The Solar System Timeline

Existing dates for early Solar System materials suggests that calcium-aluminium inclusions, CAIs, mm-sized, irregular high temperature grains in meteorites, are the oldest, first formed materials. Chondrules, which are mm-sized melted droplets, found with CAIs in primitive meteorites, seemed to have formed later, perhaps even 2 million years later than CAIs. This difference in age raises many difficult questions. Just how did CAIs survive for 2 million years when they are so easily swept into the early Sun? Were CAIs stored somewhere for all this time, and if so how did CAIs and chondrules end up in the same asteroids? Did the Sun's disk of gas and dust, the Solar Nebula, really survive for at least 2 million years, when so many other young stars lose their disks much quicker?

Recent dating on differentiated meteorites, from asteroids that melted, are even more of a puzzle, since some of these appear to be older than chondrules. If primitive meteorites really are primitive, if they are the primordial building blocks of planets and asteroids, then how can their chondrules have formed after other asteroids had melted?

The problem with the ages of early Solar System objects is fundamental. Was there really a Solar System timeline, in which one event followed another in an orderly fashion, or did various events happen at the same time, but just in different places in the early Solar System. The answers to these questions are crucially important if we are to understand how the Solar System as a whole came into being.

Measuring using Different Clocks

The problem with dating the early Solar System is there are too many different clocks. Because the formation of the Solar System happened 4.5 billion years ago such high-precision analyses of radioactive decay products are needed that dates can be inaccurate. Different rocks also need different radioactive decay "clocks" to be used and how to relate one to the other is not fully understood. When the length of time is so large, even small differences are highly significant.

The most precise ages come from short-lived radionuclides, that have now almost completely decayed, but were present in abundance in the early Solar System. 26-aluminium has been the most widely used, but now is thought to have been generated, at least in part, in the inner Solar Nebula, and might not give reliable ages. Even other short-lived clocks, like 53-manganese and 187-hafnium, might be affected if these isotopes were not evenly mixed in the nebula. All short-lived clocks also suffer from the same problem, they only give dates from the "beginning" of the Solar System, and so long-lived radioactive decay "clocks" such as uranium-lead are needed to give ages to their dates.

The Origin Network is testing whether these different radioactive dating techniques really do agree by high-precision analyses of these isotopes in the same early Solar System samples.

Analysis Answers