Some general comments

The data gathered on chondrules and chondrites over the last two hundred years are rich and diverse. There have been evolutions in techniques and instruments and large amounts of time and energy have been spent on the study of these data. Despite this, there is uncertainty as to the origin of chondrules and chondrites and this is reflected in the great many theories for their formation. This wealth of theories and lack of consensus on any particular theory is an indication of the complexity of the processes, the rudimentary state of our knowledge about conditions in the early Solar System, and, perhaps, the absence of some key element of information about the objects themselves.

Grossman (1988) reviewed chondrule formation theories and summarized them in table form, listing 19 theories. He concluded that chondrules formed in the nebula by an unknown flash heating event. Hewins (1989) presented a very different review to that of Grossman (1988), but came to essentially the same conclusion. Boss (1996b) presented a discussion of nine chondrule formation theories (that they are impact melts, meteor ablation products, the products of a hot inner nebula, FU Orionis, bipolar outflows, nebula lightning, magnetic flares, or that they were produced in accretion shocks, or nebular shocks). He gave an uncritical listing of the pros and cons of each. On the other hand, chondrule researcher J. N. Grossman once observed in a private communication that he had counted over 60 theories for chondrule formation.