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.

They 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 does not stand still, in fact it orbits the centre
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 they 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”. They race through our solar system at a velocity of up
to 800 kilometres 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 colourful 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,
in other words, to be another source of energy which catapults the
particles into space. The hot favourites 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,” the US physicist adds.

Incidentally, 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.

Notes for editor:

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