The vibrant auroras observed earlier this year have a darker side, revealing the destructive potential of solar storms. Occasionally, the sun emits powerful “solar particle events” (SPEs), which are bursts of protons that can significantly impact Earth.
Records show that every thousand years or so, Earth gets hit by an extreme SPE, which can severely damage the ozone layer and increase ultraviolet (UV) radiation levels on the surface. A recent study, published on July 1, analyzed the potential impacts of such extreme events, especially when Earth’s magnetic field is weak, suggesting dramatic effects on life across the planet.
Earth’s Magnetic Shield and Its Importance
Earth’s magnetic field acts as a protective shield, deflecting harmful solar radiation. This field, which has weakened by more than 6% in the past century, varies significantly over time. Periods of weak or absent geomagnetic fields have occurred throughout history, with geological records indicating significant changes.
The magnetic field’s protection is crucial, as evidenced by Mars, which lost its global magnetic field in the ancient past. As a result, Mars experienced a strong SPE in May that disrupted spacecraft operations and elevated surface radiation levels significantly.
The Power of Protons
The sun’s outer atmosphere constantly emits a fluctuating stream of electrons and protons known as the “solar wind.” However, the sun also sporadically emits bursts of energy, primarily protons, during SPEs, which are often associated with solar flares. Protons, being heavier than electrons, carry more energy and reach lower altitudes in Earth’s atmosphere, exciting gas molecules to emit X-rays, which are invisible to the naked eye.
Hundreds of weak SPEs occur every solar cycle (roughly 11 years), but historical records indicate that some extreme events were thousands of times stronger than anything recorded with modern instruments.
Extreme Solar Particle Events
Extreme SPEs occur roughly every few millennia, with the most recent event around 993 AD. Such events can deplete ozone levels for a year or more, increasing UV levels at the surface and causing DNA damage. If an SPE hits during a period of weak magnetic field, ozone damage could last six years, increasing UV levels by 25% and boosting solar-induced DNA damage by up to 50%.
Historical Impact and Future Risks
The combination of weak magnetic fields and extreme SPEs has likely occurred multiple times in Earth’s history, coinciding with major evolutionary events. For instance, the last period of weak magnetic field, starting 42,000 years ago, saw the disappearance of Neanderthals in Europe and extinctions of megafauna in Australia. Similarly, the origin of multicellular animals and the rapid evolution during the Cambrian Explosion have been linked to geomagnetic changes and high UV levels.
Exploring the role of solar activity and Earth’s magnetic field in the history of life is still in its early stages, but it’s clear that these factors have played significant roles in shaping our planet’s biological history.
