Meanwhile, the sword
began to wilt into gory icicles,
to slather and thaw. It was a wonderful thing,
the way it all melted as ice melts
when the Father eases the fetters off the frost
and unravels the water-ropes. He who wields power
over time and tide: He is the true Lord.
— Beowulf, lines 1606 – 1611, in Seamus Heaney’s translation.
The hypothesis that a series of cosmic impact events was responsible for the Younger Dryas has stood up to a large statistical test, using Bayesian analysis.
The Younger Dryas period is particularly important in the story of our ancestry. (For instance, the decline of the Clovis culture has been attributed to it.) It was a burst of cold, arriving quickly, and not lasting for very long (geologically speaking). But it was long enough that, for living creatures, the resulting climactic shift could (and did) spell death for entire species, including mammoth and giant bears.
The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835– 12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼ 100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer.
A cosmic impact event at∼ 12,800 Cal B.P. formed the Younger Dryas boundary (YDB) layer, containing peak abundances in multiple, high-temperature, impact-related proxies, including spherules, melt glass, and nanodia monds. Bayesian statistical analyses of 354 dates from 23 sedimentary sequences over four continents established a modeled YDB age range of 12,835 Cal B.P. to 12,735 Cal B.P., supporting synchroneity of the YDB layer at high probability (95%). This range overlaps that of a platinum peak recorded in the Greenland Ice Sheet and of the onset of the Younger Dryas climate episode in six key records, suggesting a causal connection between the impact event and the Younger Dryas. Due to its rarity and distinctive characteristics, the YDB layer is proposed as a widespread correlation datum.
Notes & Quotes
They have 5 conclusions:
- “Bayesian analyses of 354 dates at 23 sites in 12 countries across four continents demonstrate that modeled YDB ages are consistent with the previously published range of 12,950–12,650 Cal B.P. (9, 11– 13), contradicting claims that previous YDB age models are inaccurate.”
“Bayesian analyses indicate that YDB dates could be synchronous within the limits of uncertainties (∼ 100 y), contradicting claims that YDB dates are diachronous.”
“Comparison with calibrated, unmodeled ages shows that Bayesian modeling does not significantly alter the calculated span of the YDB event.”
“The ages of the 23 sites are coeval with the Younger Dryas onset in six records and with the age of deposition of extraterrestrial platinum in the GISP2 ice core at the Younger Dryas onset. This temporal relationship supports a causal connection between the impact event and the Younger Dryas.”
“These analyses produced a more refined modeled age for the YDB event of 12,835– 12,735 Cal B.P. at 95% CI.”
Although Bayesian analysis alone cannot determine unequivocally that the YDB is synchronous at these 23 sites, a single event is the most plausible conclusion…
Now go lift something heavy,
PS. Photo Credit: ice age fauna of northern Spain.