Scientists believe that a "significant fraction" of water molecules found on this planet are older than Earth, the solar system and even the Sun.
The study, published in Science magazine, opens up the idea that water may be found elsewhere in the universe. And, where there's water, there is life.
It's been theorised that water molecules in comet ices and terrestrial oceans first arrived in the planet-forming disk of dust and gas that travelled around the Sun some 4.6 billion years ago.
But scientists have also questioned whether water could have appeared at an even earlier stage than that.
According to Cleeves, anything between 30 and 50 per cent came from the molecular cloud, making it about one million years older than the solar system.
The University of Michigan's professor of astronomy Ted Bergin worked with Cleeves to simulate the chemistry that was sparked as the solar system was born. They looked at commonly-used water and a heavier version. Bergin said:
Chemistry tells us that Earth received a contribution of water from some source that was very cold - only tens of degrees above absolute zero, while the Sun, being substantially hotter, has erased this deuterium, or heavy water, fingerprint.
"We let the chemistry evolve for a million years - the typical lifetime of a planet-forming disk - and we found that chemical processes in the disk were inefficient at making heavy water throughout the solar system," Cleeves added. "What this implies is if the planetary disk didn't make the water, it inherited it. Consequently, some fraction of the water in our solar system predates the sun."
She said that the implications of the findings were "pretty exciting."
If water formation had been a local process that occurs in individual stellar systems, the amount of water and other important chemical ingredients necessary for the formation of life might vary from system to system. But because some of the chemically rich ices from the molecular cloud are directly inherited, young planetary systems have access to these important ingredients.
Bergin said that the simulations showed that "the formation of water from hydrogen and oxygen atoms is a ubiquitous component of the early stages of stellar birth."
He added: "It is this water, which we know from astronomical observations forms at only 10 degrees above absolute zero before the birth of the star, that is provided to nascent stellar systems everywhere." ®