Previous studies of limestone beds of mid-Ordovician age from both
Sweden and China show that the Earth saw an at least two orders of
magnitude increase in the influx of extraterrestrial material
approximately 470 Ma, following the disruption of an L-chondrite parent
body in the asteroid belt. Recovered extraterrestrial material consists
of fossil meteorites and sediment-dispersed extraterrestrial chromite
(SEC) grains, both with L-chondritic origin. Ne isotope analysis of SEC
grains from one of the Swedish limestone sections revealed that the vast
majority of the grains were delivered to Earth as micrometeorites. In
this study, we extend the previous work, both in time and
geographically, by measuring concentrations and isotopic ratios of Ne in
individual SEC grains (60-120 μm in diameter) from three different
beds from a contemporary Middle Ordovician limestone section in China.
All of the Chinese SEC grains, 44 in total, contain surface-implanted Ne
of fractionated solar wind composition, implying that these grains were,
as in the case of the Swedish SEC grains, delivered to Earth as
micrometeorites. This gives further compelling evidence that the two to
three orders of magnitude increase in the influx of micrometeoritic
material following the breakup of the L-chondrite parent body was indeed
a global event. The rain of micrometeorites prevailed for at least 2 Myr
(the estimated time of the deposition of the topmost Chinese bed) after
the breakup event.