It would seem that an explosion would mix ingredients very efficiently, but the interstellar cloud was about a light year across before it began to collapse. CAIs are thought to be the first solid objects formed when the Solar System formed. However, a few CAIs have much lower ratios, so low that they may not have contained any aluminum-26 at all. This would mean that the solar nebula lasted at least several half lives of aluminum-26, or several million years, an interpretation that conflicts with other observations and theories depicting how long the solar nebula lasted. The light-green and green areas are crystals of minerals rich in both calcium and aluminum.
Red area is the surrounding rock, which consists mostly of minerals rich in magnesium and iron.
CAIs are thought to be among the very first solids to form in the solar nebula. Most have clear evidence for the presence of aluminum-26, but some have almost none. The variation means either that some formed millions of years after the others, or that aluminum-26 was not distributed uniformly in the solar nebula. The answer is important to understanding the formation of the elements, timing of events in the solar nebula, and the overall structure and chemistry of the nebula. Nichols approached the problem by searching for isotopic effects in other elements.