Plate Tectonics: The Ends (and Beginnings) of the Earth, PART 2

World's plate tectonics
Vector diagram indicating the Earth’s major tectonic plates, the boundaries between them and the direction of their motion. A vector is an arrow that physicists use to illustrate the direction AND relative speed of a moving body. I.e. the longer the arrow, the faster a plate moves.

Welcome back to this, the second instalment of our foray into the field of plate tectonics in which we seek to understand how the giant bumping and grinding shards of crust that make up the surface of our planet have helped to shape it, create it, destroy it and give Hollywood directors endless material for disaster movies. In Part 1, we began our journey with a look at convergent boundaries – where two tectonics plates come together causing a fender bender of such epic proportions that it has resulted in some of the highest (Himalayas) and deepest (Mariana’s Trench) topographical features on Earth.

We discussed the difference between continental collisions (where two continental plates crash into each other) and subduction zones (where one denser oceanic plate gets “pushed” underneath a lighter, crustier plate). Both are characterised by plates that are slowly, yet inexorably colliding into each other and both result in some totally awesome environmental features, such as soaring mountain ranges, plummeting ocean floors, city-shattering earthquakes and volcanoes with monstrous cases of indigestion.

explosive volcanic eruption

In this week’s blog, we’ll take a look at the other boundary types and what kind of geological party one might expect to find there…

2. Divergent Boundaries: When Two Plates Pull Apart

At the opposite end of a plate’s convergent boundary, one tends to find a divergent boundary. Here, the prodigious convection currents in the Earth’s asthenosphere (the squishy onion layer beneath the crusty lithosphere) serve to wrench the two plates apart. This exposes the bubbly mess of searing molten rock beneath. For the same reason you want to sew your butt cheeks together when you have a really bad case of “Delhi Belly”, this runny mess of lithic indigestion explodes out from between the plates causing all sort of fun for the neighbouring wildlife.

Plate tectonics, separation
Diagram illustrating what happens at a divergent pla…
Oh, Christ you’ve got eyes.

There are typically two geological features one finds at divergent plate boundaries and just as was the case with tectonic convergence, the resultant landscape depends very much on whether the plates pulling apart make up the continents or the ocean floor.

Mid-Oceanic Ridges 

mid-oceanic ridge
The Bold and Ridiculously defined Temporomandibularly Muscled

When the separation occurs between two oceanic plates, as is the case with the African and South American plate (in the southern Atlantic basin) and the Eurasian and North American plates (in the northern Atlantic basin), you get a mid-oceanic ridge, which doesn’t really look like Ronn Moss posing in the exquisite turquoise waters of some tropic paradise. No, mid-oceanic ridges are a lot bigger, a lot more ripped and far more complex, although perhaps not as emotionally so… and definitely not as annoyingly successful with the ladies.

mid-oceanic ridge tectonics
Whoar! Now that’s what I’m talking about! The Mid-Atlantic ridge in all its ripped glory. More fault lines than hairs on a manly Portuguese chest, more complex than your girlfriend at her best time of the month and more broodingly seismic than her temper after that fight you had when you commented on her Portuguese heritage.

Two plates can’t get away with divorce without some serious repercussions. For one, the divergent motion of the plates releases a whole lot of pressure on the underlying asthenosphere. It subsequently melts in relief, releasing a surface-bound flood of molten rock known as magma, or at least until it actually reaches the Earth’s surface, at which point it becomes known as lava.

Don’t ask me why geologists have to make things so complicated.

This lava cools and solidifies upon contact with the atmosphere or, in the case of mid-ocean ridges, the overlying water, forming blocky solid structures of igneous rock. Over time, the release of magma from the divergent motion of the plates forms wave after wave of new ground in a process referred to as “seafloor spreading”. This all explains why the age of the rock closest to a plate boundary is younger than the rock as little as 100 metres away! Cool, huh?

mid-oceanic ridge photo
Those bulbous rocky rocks are actually solidified magma (or lava) plumes, which have emerged from the depths of the central abyss.

Some of the attractions one might expect to see on a routine exploration of a mid-oceanic ridge include deep gorges and valleys and formidable submarine mountain ranges that are, in height, taller than Mount Everest. When you’re not “oohing” and “aahing” at the fantastic topography, you can “ugh” at the local wildlife.

pompeii-word-bristle-worms-alvinella-pompejana1

This sexy sock-face with nipples for eyes is actually a Deep-sea Pompeii worm, which typically hangs out near the hydrothermal vent chimneys found along marine divergent boundaries. This large sea squishy enjoys black smokers, long walks along the trench and its ambient environment close to boiling point. Hydrothermal Vent Eelpout fish, Giant Tubeworm and the Hydrothermal Squat Lobster are more examples of wildlife that find boiling water totally amenable. In fact, there is a whole community of specialised critters that have become adapted to life in close proximity to blistering, incandescent volcanic vents. 

Rift Valleys

When tectonic divergence occurs between two continental plates, rift valleys can form. East Africa provides us with a beautiful example of this in the shockingly named “East Africa Rift Valley.” I mean, how left field can you get? Here, the splitting apart of the Somalia and Arabian portion of the African plate has caused the ground to sink in a complex series of fault lines. The resultant synclines (fancy geology speak for “valley” or “dip”) can become filled with water, as is the case with Lake Malawi, Lake Tanganyika and Lake Victoria… some of the oldest, deepest and largest lakes in the world.

Lake Malawi_east african rift valley
A bird eye’s view of Lake Malawi: just one of the major bodies of water formed by the divergent motion of two Africa plates causing a physical cleft in the landscape.

“Hold on,” you say. You’ve referred back to the map of the world’s major tectonic plates and there isn’t a plate boundary anywhere near East Africa.

