A shower of matter from space millions of years ago could have led to drastic changes in the Earth's climate, followed by the extinction of life on a massive scale -- which also killed off the dinosaurs. This at least is a theory put forward by scientists from the University of Bonn.
Normally, the solar wind acts as a shield against showers of cosmic particles, which prevents too many energy-rich particles from raining down on our atmosphere. Since 1997 scientists from Bonn, funded by the German Research Council (Deutsche Forschungsgemeinschaft, or DFG), have been examining how and why this gigantic shield works.
Dinosaurs were the undisputed masters of a whole geological era until they suddenly disappeared 65 million years ago. "Perhaps Earth just became too damp and too cold for dinosaurs at that time," Professor Hans Jörg Fahr from the Bonn Institute of Astrophysics and Extraterrestrial Research surmises.
The reason for the sudden change in climate could have been excessive pressure on our cosmic umbrella.
The solar system orbits the center of the Milky Way once every 250 million years. In the process, it also passes through dense clouds of interstellar matter, which causes problems for the solar wind and thus for the Earth.
Whereas the solar wind normally protects the Earth from a hail of interstellar particles like a huge bullet-proof vest, there are then suddenly up to a hundred times more particles raining down into the earth's atmosphere at enormous speeds.
On impact, the particles smash the air molecules into electrically charged fragments. These function as condensation nuclei on which droplets of water form.
“The result is dense cloud cover with greater precipitation and sinking temperatures,” says Professor Fahr, who bases his remarks on research worldwide.
Prof. Fahr and his colleagues, Dr. Horst Fichtner and Dr. Klaus Scherer, have shown that every 60 million years on average the solar system passes through dense clouds of matter, which could trigger off this sort of climate shock.
Prof. Fahr adds, "At roughly these intervals many species suddenly became extinct."
Research by other teams which have examined the link between cloud cover and solar activity has shown that cosmic factors could have had a dramatic impact on our climate on several occasions in the past.
"The less solar activity there is and therefore the less protection there is from the solar wind, the more cosmic particles reach the earth, and the more clouds form on earth," is how Prof. Fahr sums up the process.
Experts call the electrically charged particles which our sun emits "solar wind." These winds race through our solar system at a velocity of up to 800 kilometers per second, with a range extending a hundred times as far as the distance between the Earth and the sun.
"Every eleven years, the sun’s activity and therefore the solar wind reaches a maximum. At these times, for example, there is an increase in the frequency of the colorful auroras, when particles of the solar wind are captured by the Earth's magnetic field and are then catapulted into the upper atmosphere, where they make the oxygen glow," Dr. Michael Bird from the Institute of Radio Astronomy explains.
During particularly active phases, e.g., during big solar eruptions, the shower of particles can even interfere with short-wave reception, disrupt orbiting satellites or even "switch off" whole power stations.
"In Bonn we are especially interested in how the solar wind reaches its high velocities," Dr. Bird explains. "These cannot be explained solely by the enormous heat in the sun's atmosphere."
There seems to be another source of energy which catapults the particles into space. The hot favorites for Bonn's astrophysicists are exotic waves of magnetic fields in the corona, the "sun's atmosphere," which are amplified while they are expanding and then give the particles the necessary momentum.
"We are tracking these waves by using radio astronomy," Dr. Bird adds.
Cosmic weather might also be a decisive factor in the speed of evolution. The cosmic rays from which we are protected by the solar wind are so full of energy that they can change the DNA of living beings. If the solar wind's shield effect is too weak, i.e., the Earth's protective mantle is thin, within a short space of time this results in more mutations, which are the driving force of the evolution of life.
(Editor's Note: Images are available at this URL; unfortunately, the accompanying explanatory text is in German only.)
06-Jun-2002
