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I remember when the concept of an asteroid impact causing the extinction of the dinosaurs was a new and thrilling idea. Luis Alvarez and his team first put forth this theory in 1980—the year before I was born. It was a bold assertion, despite the absence of concrete impact crater evidence at the time, relying instead on an unusual rock formation. It wasn’t until the 1990s, with the identification of the Chicxulub impact crater, that the theory gained substantial traction in paleontological circles. To this day, scientists debate whether the impact was the primary driver of extinction or if dinosaurs were already in decline prior to the asteroid’s strike.

Clearly, nothing comparable occurred during the period of human evolution. The Chicxulub impact was notably catastrophic.

Yet, Earth faces numerous other cosmic hazards. A theory suggests that around 42,000 years ago, anomalies in the Earth’s magnetic field may have triggered a global ecological crisis, potentially contributing to the extinction of Neanderthals. This theory was initially proposed in 2021 in Science, and my colleague Karina Shah covered it in a news article.

Moreover, various cosmic events can affect our planet. Smaller meteorite impacts can severely disrupt ecosystems in their vicinity. Additionally, radiation from exploding stars and “supernovae” subject life on Earth to ongoing existential threats, including that of humans and their extinct relatives.

So, did cosmic events play a role in shaping human evolution?

Magnetic Field Fluctuations

Let us first examine the Earth’s magnetic field. Generated by the movement of molten metals within the Earth’s core, this magnetic field extends far into space, offering protection from harsh solar radiation and cosmic rays.

However, this magnetic field is not entirely stable. Every 100,000 years, it undergoes a flip where the north magnetic pole becomes the south pole. During these reversals, the field’s strength diminishes, allowing more radiation to penetrate the surface.

While these events aren’t catastrophic, there are also “excursions,” where the field strength wanes over extended periods, sometimes altering direction before returning to its original state without a full reversal.

The Laschamps event, occurring about 42,000 years ago, is a notable example where the magnetic field almost completely reversed. A 2021 study indicated this event lasted several hundred years, manifesting severe changes in atmospheric ozone levels. The researchers posited that these shifts likely incited “global climate change, resulting in environmental upheaval, extinction events, and alterations in archaeological records.”

Recent follow-up research has refined these ideas, suggesting that during the field’s excursion, phenomena such as auroras would have been visible farther south, affecting areas like Europe and North Africa and potentially exposing populations to harmful UV rays.

The authors further proposed that early modern humans in western Eurasia might have used a red pigment called ochre as a form of sunscreen, while also developing better clothing techniques. Such adaptations may have aided their survival against increased radiation exposure, unlike Neanderthals who lacked such adaptations.

Interestingly, the timing of the Laschamps event aligns closely with the last known presence of Neanderthals, raising questions about its possible role in their extinction.

Nevertheless, if we take a broader view of the past seven million years of human evolution, multiple magnetic field fluctuations have occurred. How did these excursions and reversals affect life during those times?

Historically, the last complete magnetic reversal occurred during the Brunhes-Matuyama transition around 795,000-773,000 years ago, long before Neanderthals but perhaps around the time of a common ancestor with us. Further explorations reveal numerous magnetic inversions throughout the past seven million years.

While smaller excursions are more frequent, securing evidence of them is challenging. A 2008 analysis identified 14 confirmed excursions over the past two million years, plus six others with weaker support.

Considering that Neanderthals experienced at least three excursions prior to the Laschamps event, why would this particular event lead to their extinction?

In fact, the Laschamps event posed significant hazards; if Neanderthals were vulnerable, it’s likely that other species suffered as well. Many megafauna species became extinct in Australia around 50,000 years ago, yet large animals in the Americas survived much longer, well into the 13,000-year mark. Notably, there was no significant spike in extinctions around 42,000 years ago.

This raises skepticism regarding the hypothesis linking the Laschamps event to Neanderthal extinction. While it may have contributed, it likely wasn’t the primary factor.

Similar issues plague claims about cosmic events impacting human evolution.

