How safe is the Earth, really?

Charlie Stross has some surprising answers and ones that eco-fanatiocs should digest. Here are some extracts, but do read the whole of his article:

"imagine that, instead of being a perplexed mostly-hairless primate reading a blog, you're the guiding intelligence of an interstellar robot probe. You've been entrusted with the vital mission of determining whether a target planet is inhabitable by members of your creator species, who bear an eerie resemblance to H. Sapiens Sapiens. To gauge the suitability of the target world you've been given an incubator that can generate decorticated human clones — breathing meat-machines with nobody home up top. When you get to the destination you're going to transfer them to the surface and see how long they survive. If it can make it through 24 hours (or one diurnal period), congratulations! — you've found a potential colony world; one so hospitable that a naked and clueless human doesn't die on their first day out.

Your first destination planet is the cloud-whorled third planet out from an undistinguished G2 star, orbited by an airless, tidally-locked moon with roughly 1.3% of the planet's own mass. (Sound familiar? It should be.) You start sending down meat-machines to probe the surface at random. What conclusions do you draw about the inhabitability of Earth?

Let's start with Earth in its current configuration.

78% of the surface area is seawater. Drop a naked meat puppet there and it's going to go glug glug glub ... tritely, this is Not A Good Start.

Of the remaining 22%, about one third is either mountain ranges, deserts, or ice caps. It's reasonable to say that, in the absence of protective equipment, the meat probes are going to die of exposure in less than one diurnal period — possibly in as little as an hour if they're unlucky enough to land in the middle of the Antarctic winter.

We're down to about 15% of the planetary surface — 15% that isn't lethal without life support equipment such as boats, tents, and clothing. Our meat probes can breathe the air without their lungs freezing or dessicating. They aren't going to drown rapidly. And they aren't going to roll off a cliff. They might get a tad sunburned or hypothermic depending on the weather, and they might be eaten by a mountain lion or bitten by a rattlesnake, but they stand a reasonable chance of making it through 24 hours on the surface without dying.

Triumph! We have confirmed that a small part of this planet is inhabitable. Except ... I cheated. I pulled a fast one on you. Because I picked Earth in its current configuration — as it is today."

Interesting, isn't it?

It gets better (or worse):

"So here's the upshot: of the 4.6 Gy of Earth's known history, there's only been enough oxygen in the atmosphere for us to survive for about 0.5 Gy. For roughly 90% of the Earth's history we couldn't even breathe the air. And about 10-25% of the time, there have been ice ages so savagely fierce that the glaciers reached the tropics: odds are good that any meat probe landing on solid ground during these periods would rapidly die of exposure. So historically, Earth has only been inhabitable about 8% of the time — assuming you are lucky enough to find some solid ground. Once you factor in the random surface distribution, we're down to about 2% survivability."

I am sure you already know that a Gy is a gigayear and that 1Gy = 1,000,000,000 years.

Here's a final extract:

"So, back to the gedankenexperiment. Currently, a random meat probe dropped on the Earth's surface has something like a 15% chance of finding it survivable. But a random sampling over the historical epoch would return a survivability probability of around 1%. And over the future epoch, it's likely similar, unless we're erring massively on the side of pessimism about the prospects for our atmospheric composition remaining stable.

Ergo: to a space probe searching for somewhere that our kind of life can thrive, a truly random sampling of the Earth's surface (distributed over both time and area) would probably result in the conclusion that the planet is uninhabitable."

Well that's set me thinking, how about you?