Geology Reference
In-Depth Information
Black Earth
The First Basalt Crust
Earth's Age: 50 to 100 million years
Earth has suffered more than a few transformative events in its long history. The Big
Thwack was surely the most disruptive and, in the consequent formation of the Moon, had
perhaps the most far-reaching effects. But such an outcome—a large solitary Moon orbiting
a planet full of volatiles—is by no means an inevitable outcome of the laws of chemistry
and physics. Had details of that ancient interaction between Earth and Theia unfolded with
only slight variations, the Moon-forming episode could have turned out very different. Had
the impact been better aimed, head-on and dead center, much more of Theia's mass would
havewoundupaspartofEarth.Inalllikelihood,wewouldnothaveasatellite,asTheiaand
Earth would have merged into one larger moonless world. Or had Theia just missed Earth,
its orbit might have been so altered as to be flung inward toward Venus or outward toward
Mars, perhaps to leave Earth's neighborhood forever. And had the impact been more glan-
cing, the distribution of scattered debris might have produced multiple, albeit much smaller,
moons to grace Earth's night sky.
Chance plays a significant role throughout our dynamic cosmic neighborhood. Our Solar
System's history is a litany of thwacks and near-misses. The asteroid that helped to kill off
the dinosaurs might just as well have been off the mark, saving
Tyrannosaurus
and its des-
cendants to evolve for tens of millions more years. Perhaps big-brained birds would have
become intelligent, flying toolmakers. Perhaps the runty mammals of that extended Meso-
zoic Era would have never amounted to much. With only a little tweak here or there, Earth
would have taken a different path.
But some aspects of the cosmos are inevitable, deterministic. The production of huge
numbers of protons and electrons, and of corresponding amounts of hydrogen and helium,
was hardwired into our universe from the instant of the Big Bang. The formation of stars
wasaninescapableconsequenceoftheproductionofhugeamountsofhydrogenandhelium.
The synthesis of all the other elements by nuclear fusion reactions and by supernovas was
equallypreordainedbytheformationofhydrogen-richstars.Andtheaccretionofallsortsof
interesting planets—Earth-like, Mars-like, Jupiter-like, and dozens more types that are only
now being discovered orbiting distant stars—followed with certainty from the synthesis of
all those chemical elements.
