Meteoritic constraints on processes in the solar nebula

High-temperature events or processes in the solar nebula were required to form the chondrules and CAI's that make up the bulk of the substance of most chondrites. There is no consensus in the meteoritical community as to the nature of these high-temperature events or processes. In spite of this major area of uncertainty several conclusions can be reached about properties of the nebula. The chondrules and CAI's were formed in regions where the dust/gas ratio was orders of magnitude above the cosmic value. After these high-temperature objects were formed, they began to accrete very promptly (a time scale of hours, probably). Formation and aggregation of the chondrite components happened at the same radial distance in the nebula where chondrites reside today (the asteroid belt). The ambient temperature of the nebula at that time and place was relatively low ( 700 K), and was not responsible for the thermal processing of the chondrules and CAI's.