3:30 PM - 3:45 PM
[BCG06-19] Investigation of a trigger for the mid-Ordovician ice age using helium isotopes: Evidence of an increased influx of extraterrestrial material
Keywords:Ordovician, ice age, extraterrestrial material, helium isotope, L-type chondrite
A large-scale glaciation event, known as the Hirnantian Ice Age, occurred at the end of the Ordovician period, and it is hypothesized that this cooling event triggered a mass extinction. Schmitz et al. (2019) suggested that a giant meteorite explosion and the subsequent influx of meteorite showers and cosmic dust may have initiated this cooling event, based on the abundance of L-chondrite meteorites in mid-Ordovician strata. Impact craters from this period have been identified globally, indicating a major collision in the asteroid belt that led to increased meteorite and cosmic dust influx to Earth (e.g., Tomkins et al., 2024). In Sweden, mid-Ordovician layers show both extraterrestrial L-chondrite fragments and a sharp rise in helium-3 (3He) concentrations, a marker of extraterrestrial material rarely found in terrestrial rocks.
In this study, we analyzed helium isotope ratios in layers with nearly the same age as the Swedish strata from Hubei Province, southern China. The samples were collected from the Puxi River section (Zhang et al., 2024), where chromium spinel derived from L-chondrites has been found. After being finely crushed and washed, the samples were wrapped in aluminum foil, introduced into a furnace, and heated to 1400°C under vacuum to extract helium for isotopic analysis. The results revealed a sharp increase in 3He concentrations around 470 million years ago, similar to the pattern observed in the Swedish strata. Although the 3He concentrations were lower than those in Sweden, the timing and pattern were remarkably similar. These findings suggest that both stratigraphic sections, despite being geographically distant, recorded the same event, indicating a large-scale, long-term influx of extraterrestrial material on a global scale around 470 million years ago.
Reference: Schmitz et al. (2019), Science Advances, 5, eaax4184; Tomkins et al. (2024), EPSL, 646, 118991; Zhang et al. (2024), EPSL, 643, 118891
In this study, we analyzed helium isotope ratios in layers with nearly the same age as the Swedish strata from Hubei Province, southern China. The samples were collected from the Puxi River section (Zhang et al., 2024), where chromium spinel derived from L-chondrites has been found. After being finely crushed and washed, the samples were wrapped in aluminum foil, introduced into a furnace, and heated to 1400°C under vacuum to extract helium for isotopic analysis. The results revealed a sharp increase in 3He concentrations around 470 million years ago, similar to the pattern observed in the Swedish strata. Although the 3He concentrations were lower than those in Sweden, the timing and pattern were remarkably similar. These findings suggest that both stratigraphic sections, despite being geographically distant, recorded the same event, indicating a large-scale, long-term influx of extraterrestrial material on a global scale around 470 million years ago.
Reference: Schmitz et al. (2019), Science Advances, 5, eaax4184; Tomkins et al. (2024), EPSL, 646, 118991; Zhang et al. (2024), EPSL, 643, 118891