November 17, 2014
The air that we breathe
Last month, Google executive Alan Eustace made the highest sky dive ever, jumping from an altitude of 135,890 feet and breaking the sound barrier in the process. At 24 miles high, the sky above is black, the curve of the Earth is visible, and the near-vacuum and extreme temperatures requires a space suit.
And yet he was only a third of the way to the official edge of "space": 62 miles. It's another 40 miles to Low Earth Orbit (LEO). And then 100 miles on top of that to get to the ISS.
That may seem like a long way to go. It's not. The Earth's atmosphere is ridiculously thin. The diameter of the Earth is 8000 miles. A good pair of lungs will take you up another three miles. If a commercial jet aircraft--cruising at seven to eight miles--depressurizes, you'll need that emergency oxygen mask to stay alive.
If we generously define the atmosphere as ending at LEO and compare the planet to a baseball, the atmosphere would be thinner than a dime. Applying this analogy to breathable air only, the atmosphere is thinner than a sheet of paper.
Talk apples instead of baseballs, and the Earth's atmosphere is the mere skin of the fruit. This strikes me as a bad design flaw in the inhabitable planet design spec, though if the atmosphere reached any higher, nothing in LEO would stay in orbit for long.
This "skin of life" reinforces what a strange creature gravity is, simultaneously the strongest force in the universe--that can crush a star into a black hole--and the weakest. The paradox is so profound that physicists seriously theorize that gravity leaking into alternate universes saps its actual strength.
But gravity alone isn't enough to keep an atmosphere down on the farm. A small, rocky planet requires a molten core to power plate tectonics and a magnetic field.
The magnetic field forms radiation belts that deflect the solar wind around the atmosphere (the solar wind collides with the atmosphere at the poles and creates auroras).
The Saturnian moon of Titan is shielded by the magnetosphere of its mother planet. Locked in a close orbit to Saturn, tidal forces heat Titan's icy interior, creating an atmosphere denser at its surface than Earth's.
Titan's atmosphere is 98 percent nitrogen, its lakes liquid methane (-179 degree centigrade). But Titan could become beach-front property when the Sun enters its red giant phase five billion years from now and cooks the Earth to a cinder.
Though a gamma-ray burst could do us in long before then. Or a really big asteroid. Closer to home, there's always the Yellowstone Caldera.
It's a miracle we wake up every morning still breathing. The improbabilities of dying are balanced out by the improbabilities of existing in the first place. Like Dr. Who's Clara Oswald, Earth is, for the time being, the "impossible girl."
For all we know, the gods could get restless tomorrow and knock over our beautiful house of cards and play pinochle on our snouts. Which brings to mind the last scene from Cabin in the Woods:
Dana: I'm so sorry I almost shot you. I probably wouldn't have.
Marty: Hey, shh, no. I totally get it. I'm sorry I let you get attacked by a werewolf and then ended the world. [incredulous] Giant evil gods.
Dana: I wish I could have seen them.
Marty: I know. That would have been a fun weekend.
I'm with Marty. The only regret I have about the world ending one day is that I (probably) won't be there to see it. Throughout Buffy and Angel, Joss Whedon kept trying to end the world as we know it (an underlying flaw in both series). In Cabin in the Woods, the monsters take over and the world ends for good. Finally!
But to conclude on a more tuneful note: