From Celestial Impact to Climatic Catastrophe

A Critical Examination of the Younger Dryas Comet Hypothesis

The Younger Dryas impact hypothesis posits that a series of comet impacts around 12,800 years ago initiated the Younger Dryas period, a sudden return to glacial conditions after the last Ice Age was seemingly concluding. In 2007, a year before I began my PhD at UCLA focusing on impacts, Richard Firestone and his colleagues proposed a groundbreaking hypothesis suggesting that a comet impact was responsible for the onset of the Younger Dryas period approximately 12,800 years ago. This theory was based on finding a layer rich in nanodiamonds, magnetic spherules, and other impact markers across multiple sites in North America. This layer, according to the hypothesis, was the fallout from a comet or asteroid impact that triggered massive environmental changes, leading to widespread extinctions and a sudden climate shift.

Sediment profiles for seven sites. Concentrations are shown for magnetic grains, microspherules, charcoal, soot, glass-like carbon, carbon spherules, Ir, Cr, and Ni, which peak mostly in a narrow stratigraphic section spanning only a few hundred years. Ir open circles indicate values below detection, typically <0.5–1 ppb. Ir uncertainties are ±10% at 117 ppb and ±90% at 2 ppb. Cr and Ni are less than ±20%. Keys are color-coded to match the respective curves, and graph points correspond to sampling locations on the photograph. The depth is in centimeters above or below the YDB. Source: https://www.pnas.org/doi/10.1073/pnas.0706977104

The introduction of this theory had a significant influence on the direction of my doctoral research, as it highlighted the potential for cosmic events to dramatically alter Earth's history. My work aimed to explore and critically evaluate the geological and chemical signatures associated with such proposed impact events, striving to understand their real implications on our planet's geological record, particularly on early Earth during the origin of life.

The impact theory is further outlined in Graham Hancock’s book "Magicians of the Gods” and appearances on The Joe Rogan Experience.