It’s all in the Statistics!

As is well known, Earth plays host to numerous meteors, some of which are big enough to reach the Earth’s surface as meteorites. What scares us, the human species as a whole, of course, are the ones large enough to cause significant damage—especially the ones that can cause mass extinctions.

Are the rates at which meteorites arrive at Earth cyclic? Can we predict when the next mass extinction (meaning almost certainly the end of the human race as we know it) will be upon us? It’s all in the statistics!

Of course, there’s no other way make predictions, other than to watch for patterns and extrapolate the timescales involved into the future. Based on past records, there are certain hypotheses about when and why some big rocks hurl towards the Earth—and the most interesting of them involves a phantom solar companion. Christened “Nemesis”, this hypothetical star is supposed to be lurking at the outer edges of the solar system, and like a classical villain hurling chunks of rock from the [Oort Cloud][linkoort] into the inner solar system. Essentially, he’s made out to be playing Duck Hunt, with Earth as the Duck, of course.

But all of this story (and other cyclical hypotheses) depends on a robust analysis of data, which involves robust statistical methods. Everything is a question of probability, of course—you can’t get absolute numbers in situations like these—and it’s no easy matter to set limits to what the error tolerances are. To understand how difficult the whole process is, consider the data in this case: cataloguing previous impact craters on Earth against how old they are. There are numerous craters, of course, but there are also erosion processes that make life difficult.

Well, according to this article by Ian O’Neill, there isn’t much statistical evidence after all for Mr. Nemesis. Researchers at the Max Plank Institute of Astronomy turned to Bayesian probabilities to look at the data, and concluded that there isn’t periodicity in the data as previously thought. Bayesian probabilities are a little more complex implementation of probability theory, where the question asked is: “What is the probability of event A, given that event B precedes it?” Event B, of course, has its own probability of occurring. (There are other complexities, of course, but that’s the simplest case.)

We’re not doomed by Nemesis after all! Apparently robust statistics has saved the day once again. :)

Or has it? The scientists did not find cyclical evidence that would point to Nemesis, but they think they’ve found evidence for an increasing rate of meteorites over the past 250 million years. And before you say “erosion!”–which would decrease the number of older craters—apparently the same trend is observed on the Moon, where there is, of course, no erosion going on.

So—we’re not out the woods yet! ;)

(In case you’re seriously wondering—no, there isn’t a serious chance that we’d be hit by a big one soon. There isn’t even a less serious chance. Doesn’t mean it’s impossible, though!)

Using Markdown by John Gruber

I’ve recently discovered Markdown by John Gruber, and it’s a nifty (and absolutely awesome) writing tool. If you prefer (like I do) doing the bulk of your writing in a text editor—rather than a word processor—Markdown is quite incredible.

And if you do all your writing in a word processor, try this out, seriously. Write everything up in a text file, without bothering about fonts or styles or page margins, and then import the document into your favorite word processor for styling. Personally, it’s less distracting, and more productive.

Just so you know—this post is written in Markdown, and then uploaded as HTML.

What Markdown is, is essentially a new ‘markup’ syntax (notice the irony in the name?). For example, HTML is a markup language—you do all your writing in a text file, and then you tag the text to give it different effect. HTML has different tags for linking, adding text effects, and a bunch of other things. Do you use (or have heard of) LaTeX? That’s another markup language: you do all your writing in a text file and then add tags to style the document.

The difference in case of Markdown is this: the tags it uses are all punctuation marks and symbols that we normally use anyway, for example in email. How would you show emphasis in a chat message? By using `*`, like this: `*emphasis*`. In Markdown you’d use the exact same syntax. It makes your text readable in addition to having all the markup included.

The only problem with writing all your text in a text file is, you have to go back into your word processor and actually add the styling—for example, the headings must be bold and a larger font, and you have to add the styling for subscripts and superscripts. With Markdown, all that is already done in the text file itself!

The natural export from Markdown is HTML (it’s tailored for web writing), but it’s elementary to import the HTML styled text into a word processor. And until you actually do that, you still have a text file that perfectly readable! (In addition, I think there are scripts available that do a direct conversion from Markdown text to MS-Word format. There’s also the [Dingus page][linkdingus] at Daring Fireball) to see your Markdown handiwork.

Excellent creation, John Gruber. I’ve been a fan of your tech-writing for a while now; now I also know why Markdown is so popular.