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It’s easy to understand how the price of a bar of chocolate might be correlated with weather patterns in Africa. Most cacao is grown in Africa, so if bad weather were to induce a change in the volume of the cacao harvest there, it would affect the global supply. Downstream, the price could change.
You might be more surprised to learn that the specific path the blazing sun cuts through the galaxy may have a direct influence on fluctuations in the diversity of microplankton in the Earth’s oceans. Such are the findings of a new preprint led by Peter Ozsvart at the Hungarian Academy of Sciences in Budapest. That’s because the flux of cosmic rays hitting the Earth varies, and this influences the rate of mutation in microplankton, Ozsvart and his colleagues found.
Microplankton are the foundation of the marine food web and support all higher marine life, such as fish and whales, so the findings suggest that tiny changes in the dynamics of our vast solar system may have had a profound impact on the evolution of life on Earth.
The sun is located about 26,000 light-years from the center of our galaxy, aka the Milky Way, and its orbit is close to circular, taking about 230 million years to complete one loop. As it orbits around the center of the galaxy, the sun oscillates vertically with an amplitude of about 200 light-years.
Tiny changes in the dynamics of our vast solar system may have had a profound impact on the evolution of life on Earth.
And these oscillations influence the flux of cosmic rays entering the solar system. Cosmic rays are energetic particles—mainly protons and other ions—accelerated to very high speeds, either by the sun itself or by more distant, galactic and extragalactic sources. When these cosmic rays collide with molecules in our atmosphere, they create cascades of other particles that shower onto the Earth and into its vast oceans. Such particle “showers” tend to lose their steam once they have traversed about 30 feet of water, which happens to be the domain of marine plankton.
Marine plankton are an enormous and diverse group of miniscule organisms that include phytoplankton, which belong to the plant kingdom, and zooplankton, which belong to the animal kingdom. Ozsvart and colleagues focused on four groups of microplankton whose evolutionary histories we already know a lot about, including how the number of species and genera have changed across geologic time.
The four groups of organisms—radiolarians, nannoplankton, dinoflagellates, and planktonic foraminifers—each have skeletons measuring between 2 and 300 microns, about the size of very finely ground coffee grains, and are found across a wide range of latitudes and water temperatures. Scientists have data about radiolarians extending back 500 million years, and for the other three stretching back 250 million years.
High-energy radiation damages genetic information, most often by breaking apart strands of DNA. Cells are designed to repair their own DNA, but the repair process is imperfect. This leads to mutations. The rate of mutations depends on the amount of repair needed, which is in turn affected by the cosmic ray flux.
Ozsvart and colleagues calculated the number of new genera of species for each of the groups throughout geologic time, and compared it against data about the cosmic ray flux on Earth. Their hypothesis was that the distribution of new microplankton genera should be higher at periods when the flux of cosmic rays was higher, and the data seemed to bear this out to a statistically significant degree.
Plankton are the largest source of oxygen in our atmospheres, and play key roles in cycling nutrients and maintaining the health of marine ecosystems. What would be the “downstream” consequences of an increase in microplankton biodiversity? Like the weather in Africa affecting the price of chocolate, it is possible—though difficult to predict—that such variations could spread from their local ecosystems throughout the oceans, and have a profound effect on the evolution of life as we know it.
Do seemingly distant, small variations in our cosmic environment play a central role in the evolution of life on Earth? Previous studies had proposed that galactic oscillations might correlate with mass extinction events, but such claims have been disproven. Still, the new findings suggest that when looking for striking forces and massive impacts that may have shaped evolution, it’s important to look beyond dinosaur-killing asteroids and mega-volcanoes to an even more powerful force in our galaxy: the sun. 
Lead image: Rich Carey / Shutterstock
