Geology Reference
In-Depth Information
The Future
Scenarios of a Changing Planet
Earth's Age: The next 5 billion years
Is the past prologue to the future? For Earth, the answer is yes, and no.
As in the past, Earth will continue to be a planet of incessant flip-flop patterns of change.
The climate will become warmer, then cooler, over and over again. Ice ages will return, as
willtimesoftropicalextremes.Platetectonics willpersist,shufflingcontinents,whileopen-
ing and closing oceans. Giant asteroid impacts and megavolcanoes will once again disrupt
life.
Butotherchangeswillbenew,andmanyofthemwillbeasirreversibleasthefirstgranite
crust. Myriad living species will die out, never to be seen again. Tigers, polar bears, hump-
back whales, pandas, gorillas—all are doomed. It's very possible that humans will die out,
too.
Many details of Earth's history are largely unknown, perhaps unknowable. But our plan-
et's rich history, coupled with natural laws, gives us a sense of what is to come. Let's start
with the long view and then focus closer and closer on modern times.
Endgame: Five Billion Years from Now
Earth is almost halfway to its inescapable demise. For 4.5 billion years, the Sun has shone
steadily, getting slightly brighter through time as it “burns” through its vast store of hydro-
gen fuel. For another five billion years (more or less) the Sun will continue to generate nuc-
lear energy by fusing hydrogen into helium. That's what most stars do most of the time.
Eventually the hydrogen will run out. Some smaller stars reaching this stage just peter
out, shrinking in size while sending out much less energy than before. Had the Sun been
such a “red dwarf” star, Earth's ultimate fate would be to freeze solid. Life, if it survived at
all, would be limited to a few hardy microbes deep underground, where liquid water could
persist.
The Sun won't die in that pitiful way, though, for it is massive enough to have a nuclear
backup plan. Remember that every star must balance two opposing forces. On the one hand,
gravitypullsthestar'smassinwardtomakeassmallasphereaspossible.Ontheotherhand,
nuclear reactions, like a continuous sequence of inner hydrogen bomb explosions, push out-
