Geology Reference
In-Depth Information
For the first few billion years the universe was filled only with stars that burnt hydro-
gen, but as some of the largest stars aged into red giants during the last 10% of their life-
times, heavier elements were formed in their immensely dense, hot centres. For much of
their life these stars burnt hydrogen, but then, as they died, pressures and temperatures
reached such high levels in their interiors that heavier elements were formed at an ever-
quickening pace. Carbon atoms were created when groups of three helium nuclei fused,
giving carbon nuclei with six protons and six neutrons, accompanied by vast releases of
energy. Then, as the stars aged even more, the denser elements such as sodium, mag-
nesium and oxygen were born as some of the carbon nuclei fused, until the sequence
reached iron, after which the creation of new elements stopped in all but the very largest
stars. Once the iron phase was reached inside these stellar giants, the pace of elemental
creation was frenetic, and in the last few seconds of their lives an inward gravitational
collapse generated sufficient energy to power massive supernova explosions which sent
vast quantities of hydrogen and smaller amounts of the heavier chemical beings such as
carbon, oxygen, phosphorus and sulphur whirling into the outer reaches of interstellar
space. Some of these clouds of atomic beings coalesced into new stars, giving rise to
fresh supernova explosions and more newly synthesised elements—a process that goes
on to this day. Thus many of the chemical beings which now constitute the Earth, and
indeed our whole solar system, have lived in several stars before coming to dwell in us
and in the rocks, atmosphere and ocean of our planet.
The Birth of Our Solar System
Sometimes a cloud of material flared forth by a supernova condenses into a nebular
cloud of dust, and this can in time differentiate out into a solar system. One such cloud,
in the outer reaches of a galaxy known as the Milky Way, became the solar system in
which Gaia resides. The cloud of interstellar matter that eventually became our Earth
had just the right combination of elements to give rise to a living planet. An astound-
ing 99% of the mass of the nebular cloud was hydrogen, with heavier elements weigh-
ing in at a mere 1%. However, amongst these relatively rare chemical beings there were
sufficient radioactive materials, such as radioactive potassium, uranium and thorium,
to provide a sufficient energy source in the inner earth to drive the movements of the
Earth's tectonic plates; there were also carbon, oxygen, hydrogen, sulphur and nitrogen,
which are essential for life, plus other elements such as iron, calcium magnesium and
oxygen, which formed the Earth's crust and its deep rocky interior.
