Geology Reference
In-Depth Information
ThefirstchemicalreactionsfollowingtheBigBangproducedmolecules—smallclusters
of a few atoms tightly bound into a single unit. Even before hydrogen atoms began fusing
together in stars to form helium, hydrogen molecules (H
2
), each with two hydrogen atoms
chemicallybondedtogether,formedinthevacuumofdeepspace.Eachhydrogenatomcar-
riesonlyoneelectron,whichisaratherunstablesituationinauniversewheretwoelectrons
is a magic number. So when two hydrogen atoms meet, they pool their resources to form a
molecule with that magic number of two shared electrons. Given the abundance of hydro-
gen following the Big Bang, hydrogen molecules surely predated the first stars and have
been a perpetual feature of our cosmos since atoms first appeared.
Following the first supernova, as a variety of other elements seeded space, lots of other
interesting molecules could form. Water (H
2
O), with two hydrogen atoms bonded to an
oxygen atom, was one early example. Chances are that nitrogen (N
2
), ammonia (NH
3
),
methane(CH
4
),carbonmonoxide(CO),andcarbondioxide(CO
2
)moleculesalsoenriched
the space around supernovas. All of these molecular species would come to play key roles
in the formation of planets and in the origins of life.
Thencametheminerals—microscopicsolidvolumesofchemicalperfectionandcrystal-
line order. The first minerals could have formed only where the densities of mineral-form-
ing elements were high enough, but temperatures cool enough, for atoms to arrange them-
selves in little crystals. Just a few million years after the Big Bang, the expanding, cool-
ing envelopes of the first exploding stars provided the perfect settings for such reactions.
Tiny crystallites of pure carbon—diamond and graphite—were probably the first minerals
in the universe. Those pioneering crystals were like a fine dust, the individual grains indis-
cernibly small but perhaps large enough to add a bit of diamond sparkle to space. These
crystalline formsofcarbonweresoonjoinedbyotherhigh-temperature solidsthatfeatured
the more common elements, including magnesium, calcium, silicon, nitrogen, and oxygen.
Some were familiar minerals like corundum, the chemical compound of aluminum and
oxygen that is so valued in its richly colored varieties, ruby and sapphire. Tiny amounts
of the magnesium silicate olivine, the semiprecious birthstone of August, also appeared,
joined by moissanite, a silicon carbide often sold these days as a cheap synthetic substitute
for diamond. Altogether the interplanetary dust hosted perhaps a dozen common “ur-min-
erals.” Andso,with the explosion ofthe first stars, the universe began to get more interest-
ing.
Nothing happens only once in our universe (except perhaps for the Big Bang). Scattered
debris of old exploded stars were constantly subjected to the organizing force of gravity.
Thusremnantsoftheformerstellargenerationsinexorablyseedednewpopulationsofstars
by forming new nebulas, each a vast interstellar cloud of gas and dust representing the
wreckage of many prior stars. Each new nebula was more iron rich, and a little poorer in
hydrogen, than the one before. For 13.7 billion years, this cycle has continued, as old stars
