A meteorite that crashed into the Gloucestershire town of Winchcombe last year contained water that matched that on Earth almost perfectly.
This supports the idea that rocks from space brought important chemical components, including water, to the planet early in its history, billions of years ago.
The meteorite is believed to be the most significant recovered in the UK.
Scientists publishing their first detailed analysis say it has yielded fascinating insights.
More than 500 grams of blackened debris was picked up from people’s gardens and driveways and local fields, after a giant fireball lit up the night sky.
The crumbly remains were carefully cataloged at London’s Natural History Museum (NHM) and then loaned to teams across Europe to examine them.
Water represented up to 11% of the meteorite’s weight – and it contained a very similar ratio of hydrogen atoms to the water on Earth.
Some scientists say that the young Earth was so hot that it would have expelled much of its volatile content, including water.
That the Earth has so much today – 70% of its surface is covered by ocean – suggests there must have been a later addition.
Some say this could be from a bombardment of icy comets, but their chemistry isn’t a good match.
However, carbonaceous chondrites – meteorites like Winchcombe’s – certainly are.
And the fact that it was recovered less than 12 hours after the crash means it had absorbed very little Earth’s water, or even any contaminants.
“All other meteorites have been affected in some way by the terrestrial environment,” NHM co-first author Dr Ashley King told BBC News.
“But Winchcombe is different because of the speed with which it was picked up.
“This means that when we measure it, we know that the composition we’re looking at takes us all the way back to the composition at the beginning of the solar system, 4.6 billion years ago.
“Except for recovering rock samples from an asteroid with a spacecraft, we couldn’t have a more pristine specimen.”
Scientists who examined the meteorite’s carbon and nitrogenous organic compounds, including the amino acids, had a similarly clear picture.
This is the type of chemistry that could have been a raw material for biology to begin with on the early Earth.
The new analysis also confirms the origin of the meteorite.
Camera images of the fireball have enabled researchers to work out a very precise trajectory.
Calculated backwards, this indicates that the meteorite came from the outer asteroid belt between Mars and Jupiter.
Further investigation indicates that it was knocked off the top few feet of an asteroid, presumably during a collision.
It then took only 200,000 to 300,000 years to arrive on Earth, reveals the number of specific atoms, such as neon, created in the meteorite material by the constant irradiation of fast space particles, or cosmic rays.
“0.2-0.3 million years sounds like quite a long time, but from a geological perspective it’s actually very fast,” said NHM’s Dr Helena Bates.
“Carbonaceous chondrites have to get here fast or they won’t survive, because they’re so crumbly, so brittle, they just fall apart.”
The scientists’ first analysis, in this week’s edition of the journal Science Advances, is just an overview of Winchcombe’s properties.
Another dozen papers on specialist topics will soon appear in an issue of the journal Meteoritics & Planetary Science.
And even they will not have the last word.
“Researchers will continue to work on this specimen for years to come and unravel more secrets about the origin of our solar system,” said co-first author Dr Luke Daly of the University of Glasgow.