Sulfur and the Late Heavy Bombardment

We have no direct measure of the influx of extraterrestrial matter to Earth from 4.1 – 3.85 Ga during the late heavy bombardment (LHB). Calculations suggest that the total mass of impactors to the Moon at ca. 3.9 Ga was ~6 x 10^21 g, and that the amount of mass accumulated in the 4.4 – 4.0 Ga time frame was roughly equivalent to that which formed the major lunar basins during the LHB. The total amount of dust accumulated to the Moon during the Hadean could have been on the order of 1.2 x 10^22 g. Because evidence for the LHB epoch from terrestrial rocks is scant, all claims for a substantial role for extraterrestrial matter in the delivery of key biogenic elements such as sulfur on the early Earth must be treated with extreme caution. Marty and Yokochi (2006) estimated the total range of all extraterrestrial material (including dust and other meteoritic debris) collected on Earth's surface from 4.4 – 3.8 Ga to have been in the range of 2.4-7.2 x 10^23 g. With the average sulfur content of CM and CI meteorites as a guide, this amounts to an accumulation of about 0.8-3.6 x 10^22 g of extraterrestrial S to the planet integrated over the first 600 Myr. Although significant when compared to the cumulative mass delivered to the Moon, this amount is still ≤1% of the total S inventory for all sediments + seawater at the surface zone. Hence, terrestrial S was dominantly indigenous to the Earth since primary accretion ceased prior to ~4.4 Ga and extraterrestrial matter was, overall, a relatively minor contributor to the global S cycle to the early Earth. This is important, because mass-independently fractionated S isotopes documented in the oldest Earth rocks and minerals can with reasonable confidence be assigned an indigenous origin.