficult to fully trust. Slight tweaks to the implementation of the model could give you very different results,” says Renske Smit, an astrophysicist at Liverpool John Moores University who was not involved with the new research. “That being said, we know that dust forms very rapidly from observations around 800 million years after the big bang, so it’s not difficult to believe water could form very early as well.”

In other words: this result is big, if true. But if it is true, the consequences for the cosmos could be remarkable. These primordial stars didn’t just create a lot of water; they also released a lot of silicon, which binds with oxygen to form a very commonplace rock. In another study — currently a preprint awaiting peer-review — by the same team, models show that, just over 200 million years after the Big Bang, in the ruins of the very first stars, planets were piecing themselves together around a second generation of stellar furnaces. And those planets had access to plenty of fresh water — water that had several routes to reach them, from comet and asteroid impacts to icy dust being imprisoned within the planets as they were being built. 

Just think about that for a moment. Just a few heartbeats after the beginning of everything, of both space and time, there may have been water worlds gliding around, long before there were even enough stars to form galaxies. If life took root on those oceanic worlds, and it was able to gaze upward, it would have seen a night sky staggeringly different to our own diamantine vista.

Eventually, their own stars would have died, immolating or jettisoning them in the process. Much of the water forged by those original supernovas would have been broken down and destroyed, split into its constituent atoms. And each subsequent generation of planets, and stars, would have their own water recycled from the seas of their ancestors.

There is, however, a possibility that some of the very first water ever made, by those impossibly ancient Population III stars, is still around today. Some may be floating out in the middle of nowhere. Some may be swept up in the creation of far-flung planets. 

Not too long ago, I was outside, it was raining, and several droplets fell on my hand and trickled across my wedding ring. At that moment, a humbling thought popped into my mind. I bought that tantalum ring in 2024. That tantalum fell from space 4.6 billion years ago, along with much of Earth’s water. Those raindrops were fresh — but maybe, just maybe, a single drop contained one solitary molecule of water that was formed in the explosive final moments of a star that lived 13.6 billion years ago.

Who knows? Perhaps the next time you’re out in the rain, the memory of a star from cosmic dawn will fall on you, too.