Frenzied star-making in the Milky Way Galaxy starting about 2400 million years ago had extraordinary effects on life on Earth. Harvests of bacteria in the sea soared and crashed in a succession of booms and busts, with an instability not seen before or since. According to new results published by Dr. Henrik Svensmark of the Danish National Space Center in the journal Astronomische Nachrichten, the variability in the productivity of life is closely linked to the cosmic rays, the atomic bullets that rain down on the Earth from exploded stars. They were most intense during a baby boom of stars, many of which blew up.
'The odds are 10,000 to 1 against this unexpected link between cosmic rays and the variable state of the biosphere being just a coincidence, and it offers a new perspective on the connection between the evolution of the Milky Way and the entire history of life over the last 4 billion years,' Dr Svensmark comments.
Dr Svensmark looked at the long record of life's bounty given by counts of heavy carbon atoms, carbon-13, in sedimentary rocks. When bacteria and algae in the ocean grow by taking in carbon dioxide, they prefer the ordinary carbon-12 atoms. As a result, the sea becomes enriched in carbon-13, which is acceptable to sea creatures building their carbonate shells. Variations in carbon-13 therefore record how much photosynthetic growth was in progress when the shell-makers were alive in other words, how productive the biosphere was at that time.
To his surprise, Dr Svensmark noticed that the biggest fluctuations in productivity coincided with high star formation rates and cool periods in Earth's climate. Conversely, during a billion years when star formation was slow, cosmic rays were less intense and Earth's climate was warmer, the biosphere was almost unchanging in its productivity.
This reveals a link more subtle than any straightforward idea of, say, a warm climate being life-friendly or a cold climate
Contact: Dr Henrik Svensmark
Danish National Space Center