Why do chondrites contain both hot and cold ingredients?
Chondrites mix high-temperature chondrules and CAIs with low-temperature dust and organics, showing that materials from different places in the disc were stirred together.
Chondrites are like a cake made from ingredients prepared in very different kitchens.
Hot ingredients. CAIs formed at temperatures above about 1,300 °C, probably close to the young Sun. Chondrules formed from droplets melted at perhaps 1,400 to 1,800 °C before cooling quickly. These objects needed intense heating events.
Cold ingredients. The fine-grained matrix that surrounds chondrules contains material that never got hot. It includes presolar grains, which would have been destroyed by heating, organic molecules with isotope signatures typical of very cold environments, below about minus 200 °C, and in some chondrites, minerals that formed with water at low temperatures.
How did they mix? The disc around the young Sun was not static. Gas and dust flowed and swirled. CAIs probably formed close to the Sun and were carried outwards, perhaps by turbulence, winds or outflows. Chondrules may have formed in many places and times during the first few million years. The matrix dust was more widespread. Eventually all these components gathered together into chondrite parent bodies.
Evidence from comets. Even comets, which formed in the cold outer Solar System, contain high-temperature material. The Stardust mission found chondrule-like and CAI-like fragments in comet Wild 2 dust, showing that hot material was transported far out.
What this means. Chondrites show that the early Solar System was dynamic, with materials moving across large distances. Each chondrite group has its own mixture, reflecting where and when its parent body formed.