The stellar baby boom period of the Milky Way sparked a flowering and crashing of life here on Earth, a new study suggests.
About 2.4 billion years ago, when the Milky Way started upping its star production, cosmic rays — high-speed atomic particles — started pouring onto our planet, causing instability in living organisms. Populations of bacteria and algae repeatedly soared and crashed in the oceans.
The researchers counted the amount of carbon-13 within sedimentary rocks, the most common rocks exposed on the Earth's surface. When algae and bacteria were growing in the oceans, they took in carbon-12, so the ocean had an abundance of carbon-13.
Many sea creatures use carbon-13 to make their shells. If there is a lot of carbon-13 stored in rocks, it means life, the origin of which is still unknown, was booming. Therefore, variations in carbon-13 are a good indicator of the productivity of life on Earth.
The researchers found that the biggest fluctuation in productivity coincided with star formation, which had an effect on Earth’s climate and therefore on the productivity of life on our planet.
According to one theory, when a star explodes far away in the Milky Way, cosmic rays penetrate through the Earth’s atmosphere and produce ions and free electrons. The released electrons act as catalysts and accelerate the formation of small clusters of sulfuric acid and water molecules, the building blocks of clouds. Therefore, cosmic rays increase cloud cover on Earth, reflecting sunlight and keeping the planet relatively cool.
Although cold and icy times are generally considered unfriendly to life, the data reveals that biological productivity kept oscillating between very high and very low. The reason, the researchers suggest, is that stronger winds during icy epochs stirred the oceans and improved the supply of nutrients in the surface waters.
“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,” said study author Henrik Svensmark of the Danish National Space Center.
The study was detailed in a recent issue of the journal Astronomische Nachrichten.