Holy Hit!

If you’ve seen the movies Deep Impact, Armageddon, Asteroid or The Land Before Time, chances are you’ve entertained the idea: what would I do if a meteor was on a collision course with Earth? What would happen? Would NASA send out a space shuttle to intercept the galactic gate-crasher? Could Iran be coaxed into donating its alleged caches of nuclear warheads to the task of obliterating the Earth-bound asteroid? What’s the post-apocalyptic weather like? Will you need to pack an extra jersey?

All of these are important questions. But not all meteorite strikes need to result in global catastrophe, although the dinosaurs would beg to differ. Some are actually responsible for sculpting some of the most beautiful landscapes and fascinating geological features here on our planet and on every planet.

Meteors, Meteorites, Meteoroids, Asteroids, Comets, Shooting Stars… What’s the Difference?

There are more names for space-travelling rocks than Elizabeth Taylor had surnames. But there is a degree of difference between them that needs to be appreciated, whereas I’m sure that each of Ms Taylor’s successive marriages was just as dull as the last.

A Comet is (relative to a planet) a small chunk of dirty ice-clad rock that orbits the Sun: think Halley’s Comet or Comet McNaught. When it comes close enough to the sun, blasts of solar radiation send particles of ice streaming off its surface to form a long visible train called a ‘coma’.

Comet McNaught blazes a beautiful trail across a star-studded sky. The Milky Way is actually one of the spiral arms of our galaxy. You’re welcome.

An Asteroid is a small chunk of rock that is also in orbit around the sun. Only, asteroids are composed of rock, metal and sometimes even organic compounds. Not ice. As a result, they don’t get to wear a bridal train.

A Meteoroid is, relative to an asteroid, a much smaller chunk of rock. Where asteroids can be kilometres in diameter, meteoroids are no more than 10 meters across, although they can also be as a small as a pebble. Anything larger officially joins the terminological ranks of asteroids.

A Meteor is a meteoroid that has made it into Earth’s atmosphere and is visible to us humans. Remember that one sexy night you spent with that guy in his crappy car, staring up at the stars? Suddenly, there was a brilliant streak of light across the night sky, and then he looked deep into your eyes and said that it was a sign you’d be together forever. And then he dumped you the week after for some tart with bigger knockers.

Yes! A shooting star and a meteor are one and the same thing.

Quick, make a wish!

A Meteorite – this is where things start getting interesting – is also a meteoroid (c’mon keep up!) But a meteorite survives its entry into the Earth’s atmosphere and actually makes it all the way to the ground where it causes all sorts of inconveniences for the local biology.

Now, we know that our local biology has been inconvenienced on several occasions by rocks galavanting around the galaxy. But how come our moon is more pock-marked than a pubescent teen and we seem to be relatively unscathed? Where are the big impact craters on Earth?

Turns out, everywhere.

Earth’s Impact Craters

Barringer Crater, Arizona, USA. Formed 50,000 years ago.

The largest confirmed impact crater on Earth is right here in my own back yard in a small town called Vredefort, South Africa. This appreciable dent in our planet’s facade (a 300 kilometre-wide dent to be precise) was caused by a meteor impact that happened over two billion years ago. This impact crater, which is now a UNESCO World Heritage Site, is even bigger than the crater left by the dinosaur-demolishing Chicxulub asteroid.

Take that Mexico.

Arial view of the Vredefort impact crater, Free State, South Africa. Formed more than 2 billion years ago.

According to the Earth Impact Database, there are 21 confirmed impact craters in Africa, 3 in Antarctica, 18 in Asia, 26 in Australia, 37 in Europe, 8 in South America and 30 in North America (31 if you count Chicxulub off the Yucatán peninsula, but last I heard the U.S. wasn’t very welcoming of Mexicans.)

These are confirmed impact craters, which have met the rigorous qualification requirements laid out by the Earth Impact Database; our official scientific pageant for meteor-strikes (world peace is most certainly not one of them). If we were to consider the list of unconfirmed impact craters, these numbers would easily double.

So you see, unscathed we are not. Our planet is just as pock-marked as the moon. We just have the benefit of plate tectonics, wind erosion, water erosion and a biosphere to cover up evidence of our acne scarring.

Gosses Bluff, Northern Territory, Australia. Formed 142 million years ago.

Somewhere off the Yucatán Peninsula in a Galaxy Surprisingly Nearby

65 million years ago, a large extraterrestrial hunk of rock approximately ten kilometres (6.2 miles) in diameter raged into Earth’s atmosphere and smashed into the ocean off the Mexican coast. Sunbathing dinosauritas didn’t even have a chance to reattach their bikini tops before a shockwave so f&*king inconceivable in size and rage hit, I am forced by sheer necessity to use a curse word as an adjective to describe it.

“Within microseconds, an unimaginable explosion released as much energy as billions of Hiroshima bombs detonated simultaneously, creating a titanic fireball hotter than the Sun that vaporized the ocean and excavated a crater 180 kilometres (110 miles) across in the crust beneath. Shock waves blasted upwards, tearing the atmosphere apart and expelling over a hundred trillion tonnes of molten rock into space, later to fall across the globe. Almost immediately, an area bigger than Europe would have been flattened and scoured of virtually all life, while massive earthquakes rocked the planet. The atmosphere would have howled and screamed as hypercanes five times more powerful than the strongest hurricane ripped the landscape apart, joining forces with huge tsunamis to batter coastlines many thousands of kilometres distant.”

“A Guide to the End of the World”, Bill McGuire (2002)

The ‘Chicxulub’ impact was the catastrophic event that forced the extinction of much of Earth’s biology. The life that wasn’t instantly extinguished upon impact would die in the weeks and months of acid rain, falling debris, plummeting global temperatures, shuddering earthquakes, tempestuous weather and raging wildfires to follow.

Or in the subsequent years of icy nuclear winter.

Or in the years of solar radiation exposure caused by the Earth’s disintegrated ozone layer.

Yeah, sucked to be prehistoric.

Class Dismissed: Your Take-Home Message

(Really bad) diagram showing the orbits of known Earth-crossing asteroids. The four white dotted circles indicate the orbits of our solar system’s four inner planets, Mercury, Venus, Earth and Mars. The sun lies at the centre. In reality, this picture should be completely pink from the number of asteroids there truly are orbiting our sun. But Google wasn’t playing nice with me today.

Our universe, galaxy and solar system are swarming with lost and wandering bits of space rock. Some have managed to find a gravitational focal point to orbit around and we see these visitors from our vantage point here on Earth with accurate predictability. A perfect example would be Halley’s Comet, which we see once every 75, 76 years. Others wander our solar system far more eccentrically, although the gravitational pull of our Sun and planets do affect the path they travel.

The take-home message is that we, just like every other planet or moon in our solar system, are just as vulnerable to a catastrophic meteorite impact. We are not safe on our little blue planet. We have suffered in the past and we will suffer again in the future. Life here is precious. So make sure you appreciate it the way it is now, because tomorrow you might not have time to reattach your bikini top before a shockwave so f&*king inconceivable in size and rage hits, I will be forced by sheer necessity to use a curse word as an adjective to describe it.

… run?