Younger Dryas Impact Hypothesis - Criticism

Criticism

A study of Paleoindian demography found no evidence of a population decline among the Paleoindians at 12,900 ± 100 BP, which was inconsistent with predictions of an impact event. The suggested that the hypothesis would probably need to be revised. There is also no evidence of continent-wide wildfires at any time during terminal Pleistocene deglaciation, along with evidence that most larger wildfires had a human origin, which calls into question the origin of the "black mat." Iridium, magnetic minerals, microspherules, carbon, and nanodiamonds are all subject to differing interpretations as to their nature and origin, and may be explained in many cases by purely terrestrial or non-catastrophic factors.

Since it is assumed the effects of the putative impact on Earth's biota would have been brief, all extinctions caused by the impact should have occurred simultaneously. However, there is much evidence that the megafaunal extinctions that occurred across northern Eurasia, North America and South America at the end of the Pleistocene were not synchronous. The extinctions in South America appear to have occurred at least 400 years after the extinctions in North America. The extinction of woolly mammoths in Siberia also appears to have occurred later than in North America. A greater disparity in extinction timings is apparent in island megafaunal extinctions that lagged nearby continental extinctions by thousands of years; examples include the survival of woolly mammoths on Wrangel Island, Russia, until 3700 BP, and the survival of ground sloths in the Antilles, the Caribbean, until 4700 cal BP. The Australian megafaunal extinctions occurred approximately 30,000 years earlier than the hypothetical Younger Dryas event.

The megafaunal extinction pattern observed in North America poses a problem for the bolide impact scenario, since it raises the question why large mammals should be preferentially exterminated over small mammals or other vertebrates. Additionally, some extant megafaunal species such as bison and Brown bear seem to have been little affected by the extinction event, while the environmental devastation caused by a bolide impact would not be expected to discriminate. Also, it appears that there was collapse in North American megafaunal population from 14,800 to 13,700 BP, well before the date of the hypothetical extraterrestrial impact, possibly from anthropogenic activities, including hunting.

Scientists have asserted that the carbon spherules originated as fungal structures and/or insect fecal pellets, and that the claimed nanodiamonds are actually misidentified graphene and graphene/graphane oxide aggregates. An analysis of a similar Younger Dryas boundary layer in Belgium yielded carbon crystalline structures such as nanodiamonds, but the authors concluded that also did not show unique evidence for a bolide impact. Researchers have also have not found any extraterrestrial platinum group metals in the boundary layer which would be inconsistent with the hypothesized impact event. Further independent analysis of were unable to confirm prior claims of magnetic particles and microspherules, concluding that there was no evidence for a Younger Dryas impact event.

Other research has shown no support for the impact hypothesis. One group examined carbon-14 dates for charcoal particles that showed wildfires occurred well after the proposed impact date, and the glass-like carbon was produced by wildfires and no lonsdaleite was found.

Research published in 2012 has shown that the so-called "black mats" are easily explained by typical earth processes in wetland environments. The study of black mats, that are common in prehistorical wetland deposits which represent shallow marshlands, that were from 6000 to 40,000 years ago in the southwestern USA and Atacama Desert in Chile, showed elevated concentrations of iridium and magnetic sediments, magnetic spherules and titanomagnetite grains. It was suggested that because these markers are found within or at the base of black mats, irrespective of age or location, suggests that these markers arise from processes common to wetland systems, and probably not as a result of catastrophic bolide impacts.