Did exploding stars help life on Earth to thrive?

A new analysis of supernovae and geology by Dr. Henrik Svensmark of the Technical University of Denmark, posits that astronomical phenomena had a great influence upon life on Earth. Dr. Svensmark looked back through 500 million years of geological and astronomical data and considered the proximity of the Sun to supernovae as it moves around our Galaxy, the Milky Way. The announcement of the study from the Royal Astronomical Society reads:

Research by a Danish physicist suggests that the explosion of massive stars – supernovae – near the Solar System has strongly influenced the development of life. Prof. Henrik Svensmark of the Technical University of Denmark (DTU) sets out his novel work in a paper in the journal Monthly Notices of the Royal Astronomical Society.

When the most massive stars exhaust their available fuel and reach the end of their lives, they explode as supernovae, tremendously powerful explosions that are briefly brighter than an entire galaxy of normal stars. The remnants of these dramatic events also release vast numbers of high-energy charged particles known as galactic cosmic rays (GCR). If a supernova is close enough to the Solar System, the enhanced GCR levels can have a direct impact on the atmosphere of the Earth.

Prof. Svensmark looked back through 500 million years of geological and astronomical data and considered the proximity of the Sun to supernovae as it moves around our Galaxy, the Milky Way. In particular, when the Sun is passing through the spiral arms of the Milky Way, it encounters newly forming clusters of stars. These so-called open clusters, which disperse over time, have a range of ages and sizes and will have started with a small proportion of stars massive enough to explode as supernovae. From the data on open clusters, Prof. Svensmark was able to deduce how the rate at which supernovae exploded near the Solar System varied over time.

Comparing this with the geological record, he found that the changing frequency of nearby supernovae seems to have strongly shaped the conditions for life on Earth. Whenever the Sun and its planets have visited regions of enhanced star formation in the Milky Way Galaxy, where exploding stars are most common, life has prospered. Prof. Svensmark remarks in the paper, “The biosphere seems to contain a reflection of the sky, in that the evolution of life mirrors the evolution of the Galaxy.”

In the new work, the diversity of life over the last 500 million years seems remarkably well explained by tectonics affecting the sea-level together with variations in the supernova rate, and virtually nothing else. To obtain this result on the variety of life, or biodiversity, he followed the changing fortunes of the best-recorded fossils. These are from invertebrate animals in the sea, such as shrimps and octopuses, or the extinct trilobites and ammonites.

They tended to be richest in their variety when continents were drifting apart and sea levels were high and less varied when the land masses gathered 250 million years ago into the supercontinent called Pangaea and the sea-level was lower. But this geophysical effect was not the whole story. When it is removed from the record of biodiversity, what remains corresponds closely to the changing rate of nearby stellar explosions, with the variety of life being greatest when supernovae are plentiful. A likely reason, according to Prof. Svensmark, is that the cold climate associated with high supernova rates brings a greater variety of habitats between polar and equatorial regions, while the associated stresses of life prevent the ecosystems becoming too set in their ways.

He also notices that most geological periods seem to begin and end with either an upturn or a downturn in the supernova rate. The changes in typical species that define a period, in the transition from one to the next, could then be the result of a major change in the astrophysical environment.

Life’s prosperity, or global bioproductivity, can be tracked by the amount of carbon dioxide in the air at various times in the past as set out in the geological record. When supernova rates were high, carbon dioxide was scarce, suggesting that flourishing microbial and plant life in the oceans consumed it greedily to grow. Support for this idea comes from the fact that microbes and plants dislike carbon dioxide molecules that contain a heavy form of carbon atom, carbon-13. As a result, the ocean water is left enriched by carbon-13. The geological evidence shows high carbon-13 when supernovae were commonest – again pointing to high productivity. As to why this should be, Prof. Svensmark notes that growth is limited by available nutrients, especially phosphorus and nitrogen, and that cold conditions favour the recycling of the nutrients by vigorously mixing the oceans.

Although the new analysis suggests, perhaps surprisingly, that supernovae are on the whole good for life, high supernova rates can bring the cold and changeable climate of prolonged glacial episodes. And they can have nasty shocks in store. Geoscientists have long been puzzled by many relatively brief falls in sea-level by 25 metres or more that show up in seismic soundings as eroded beaches. Prof. Svensmark finds that they are what can be expected when chilling due to very close supernovae causes short-lived glacial episodes. With frozen water temporarily bottled up on land, the sea-level drops.

The data also support the idea of a long-term link between cosmic rays and climate, with these climatic changes underlying the biological effects. And compared with the temperature variations seen on short timescales as a consequence of the Sun’s influence on the influx of cosmic rays, the heating and cooling of the Earth due to cosmic rays varying with the prevailing supernova rate have been far larger.

The director of DTU Space, Prof. Eigil Friis-Christensen, comments: “When this enquiry into effects of cosmic rays from supernova remnants began 16 years ago, we never imagined that it would lead us so deep into time, or into so many aspects of the Earth’s history. The connection to evolution is a culmination of this work.”

See full paper here. This is a 20-page paper with many figures, 4Mb.

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5 comments

  1. This is an important scientific paper. Thanks for bringing it to my attention. No other reporting of this paper in the U.S. (checking Google News). It is another conformation of the impact of cosmic rays on climate. The global warmists have a lot of catching up to do. 

  2. Note to renewableguy: I have deleted your comment on GCR because it is irrelevant and misleading, and shows that neither you nor the propagandists at skeptical science have read the paper.  Had you read the paper you would see the explanation.

    1. Jon
      I doubt very much there is a connection between life thriving on earth and galactic cosmic rays. Misleading is actually wrong and it shouldn’t be your opinion alone to determine that. I presented an article based on several data sources explaining their point on GCR’s.

      Proganda would be based on countering the truth with possibly false information. You are showing yourself to be using strong arm tactics unnecessarily. If you are interested in a fair presentation of both sides then put my article back up. If you only want to  present one side, then by all means keep my post off.

      Skeptical science bases their postings on the current science.And yet you base your articles on the latest denial of AGW in the right wing circulation of entirely wrong and false media hype. 

      http://tucsoncitizen.com/wryheat/2012/03/27/rare-mineral-records-antarctica-temperature-history/

      The scientist refuted this false information very quickly. Your conclusion of medieval warming period was refuted by the very scientist that wrote it. This a true account of what has happened. Unless you would like to use your editorial power to rewrite that history.

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