Cosmogenic nuclide enhancement via deposition from long-period comets - A test of the Younger Dryas impact hypothesis

Aug 27, 2026

Uploaded by Ophelia

The study investigates whether measurable excursions in 26Al can originate from direct deposition by extraterrestrial bolides, while atmospheric anomalies in 14C and 10Be may result from long-period comet impacts. It contrasts these pathways with standard cosmic-ray production in Earth’s atmosphere. The work computes expected 14C, 10Be, and 26Al contents on long-period comets as functions of comet mass and evaluates whether large comets entering Earth could generate recorded past signals. It further proposes using the 26Al/10Be ratio in ice cores as a definitive test for the Younger Dryas scenario.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages17

Reading Time43 min

AccessFree to download

Abstract

Introduction

Extraterrestrial impacts and atmospheric effects

Airbursts and evidence for Younger Dryas cooling

Long-period comets and cosmic-ray exposure

Deposition of cosmogenic residues

Cosmogenic nuclide enhancement via deposition from long-period comets as a test of the Younger Dryas impact hypothesis. Andrew C. Overholta,b, Adrian L. Melotta* 1 Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045 2 Department of Science and Mathematics, MidAmerica Nazarene University, Olathe, Kansas 66062 ABSTRACT We explore the idea that detectable excursions in 26Al may arise from direct deposition by any bolide, and excursions in 14C and 10Be abundances in the atmosphere may result from long-period comet impacts. This is very different from the usual processes of production by cosmic rays within Earth’s atmosphere. Long-period comets experience greatly increased cosmic ray flux beyond the protection of the sun’s magnetic field. We report the computed amount of 14C, 10Be, and 26Al present on long-period comets as a function of comet mass. We find that the amount of nuclide mass on large long-period comets entering the Earth’s atmosphere may be sufficient for creating anomalies in the records of 14Cand 10Be from past impacts. In particular, the estimated mass of the proposed Younger Dryas comet is consistent with its having deposited sufficient isotopes to account for recorded 14C and 10Be increases at that time. The 26Al/ 10Be ratio is much larger in extraterrestrial objects than in the atmosphere, and so, we note that measuring this ratio in ice cores is a suitable definitive test for the Younger Dryas impact hypothesis, even if the hypothetical bolide is not a long-period comet and/or did not contribute to the 14Cand 10Be increases. * Corresponding author Tel. 785-864-3037 Email addresses: [acoverholt@mnu.edu](acoverholt@mnu.edu), [melott@ku.edu](melott@ku.edu) 1. INTRODUCTION Impacts from extraterrestrial objects provide a significant threat over long timescales of damage and mass extinction for terrestrial biological systems. As well as directly damaging biological systems, extraterrestrial impacts are known to create long-lived atmospheric effects, such as ash and dust clouds. Little is known of the frequency of such events, and what is known depends greatly on cratering and other geologic data (Raup & Sepkoski 1984, Bland et al. 1998, Jetsu 2011) which do not measure airbursts. The extinction event at the end of the Cretaceous period (KPg boundary) coincides with a large bolide impact proposed to be the primary cause of the extinction event (Alvarez et al. 1980, Schulte et al. 2010) . Impact events are produced by a variety of extraterrestrial objects, including iron meteorites, rocky asteroids, and icy comets. Meteorites are well studied, because they typically leave craters and residual fragments of the initial object. In other cases, the impactor can break up in an airburst when rapid thermal expansion of the object produces fracturing and an apparent explosion of the nucleus before reaching ground level. These events are more difficult to study and leave less evidence than terrestrial impacts, making their frequency largely unknown. Major airbursts release a large amount of energy that may threaten biological systems, as an example, during the Tunguska event, which occurred above Siberia in 1908 (Farinella et al. 2001) . The mass of the Tunguska cosmic body is estimated to have been 5x107 kg (Wasson 2003) ; it produced the largest airburst in recorded history and felled an estimated 80 million trees. An event much larger than Tunguska has been suggested as the possible cause of the Younger Dryas cooling event of the late Pleistocene. Reported evidence for this impact includes peaks in microspherules, high-temperature melt-glass (>2100°C), iridium, osmium 1, polycyclic aromatic hydrocarbons, and nanodiamonds (Firestone et al. 2007, Kurbatov et al. 2010, IsradeAlcantaraz et al. 2012, Bunch et al. 2012, Mahaney et a. 2013), all of which are also present in the KPg boundary layer, and platinum, which is not (Petaev et al. 2013) . The impactor for this event was conje

FAQs

What hypothesis does the document test regarding the Younger Dryas event?

It tests whether long-period comet impacts could deposit cosmogenic nuclides that match observed 14C and 10Be increases, offering support for the Younger Dryas impact hypothesis.

How are 14C, 10Be, and 26Al treated in the proposed mechanism?

14C and 10Be anomalies are attributed to atmospheric deposition following long-period comet impacts, while 26Al excursions may arise from direct deposition by any bolide.

What definitive observational test does the paper suggest?

Measuring the 26Al/10Be ratio in ice cores, since extraterrestrial objects have a much larger ratio than the atmosphere.

Aug 27, 2026

Uploaded by Ophelia