Geology Reference
In-Depth Information
a blazing fire transforms every bit of fuel to ash, all the energy has been used up. Iron is
the ultimate nuclear ash; no nuclear energy can be extracted by fusing iron with anything.
So when the first massive star produced its inevitable iron core, the game was over, the
results catastrophic. Until that point, the star had sustained a stable equilibrium, balancing
itstwogreatinnerforces:gravitypullingmasstowardthecenter,nuclearreactionspushing
mass outward from the center. When the core filled with iron, however, the outward push
just stopped, and gravity took over in an instant of unimaginable violence. The entire star
collapsed inward with such swiftness that it rebounded off itself and exploded in the first
supernova. The star was ripped apart, blasting most of its mass outward.
The Birth of Chemistry
For those readers who seek design in the cosmos, supernovas are nearly as good a place
to start as the Big Bang. To be sure, the Big Bang led inevitably to hydrogen atoms, and
hydrogen atoms just as inexorably produced the first stars. Yet it's not at all obvious how
stars, by themselves, get you to our modern living world. A big ball of hydrogen, even if it
does have a growing core-bound collection of heavier elements up to iron, doesn't seem to
help move things along in a very interesting way.
But when the first big stars exploded, cosmic novelty ensued. These fractured bodies
seeded space with the elements they had created. Carbon, oxygen, nitrogen, phosphorus,
andsulfur—theelements oflife—were especially abundant.Magnesium, silicon, iron,alu-
minum, and calcium, which dominate the compositions of many common rocks and form
a large fraction of the mass of Earth-like planets, also abounded. But in the incomprehens-
ibly energetic environment of these exploding stars, these elements fused in new and exot-
ic ways to make
all
the periodic table—elements way beyond number twenty-six. So ap-
peared the first traces of many rarer elements: precious silver and gold, utilitarian copper
and zinc, toxic arsenic and mercury, radioactive uranium and plutonium. What's more, all
these elements were hurled out into space, where they could find one another and clump
together in new and interesting ways through chemical reactions.
Chemistry happens when one everyday atom bumps into another. Every atom has a tiny
but massive central nucleus with a positive electric charge, surrounded by a cloudlike dis-
tribution of one or more negatively charged electrons. Isolated atomic nuclei almost never
interact, except in the ultimate pressure-cooker environments of stellar interiors. But elec-
tronsfromoneatomareconstantlybumpingintotheelectronsofadjacentatoms.Chemical
reactions occur when two or more atoms meet and their electrons interact and rearrange.
Such shuffling and sharing of electrons occurs because certain combinations of electrons,
notably collections of two or ten or eighteen electrons, are particularly stable.
