Compositional variations between chondrite groups and the inventory of shor
t-lived nuclides once present in them are consistent with an origin in the
accretion disc of a T Tauri protosun. T Tauri outbursts reprocessed infalli
ng matter, part of which was recycled back into the disc. Chondrites and ra
pidly cooled igneous meteorites together form the basis of a chronology of
events over the first 50 Myr of Solar System history. Chondrites contain ev
idence of hypervelocity impact within 2 Myr of the formation of the Solar S
ystem. This requires the local presence of a Jupiter-massed object to pump
up relative velocities. Capture of an interstellar cloudlet, which subseque
ntly underwent gravitational collapse, or of an unbound planet is implied.
Capture at a low inclination and high eccentricity would have stirred the m
atter in the accretion disc, triggered planetesimal formation and growth, s
tabilized the orbit of the proto-Jupiter, and ended the T Tauri phase of th
e protosun.