How cosmic events may have influenced hominin evolution

This is an extract from Our Human Story, our newsletter about the revolution in archaeology. 
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I distinctly recall when the theory proposing that an asteroid impact led to the extinction of the dinosaurs first gained traction. The groundbreaking work by Luis Alvarez and his team, published in 1980 – just a year before my birth – asserted this dramatic idea without even identifying a crater, only the presence of a unique rock layer. It took several decades to solidify this theory, culminating in the identification of the Chicxulub crater in Mexico during the 1990s, which was crucial in dating the impact. Despite this, debates continue about whether this singular event was the primary catalyst for the mass extinction or if dinosaurs exhibited signs of decline prior to the impact.

However, our own evolutionary journey lacked such cataclysmic events. The Chicxulub impactor was exceptionally large and catastrophic.

Nonetheless, Earth remains vulnerable to various cosmic threats. One intriguing hypothesis suggests that a peculiar event involving Earth’s magnetic field occurred approximately 42,000 years ago, potentially triggering an ecological crisis and aiding the extinction of Neanderthals, thus allowing modern humans to flourish. Initially proposed in a 2021 study published in Science, this theory received media attention as my colleague Karina Shah reported back then.

Additionally, various cosmic events, including smaller meteorite impacts and radiation from supernovae, continually challenge life on Earth. Could these cosmic phenomena have potentially shaped the trajectory of human evolution?

Magnetic Flips

Let’s examine Earth’s magnetic field, a protective shield generated by the movement of molten metal in the core, creating vast electrical currents. This field extends far into space, safeguarding life from intense solar radiation and cosmic rays.

The magnetic field, however, is not static. Every few hundred millennia, it undergoes reversals, flipping its direction, thereby temporarily weakening and exposing Earth to increased radiation. Conversely, frequent excursions indicate significant shifts in the magnetic field’s strength and direction without complete reversals.

The Laschamps excursion occurred about 42,000 years ago, during which the magnetic field nearly reversed, lasting several centuries. A 2021 study suggested that during this period, changes in atmospheric ozone levels could have led to geological and ecological upheaval, impacting the archaeological record as well.

An April 2023 follow-up study modeled the Laschamps event and indicated that auroras might have been visible further south, affecting areas like Europe and northern Africa. Consequently, the increased exposure to harmful ultraviolet radiation could have impacted hominins during this period, leading to advancements in protective techniques, such as using ochre for skin protection and enhanced clothing craftsmanship.

This series of events raises intriguing questions about the fate of Neanderthals, whose extinction coincides suspiciously with this magnetic field excursion.

However, we should consider the broader context of human evolution over the last 7 million years. Magnetic field reversals have been frequent, and Neanderthals thrived through at least three prior excursions. If the Laschamps event were a critical factor in their extinction, we would expect increased extinction rates in other species as well, yet evidence suggests this wasn’t the case.

Exploding Stars

As we explore even more distant cosmic threats, such as supernovae, we uncover additional complexities. These massive stars, upon exploding, discharge immense quantities of matter and radiation, leading to significant effects on the solar system.

Recent research has suggested several supernovae occurred within the last 4 million years, with potential links to extinction events. In a 2023 study, scientists suggested that increased cosmic rays from a supernova may have precipitated climatic changes that adversely affected australopithecines at the time. However, the overwhelming consensus among paleontologists typically attributes extinction events to other ecological factors.

The takeaway from this cosmic narrative is clear: while numerous celestial phenomena have occurred throughout human evolutionary history, there’s scant evidence to suggest that they played decisive roles in the extinction of our species’ close relatives or that they were catalysts for major evolutionary adaptations.

The next time a headline claims cosmic events were responsible for significant evolutionary shifts or extinction events, it is wise to view such assertions with skepticism and consider the complex tapestry of factors that have shaped human history.