Impact Events

I’m fascinated by meteorite impacts. For an interesting afternoon rabbit hole, check out Impact Earth, an interactive map showcasing impact craters on our planet. For example, consider the Zhamanshin Hypervelocity Impact Crater in Kazakhstan, which is 13 km wide and is about 910,000 years old, or the Puntas Macrater in Nicaragua, which is 14 km wide and dates back 804,000 years. Both are notable compared to the Barringer Crater in Arizona, which measures just 1.2 km and is 61,000 years old.

Impact Earth catalogues 48 craters and sediments from the last 2.6 million years of geological history. If we expand our view back to the dawn of humanity, the number increases. Some noteworthy examples include:

• Schnack in Kazakhstan, 7-17 million years ago, 2.8 km wide
• Bigaha in Kazakhstan, possibly 6 million years ago, 8 km wide
• Karla in Russia, 4 to 6 million years ago, 12 km wide
• Zenker in Mongolia, 4.9 million years ago, 7 km in diameter
• Roller Kamm in Namibia, 3.8 million years ago, 2.5 km wide
• El’gygytgyn in Russia, 3.65 million years ago, approx. 15 km in diameter
• Aouelloul in Mauritania, 3.1 million years ago, 0.39 km wide

Keep in mind, none of these impacts come close to the scale of the Chicxulub crater. The largest craters are merely one-tenth the size. Nevertheless, such impacts can have significant localized effects.

Moreover, the timing and location of impacts matter. For instance, a significant event in Kazakhstan 6 million years ago likely did not affect humans, as they were confined to Africa at that time. However, what remained undisclosed was any research investigating the ecological repercussions of the Aouelloul and Roller Kamm impacts in Africa.

Another notable impact occurred around 790,000 years ago, resulting in unique tektites scattered across Southeast Asia and Australia. A 2019 study linked this to possibly the impact crater in Laos, measuring approximately 15 km in diameter. While it might have influenced Neanderthals, it was simply too distant and too early for it to be critical. However, it was undoubtedly significant for Homo erectus living in that region, but not impactful enough to change their survival as a species around 117,000 to 108,000 years ago.

The Exploding Stars

What about the more distant events, like exploding stars? When massive stars become supernovae, they release a massive outpouring of matter and radiation that traverses the galaxy. For years, we have known that nearby supernovae leave signatures in the rock record in the form of iron isotopes.

It’s challenging to pinpoint specific instances, but it appears a few supernovae events have occurred within the last 4 million years. Some research indicates event timelines such as 2.3 million years ago. I’ve also found other studies identifying incidents at 1.5-3.2 million years and 65-8.7 million years ago. Recently, researchers discovered evidence of supernova radiation hitting Earth around 2-3 million years ago.

This leads to speculation about potential impacts. One proposal suggests extra cosmic rays from a supernova might increase cloud cover, thus lowering temperatures, which could have influenced australopithecines living in Africa at that time. Perhaps.

Physicist Adrian Mellott of the University of Kansas has spent two decades delving into what he terms “astrobiophysics.” He investigates how cosmic events such as supernovae might influence life on Earth. Much of this research pertains to periods before the advent of Homo, but not all.

Mellott highlights a significant moment around 2.6 million years ago when the Pliocene epoch transitioned into the Pleistocene. During this time, large marine extinctions may have coincided with supernova activity. He posits that supernovae could have bombarded Earth with cosmic particles, potentially leading to climate change characterized by more frequent wildfires and increased cancer rates. However, many paleontologists who identified the extinction instead link it to diminishing productive coastal habitats.

The universe presents an extensive array of threats. It’s vital to understand that numerous potentially perilous cosmic events have transpired during human evolution. Yet, limited evidence supports the notion that any of these incidents led to the extinction of human ancestors or any other species.

Thus, I tend to believe that asteroid impacts, supernovae, and shifts in the Earth’s magnetic field played a minimal role in the grand story of human evolution. While some cosmic events may have had localized impacts, they aren’t equivalent to eradicating human species or catalyzing new adaptations.

Keep this perspective in mind the next time you read sensational headlines claiming cosmic events led to the demise of Neanderthals or other species.

Neanderthals, Ancient Humans, Cave Art: France

Join New Scientist’s Kate Douglas on an enthralling journey through time as she delves into the significant Neanderthal and Upper Paleolithic sites across southern France, from Bordeaux to Montpellier.