Geoscience Reference
In-Depth Information
imply Earth-like conditions of climate and chemistry plus the existence of free oxygen,
something which, as far as we know, can only be maintained by life.
Signs of life
In February 1990, on its way out of the solar system after encounters with Jupiter and
Saturn, the Voyager I probe beamed back the first image of our entire solar system as it
might appear to visitors from another star. The picture is dominated by a single bright star,
our Sun, seen from 6 billion kilometres away, 40 times the distance from which we are used
to seeing it. The planets are scarcely visible. The Earth itself is smaller than one picture ele-
ment in Voyager's camera, its faint light caught in what looks like a sunbeam. This is our
whole world, seemingly just a speck of dust. But to any alien visitor with the right instru-
ments, that tiny blue world would immediately attract attention. Unlike the giant stormy
gas bags of the outer planets, cold, dry Mars, or the acid steam-bath of Venus, the Earth has
everything just right. Water exists in all three phases - liquid, ice, and steam. The atmo-
spheric composition is not that of a dead world that has reached equilibrium but one that
is active and must be constantly renewed. There is oxygen, ozone, and traces of hydrocar-
bons; things that would not exist together for long if they were not constantly renewed by
living processes. This alone would attract the attention of our alien visitors, even if they
could not detect the constant babble of our communications, radio and television.
Magnetic bubble
Geophysics goes way above our heads. I don't mean by that that it is incomprehensible but
that the physical influence of our planet extends far above its solid surface, way out into
what we regard as empty space. But it is not empty. We live in a series of bubbles nested
like Russian dolls one within another. The Earth's sphere of influence lies within the great-
er bubble dominated by our Sun. That in turn lies within overlapping bubbles blown by
the expanding debris of exploding stars or supernovae, long, long ago. They are all within
our Milky Way galaxy, which is in turn a member of a super-cluster of galaxies within the
known universe, which itself may be a bubble in a quantum foam of worlds.
The Earth's atmosphere and magnetic field shield us, for the most part, from the radiation
hazards from space. Without this protection, life on the Earth's surface would be threatened
by solar ultraviolet and X-rays as well as cosmic rays, high-energy particles from violent
events throughout the galaxy. There is also a permanent gale of particles, mostly hydrogen
nuclei or protons, blowing outwards from the Sun. This solar wind speeds past the Earth at
typical velocities of around 400 kilometres per second, and goes three times faster during a
solar storm. It extends for billions of kilometres out into space, beyond all the planets and
maybe beyond the orbits of comets, which reach out many thousands of times further from
