Solar nebula
The cloud and disc of gas and dust from which the Sun, planets, asteroids and comets formed about 4.6 billion years ago.
About 4.6 billion years ago a patch of a giant cloud of gas and dust collapsed under its own gravity. Most of the material fell to the centre and became the Sun. The rest spread into a spinning, flattened disc. This early cloud and disc are known as the solar nebula. Close to the young Sun it was hot enough for only rock and metal to survive as solids, while further out ice could form too, which is partly why the inner planets are rocky and the outer ones giant.
The solar nebula matters because everything in the Solar System, including us, is made from it. Scientists can't travel back in time, but they can study its leftovers.
Chondrite meteorites are the best record. The Allende meteorite, which fell in Mexico in 1969, contains white patches called CAIs that formed in the hottest part of the nebula about 4.567 billion years ago, the oldest dated solids we know. Allende also contains chondrules, tiny round beads of once-melted rock. Spotting these features in a cut chondrite lets you see the solar nebula's ingredients for yourself.
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Level: Explorer Ages 10 and up