What can meteorites tell us about the early Solar System?
Meteorites act as a time capsule, recording when the first solids formed, how quickly asteroids and planets grew and melted, which stars contributed material, and how water and carbon compounds were spread around.
Earth has recycled almost all of its earliest rocks through plate tectonics, erosion and melting. Meteorites, mostly from small bodies that cooled long ago, preserve evidence that our own planet has erased. First, they give us a timeline. Calcium-aluminium-rich inclusions, dated to about 4.567 billion years, mark the start of Solar System history. Chondrules followed within a few million years. Iron meteorites show, through the hafnium-tungsten dating method, that some asteroids had already melted and formed metal cores within just a million or two years. Planet building was therefore remarkably fast.
Second, they reveal the heat source. Many meteorites contain traces of magnesium-26 produced by the decay of aluminium-26, a short-lived radioactive isotope. Its decay released enough heat to melt the earliest-formed asteroids, explaining why some became layered worlds with crusts and cores while later-forming bodies stayed as unmelted chondrites.
Third, they record where material came from. Presolar grains, specks of stardust older than the Sun, show that dying stars contributed dust to the cloud that formed the Solar System. Subtle isotopic differences split meteorites into two broad families, carbonaceous and non-carbonaceous, which many researchers interpret as material that formed in the outer and inner Solar System, possibly kept apart for a time by the early growth of Jupiter.
Fourth, they show how water and organic compounds were made and moved. Carbonaceous chondrites contain minerals formed in liquid water and a rich mix of organic molecules, including amino acids, supporting the idea that asteroids helped supply young Earth with life's raw materials. Each new technique, and each sample-return mission, adds detail to this picture of the Solar System's first few million years.