Guest “Really?” by David Middleton
H/T to my friend Brian Pratt…Introduction
For starters, the author appears to totally fail to grasp the principle of uniformitarianism…
Since its introduction in 2007, the Younger Dryas impact hypothesis (YDIH) has received considerable attention, and sparked heated debate (Firestone et al., 2007). The occurrence of a global cosmic catastrophe, which the impact hypothesis suggests only slightly preceded the onset of human civilisation in the Fertile Crescent of south west Asia (as revealed by excavation of remarkable sites like Gobekli Tepe in this region), represents a paradigm-shift in understanding with profound consequences (Dietrich et al., 2012; Dietrich et al., 2017; Schmidt, 2012).
The debate surrounding catastrophism versus gradualism goes back at least as far as the great classical philosophers (Palmer, 2003). It was thought for many years to be resolved by Darwinian evolution and Hutton’s uniformitarian geological principles, at least within the general scientific community. But in recent decades, with the discovery of many large impact craters on terrestrial planets and moons, including Earth and our own moon, and with the discovery of over 1000 large (>1 km) asteroids in near-Earth space, the situation has reversed. Now, globally important cosmic impacts on Earth are expected on the timescale of millions of years (Harris and D’Abramo, 2015).Sweatman 2021
Uniformitarianism doesn’t exclude impacts/bolides, never has, never will.
After babbling on about black mats and naonodiamonds, the author then cited the Hiawatha crater in Greenland…
Following this, Kjaer et al. (2018) report the discovery of a large impact crater beneath Hiawatha Glacier in northwest Greenland. From airborne radar surveys, they identify a 31-km-wide, circular bedrock depression beneath up to a kilometre of ice. They further suggest the impactor was over 1 km wide and unlikely to predate the Pleistocene, i.e. it is less than a few million years old (see Fig. 11). This maximum age is confirmed a year later (Garde et al., 2020). Clearly, this crater is a candidate YD-age impact structure.Sweatman 2021
No… Hiawatha clearly isn’t “a candidate YD-age impact structure.”
From Garde et al., 2020…
One of these lumps yielded a non-finite 14C age of >43,500 yr B.P. (our sample Beta-471661). Most of the lignite consists of woody material.
Charcoal and abundant dispersed organic carbon in the impactite grains of glaciofluvial sand draining the Hiawatha crater come from local, thermally degraded conifer trees with a probable late Pliocene to early Pleistocene age of ca. 3–2.4 Ma.
In summary, the age of the organic carbon at Hiawatha is probably 3–2.4 Ma, and we favor the younger, 2.4 Ma age as the simplest interpretation and a realistic maximum age of the impact.Garde et al., 2020
The probable age (3 Ma to 2.4 Ma) is far older than the Younger Dryas (12.7 ka). If it occurred at Younger Dryas time, they would have been able to obtain finite 14C ages.
While the actual lines evidence for a significant Younger Dryas impact event are interesting, if not compelling, they’re almost all equivocal and most YDIH papers feature at least one “self-inflicted gunshot wound.”
Garde, Adam A., Anne Sofie Søndergaard, Carsten Guvad, Jette Dahl-Møller, Gernot Nehrke, Hamed Sanei, Christian Weikusat, Svend Funder, Kurt H. Kjær, Nicolaj Krog Larsen; Pleistocene organic matter modified by the Hiawatha impact, northwest Greenland. Geology 2020;; 48 (9): 867–871. doi: https://doi.org/10.1130/G47432.1
Sweatman, Martin B. The Younger Dryas impact hypothesis: Review of the impact evidence, Earth-Science Reviews, Volume 218, 2021, 103677, ISSN 0012-8252, https://doi.org/10.1016/j.earscirev.2021.103677.