What it was
A sealed box opens in a lab. You are looking at dust fetched from an asteroid, before it ever lay in Earth's rain or soil. Bennu and Ryugu gave scientists pieces of space they could handle with a cleaner trail.
Both asteroids are rich in carbon. Their grains hold organic molecules, a name for carbon-based compounds. Organic does not mean alive. Water and rock can make some of the same small parts that living cells use, without a cell doing the work.
When and where
The grains carry clues from the young Solar System. Water once changed rock inside the bodies they came from, leaving minerals behind. Spacecraft collected the samples and brought them back sealed. Teams tracked their handling so they could check what belonged to space and what Earth might add.
How we know
Bennu's dust holds salts left when briny water dried away. It also contains amino acids, small links that cells join into proteins like beads on a thread. One study found 33 kinds. Those tiny parts can survive inside a stone through a long stretch of time.
Ryugu's samples contain amino acids too. Tests also found the common nucleobases, the chemical letters cells use to store instructions. Finding those letters on separate asteroids shows that the chemistry could happen in more than one place.
Still a mystery
Nobody knows how these parts first became life. Some amino acids come as mirror twins, like your left and right hands. The samples do not give one simple left-right answer that explains life's shared choice. Nor do they prove life lived on either asteroid. The evidence in the box is chemistry.