Two newly found pockets of gas contain only original elements created minutes after the universe's birth.
The Big Bang theory proposes that only the lightest elements were formed just after the birth of the universe.
No such pristine samples had ever been found until now.
Pockets of primordial gas may have played a role in funneling matter into galaxies for star formation.
Scientists have found two interstellar clouds of original gas, which -- unlike everything else in the universe -- has never mingled with elements forged later in stars.
The existence of pristine gas that formed minutes after the Big Bang explosion some 13.7 billion years ago, had been predicted, but never before observed.
The clouds, which are located about 12 billion light-years from Earth within the constellations Ursa Major and Leo, were found serendipitously during an ongoing study to characterize gas in distant galaxies.
In analyzing the light coming from quasars (active nuclei of distant galaxies), astronomers realized the rays had passed through gas that contained only hydrogen and deuterium, elements that formed minutes after the Big Bang.
The surprise was that the clouds contained nothing else -- no carbon, no nitrogen, no silicon, no iron -- none of the heavier elements forged in stars and spread throughout the universe.
"In some respect we were searching for this, but we had been doing so for years and had been unsuccessful so the discovery was a very welcome surprise," astronomer Jason Prochaska, with the University of California's Lick Observatory, told Discovery News.
One of the foundations of the Big Bang theory is that only the lightest elements -- hydrogen, helium, lithium and the hydrogen variant deuterium -- formed minutes after the universe's creation, but no such pristine samples had ever been found.
"These two clouds are the first examples to fit precisely in that picture," Prochaska said.
All other elements were made inside of stars millions and billions of years later.
"One of our biggest questions in cosmology is how galaxies get the gas they need to form stars, and how they also sent out the remnants of stars into their surroundings," physicist John O'Meara, with Saint Michael's College in Vermont, told Discovery News.
"These clouds offer important insights into how galaxies get and return gas into their environments," he said.
The research appears in this week's Science.