How can I explain chondrules to pupils?

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Chondrules are tiny once-molten droplets, older than Earth, that make up much of most meteorites; comparing them to frozen raindrops or sweets in a cake helps.

Chondrules can seem obscure, but they are a lovely way to show pupils the very early Solar System.

What they are. Chondrules are round grains, usually between about 0.1 and 2 millimetres across, found in most meteorites. They were once droplets of molten rock floating in space around the young Sun. They cooled quickly, in minutes to hours, and solidified into tiny spheres. Later they were swept together with dust and other material to form asteroids. Meteorites containing chondrules are called chondrites, and they are by far the most common kind.

How old. Most chondrules formed within the first few million years of the Solar System's history, about 4.56 billion years ago, before Earth had finished forming.

Analogies. For younger pupils: imagine raindrops that froze into ice balls while falling, then got packed into a snowball. Or imagine a fruit cake, where the fruit pieces are chondrules and the cake mixture is the matrix, the fine dust that holds them together.

Seeing them. Show photographs of cut meteorite surfaces where chondrules are visible, and images of thin sections under polarised light, where they glow in colours. Real chondrites can be examined with a hand lens.

The mystery. Scientists still debate what melted the droplets. Ideas include shock waves in the gas disc, lightning-like discharges and collisions between planetesimals. This is a good example of an unsolved problem.

Activity. Pupils can make a model chondrite from plaster or clay with small beads as chondrules and metallic glitter as metal flecks.

How can I explain chondrules to pupils?

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