Utrecht University

Graduate Student, Earth Sciences

Thesis Title: Were abrupt climate and environmental change at 12.9 ka initiated by an extraterrestrial impact?

About

For my PhD research I focus on an extraterrestrial impact at the Allerød – Younger Dryas boundary (~12,900 cal yrs BP) as proposed by Firestone et al. (2007). This impact or airburst allegedly resulted in abrupt climate cooling, large-scale wildfires megafaunal extinctions, and rapid human behavioral shifts. Evidence for this impact, coming from several sites in America and one in Belgium, originally consisted of peaks in: magnetic grains with iridium, magnetic micro-spherules, charcoal, soot, carbon spherules and glassy carbon containing nanodiamonds, and fullerenes with extraterrestrial helium. Not all of these are normally associated with impacts and although elevated iridium concentrations and hexagonal diamonds are associated with extraterrestrial impacts and meteorites, the evidence remains inconclusive, non-reproducible and/or heavily debated.

During my research I will concentrate on investigating three fractions of the Usselo Horizon in north-western Europe for possible evidence for an impact:

- The carbonaceous fraction. The carbon spherules and possibly the glass-like carbon are said to contain several forms of nanodiamond. One of those, hexagonal diamond, is thus far only known from meteorites or in relation to an extraterrestrial impact. The occurrence of charcoal yields information on the occurrence and temperature of wildfires. In addition, radiocarbon dating of charcoal particles can be used for further age control.
- The sand fraction. Shocked quartz is considered diagnostic evidence for an extraterrestrial impact. Thus far, no shocked quartz or other minerals have been reported at the Allerød – Younger Dryas boundary. However the absence of shocked quartz does not exclude the possibility of an impact, which can also occur over the ocean.
- The magnetic fraction. A peak in magnetic grains and spherules at the Younger Dryas boundary has originally been reported, but other research groups have thus far not been able to confirm these results and report the absence of any peak or (multiple) peaks at different levels. Although concentrations of spherules have been found in known impact layers, they are not considered diagnostic evidence as they can also form through different processes.

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