The sun, while essential for life, can also be a source of destructive energy. Known as “solar particle events”, these blasts of protons from the sun’s surface can travel through space like a searchlight, potentially causing severe damage to Earth. Historical records indicate that an extreme solar particle event, capable of significantly depleting the ozone layer and increasing ultraviolet (UV) radiation, strikes Earth roughly every thousand years. These events, especially during periods of weakened Earth’s magnetic field, could have a dramatic impact on life on our planet.
Earth’s magnetic field acts as a protective shield, deflecting charged radiation from the sun. However, this field is not static and has undergone significant changes over time. In the past century, the north magnetic pole has been steadily drifting across northern Canada at a rate of approximately 40 kilometers per year, while the field itself has weakened. Geological records reveal that there have been periods when the geomagnetic field was either very weak or even nonexistent. The absence of a magnetic field is evident on Mars, which lost its global magnetic field in the ancient past, resulting in the loss of most of its atmosphere.
The sun’s outer atmosphere constantly emits a stream of electrons and protons known as the “solar wind.” But occasionally, the sun releases bursts of energy, predominantly protons, in solar particle events, often associated with solar flares. These protons, heavier than electrons, carry more energy, reaching lower altitudes in Earth’s atmosphere. While these interactions excite gas molecules, they emit X-rays, invisible to the human eye. Hundreds of weak solar particle events occur during each solar cycle (approximately 11 years), but scientists have discovered evidence of much stronger events throughout Earth’s history. Some of these extreme events were thousands of times more powerful than anything recorded by modern instruments. These extreme events occur on a timescale of centuries, with the most recent one happening around 993 AD. Their effects can be profound, as evidenced by Viking buildings in Canada constructed with materials showing signs of exposure to intense radiation.
Beyond their immediate impact, solar particle events can trigger a series of chemical reactions in the upper atmosphere that deplete ozone. Ozone plays a vital role in absorbing harmful UV radiation, which can damage eyesight, DNA (increasing the risk of skin cancer), and affect the climate. Using large computer models of global atmospheric chemistry, researchers have simulated the consequences of an extreme solar particle event. The findings indicate that such an event could deplete ozone levels for an extended period, leading to elevated UV levels at the surface and increased DNA damage. However, if a solar proton event occurs during a period of weak Earth’s magnetic field, the ozone damage could persist for several years, causing a substantial increase in UV levels and a significant boost in the rate of solar-induced DNA damage.
The combination of weak magnetic field and extreme solar proton events, while seemingly rare, is statistically likely to occur relatively often, potentially explaining several enigmatic events in Earth’s past. The most recent period of weak magnetic field, including a temporary reversal of poles, occurred approximately 42,000 years ago and lasted about 1,000 years. This period coincides with several major evolutionary events, such as the extinction of Neanderthals in Europe and the arrival of modern humans in the region. An even larger evolutionary event, the emergence of multicellular animals at the end of the Ediacaran period (565 million years ago), followed a prolonged period of weak Earth’s magnetic field. Similarly, the rapid diversification of animal life during the Cambrian explosion (539 million years ago) has also been linked to geomagnetism and heightened UV levels. The simultaneous evolution of eyes and hard body shells in various unrelated animal groups has been interpreted as a protective mechanism against the harmful incoming UV radiation, suggesting a “flight from light” strategy.
The relationship between solar activity, Earth’s magnetic field, and the history of life is still being explored. This research highlights the complex and potentially dangerous interactions between our planet and the sun, underscoring the importance of understanding these processes for the future of life on Earth.
