New Publication: A Global Environmental Crisis 42,000 Years Ago — the Adams Event

Today in Science, we report evidence that the last full reversal-like collapse of Earth’s magnetic field — the Laschamps excursion, around 42,000 years ago — coincided with a cascade of environmental and biological upheaval across the planet. We have named this short window the Adams Event, after Douglas Adams: the answer, of course, was always 42.

The headline result is that for roughly 800 years, Earth’s magnetic dipole weakened to less than 6% of its present strength, atmospheric ionising radiation surged, and a series of climatic, ecological and cultural shifts in the archaeological record line up against the same narrow window. The argument hinges on a beautifully preserved natural archive — sub-fossil New Zealand kauri trees (Agathis australis) — whose tree rings span the excursion and let us anchor the geomagnetic and radiocarbon records to calendar years with unusual precision.

Watch the explainer — narrated by Stephen Fry

The team put together an animated explainer for a general audience, narrated by Stephen Fry. It is, by some margin, the most enjoyable way to get the story:

If you only have 1 minute and 42s ;) for this paper, watch the video. If you have an afternoon, read on.

Why “Adams Event”

The Laschamps excursion has been known to geophysicists for decades, but its possible consequences for life on the surface have been hard to pin down because the radiocarbon timescale itself behaves strangely across it. Our reconstruction places the most dramatic phase — minimal field strength, peak cosmogenic-isotope production, and the proposed environmental crisis — at about 42,000 years ago. The number was too good to ignore. In the spirit of The Hitchhiker’s Guide to the Galaxy, we christened this short interval the Adams Event, an affectionate nod to Douglas Adams and the only sensible answer to life, the universe, and everything.

Key findings

Kauri tree rings pin down the excursion. Radiocarbon profiles from sub-fossil New Zealand kauri spanning ~41,000–42,500 years ago capture the rise and fall of atmospheric ¹⁴C driven by the collapsing geomagnetic shield, providing the first absolutely dated record of the Laschamps in a terrestrial archive.
A near-total magnetic collapse. Global geomagnetic modelling indicates dipole strength fell to <6% of modern values for several centuries around 42 ka, with the transition phases lasting roughly 800 years in total.
An atmospheric and climatic cascade. Increased solar and galactic cosmic radiation, ozone depletion, and shifts in atmospheric circulation are consistent with abrupt climate change recorded across the Pacific, Australasia and the Americas at this time.
Concordance with biological and cultural turnovers. The Adams Event aligns with the disappearance of Australian megafauna, the final decline of the Neanderthals in Europe, and a marked uptick in figurative cave art and the use of red ochre and cave-deep refugia — all behaviours consistent with populations responding to a more hostile sky.
A general framework, not a single-cause story. We do not argue the Laschamps “caused” every event of the period. Rather, a short, severe geomagnetic minimum is a plausible common forcing whose fingerprints appear across otherwise unconnected proxy records.

Significance

The Adams Event reframes the Laschamps from a curiosity of palaeomagnetism into a candidate trigger for one of the more turbulent intervals in recent Earth history. It also has a contemporary edge: Earth’s dipole has weakened by roughly 9% over the last 170 years, and the South Atlantic Anomaly is expanding. The deep past will not tell us when the next excursion will occur, but it offers a calibrated look at what an Earth with a much weaker magnetic shield can do to climate, ecosystems and the species living through it.

Data Availability

Kauri radiocarbon data, geomagnetic reconstructions, and modelling code are provided in the supplementary materials of the paper and through the data repositories listed therein.

📄 Read the paper | 🎬 Watch the Stephen Fry explainer

Citation: Cooper, A. et al. A global environmental crisis 42,000 years ago. Science 371, 811–818 (2021).

Journal: Science Volume 371, Issue 6531 Published: 19 February 2021 DOI: 10.1126/science.abb8677