A new study proposes that major biodiversity changes are linked to supernovae—the explosions of massive stars, suggesting that cosmic processes and astrophysical events influence the evolution of life on Earth.
A team of scientists at DTU Space (Denmark’s space research institute) say they have found a strong correlation between changes in the diversity of marine life in the past half a billion years and the occurrence of local supernova explosions.
According to Henrik Svensmark, one author of the study, it is possible that supernova bring about violent changes in Earth’s climate.
“A high number of supernovae leads to a cold climate with a large temperature difference between the equator and polar regions,” said Svensmark. “This results in stronger winds, ocean mixing, and transportation of life-essential nutrients to the surface waters along the continental shelves.”
The team’s paper states, “In accordance with the cosmic ray theory, Earth experienced cold glacial periods when the local supernova frequency was high … high cosmic rays and warm climates when the flux was low. These results suggest that changes in supernovae frequency and, thereby, changes in cosmic rays have significantly influenced the Phanerozoic climate.”
The paper goes on to suggest a correlation between past supernova rates and the burial of organic matter in ocean sediments during the last 500 million years. The sequence goes like this: supernovae rates influence climate; climate influences atmosphere–ocean circulation; that circulation brings nutrients to marine organisms; nutrient concentrations control bioproductivity (how organisms thrive); then, as they die, their remains settle into sea sediments, which fossilize and preserve the record of past biological activity.
All of this appears to correlate with changes in supernova rates — supernovae look to influence climate and the energy available to biological systems.
Variations in relative supernova history (black curve) compared with genera-level diversity curves normalized with the area of shallow marine margins (shallow areas along the coasts). The brown and light green curves are major marine animals’ genera-level diversity. The orange is marine invertebrate genera-level diversity. Finally, the dark green curve is all marine animals’ genera-level diversity.
Abbreviations for geological periods are Cm Cambrian, O Ordovician, S Silurian, D Devonian, C Carboniferous, P Permian, Tr Triassic, J Jurassic, K Cretaceous, Pg Palaeogene, Ng Neogene. [Henrik Svensmark, DTU Space]
Svensmark’s team studied the fossil record of ancient shallow marine areas. These were along the edges of oceans and other bodies of water in the Phanerozoic period of Earth’s geologic history–the period of time we’re in now–which began some 542 million years ago. On studying the rates of change in species of life they found clear evidence of explosions in biodiversity–which, to some degree, recalls the work of Robert Felix, namely ‘Magnetic Reversals and Evolutionary Leaps’ (worth a read).
Next, the team looked at the astrophysical fossil record of supernovae. They studied supernova frequencies recorded in three data sets of open stellar clusters. Those catalogs contain data about clusters within 850 parsecs of the Sun, with ages 520 million years and younger. The team then correlated the data with each other and linked higher-than-normal rates of past supernova explosions with climate-influenced changes in biodiversity in shallow marine environments here on Earth.
THE MECHANICS
The chain of events that leads from star death to biodiversity changes on Earth begins with a massive progenitor star reaching the end of its life and collapsing in on itself. The infalling material rebounds off the stellar core and rushes out into to space.
That cloud of debris scatters all the elements made by the star both before and during the supernova explosion. The event also emits vast amounts of cosmic rays. Those energetic particles eventually arrive in our Solar System. Some smash into Earth’s atmosphere and send showers of ions crashing through our protective layers. In line with the CR theory, these assist in the creation of aerosols that in turn form clouds (more cosmic rays = more clouds = global cooling).
Clouds regulate solar energy, controlling how much sunlight reaches Earth’s surface. The warmth of the sunlight is one part of the water-warmth-nutrient triad that enables life to form and thrive on the planet. The influence of supernovae is part of the cycle of substantial climate shifts, thanks to the intensity of cosmic rays.
According to Svensmark, those changes can be as much as several hundred percent over millions of years: “The new evidence points to a connection between life on Earth and supernovae, mediated by the effect of cosmic rays on clouds and climate”, he said.
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The Life of Earth
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