“How observant you are!” I exclaim saccharinely…

The Africa plate is in the process of splitting into two, like a giant amoeba or your mother’s personality when she drinks too much gin. The plate to the east of the Rift Valley is the Somali Plate and the one to the west is the Nubian or Arabian Plate (check out the diagram below). These two crusty offspring are referred to as “protoplates” or “subplates”.

east-african-rift-valley

What other exciting attractions do rift valleys have to offer us other than very old, very large and very deep lakes? Seismic activity of course, which includes all manner of fire, brimstone, earthquakes and highly specialized organisms that have adapted to the heat and the strange chemical environment found around aquatic volcanic vents.

3.    Transform Boundaries: Where Two Plates Rub Together

transform fault boundaryWe’ve looked at convergent and divergent plate boundaries, but what happens along the peripheries of the plate if the “front” is having a head-on collision and the “back” is being torn asunder?

If your guess was a great idea for a blue film, I commend you on your filthy mind. However, “transform fault” was more along the lines of what I looking for.

Transform boundaries are characterised by two plates grinding past each other. Since jagged rock rarely slides easily past jagged rock, this fault line tends to be the source of much rocking and rolling in the Earth’s crust. Every now and then – which is painfully slowly in geological time – one plate gets snagged on the other and they are brought to a strained halt. The pressure mounts as the one plate tries in vain to move on, but is held back emotionally by the other, until, in a sudden Earth-shattering shudder, they become unsnagged, sending the plates shooting past each other.

This is precisely why transform faults are notorious for causing earthquakes. One of the best-known examples of such a boundary is California’s San Andreas Fault (image below), which is currently – as we speak – being torn asunder by the divergent motion of the North American and Pacific plate.

San andreas transform fault
San Andreas transform fault, California

San Andreas fault is also testament to just how stupid humans can be… building a massive city on a fundamentally unstable Earth foundation is a disaster movie begging to be scripted and cast with slack-jawed hunky men and big-breasted, blue-eyed blondes. Although, if you are a film director and find yourself being inspired by this, please consider casting me as the clip-board wielding, surprisingly young, yet double PhD-educated science floozy! I may not have blonde hair, but you know what they say…

You can easily sleep with a blonde, but a brunette will keep you up all night long.

Mila Kunis is scientific evidence of this fact.

Mila Kunis

The disturbing reality about San Andreas fault is that it’s been 107 years since a major earthquake has occurred, which means that all these long years, the pressure between the plates has been building. Sure, there has been a smattering of decent earthquakes in between the 1906 San Francisco event and the present day – the most recent being the 6.0 magnitude Parkfield earthquake of 2004.

Don’t get me wrong, a 6.0 magnitude will leave your martini shaken and not stirred, but according to the latest Uniform California Earthquake Rupture Forecast (kind of like a weather forecast, but for earthquakes), California has a 99.7% chance of experiencing a larger than 6.7 magnitude earthquake in the next 30 years! I.e. you can bank on it.

It gets worse: the chance that this earthquake could achieve a magnitude of 7.5 or more is a frightening 46%. This may seem like a paltry percentage at first, but if your tandem buddy had to suddenly turned to you on a sky dive and tell you there was a 46% chance the parachute wouldn’t unfurl, you’d most definitely soil your undergarments. You can bank on that, too.

Could the next “Big One” finally send San Francisco into sliding into the sea? Is “Frisco” about to become the next city of Atlanta?

Who can say? Only time… and the underlying tectonic plates. Not Enya.

Massive damaging earthquakeClass Dismissed: Your Take-Home Message

Plate tectonics play an incredible large-scale role in shaping the surface of our planet. Of course there is a myriad of smaller scale (both spatially and temporally speaking) factors that mould the mountains you climb over, the oceans you swim across and the valleys you… bungee jump across?… to be with the one you love.

But, plate tectonics are the daddy of global scale change and transformation.

Be in awe!

Mila Kunis actress

So very in awe…

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Plate Tectonics: The Ends (and Beginnings) of the Earth, Part 1

Earth from Space

Is it possible for something that’s spherical to have a physical end or beginning? A ball just keeps going on and on and on and on. No matter how many times you turn it, you never get to any definitive beginning or end. Where does an egg start and where does it end? With the chicken or the egg or the chicken or the egg or the chicken?

Chicken or the eggWell, in spite of its spherical shape, planet Earth has many beginnings and endings and they are found at the boundaries of the colossal shifting plates that comprise its surface! Plate tectonics account for many of the soaring and plummeting landscapes on our planet and it explains a host of our most frightening natural disasters, from spewing volcanoes to shuddering earthquakes. It builds beautiful fertile islands in the middle of vast ocean expanses while ripping the ocean floor apart elsewhere, forming trenches in excess of 10 kilometres deep. Understanding plate tectonics is key to understanding our planet and its dynamic surface, which, as stable as it seems under our feet, is in reality anything but. 

The Earth’s Surface is Divided into Plates

The Earth’s outermost crusty layer is known as the lithosphere (lithos meaning “stone” in Greek) and it can be likened to a giant shell that has been broken into large, rigid interlocking pieces (refer to the image below). These pieces sit upon the warmer and more malleable asthenosphere and basically bumble their time away by colliding into each other, pulling apart and rubbing against each other. They also, you know, support the entire biodiversity of planet Earth in their spare time.

Earth's plate tectonics

Meet Planet Earth’s tectonic plates: Americans and Canadians get the North American Plate, Europeans and Asians get the Eurasian Plate and the penguins get the Antarctic Plate… EVERYONE gets a plate!

The asthenosphere, which is fluid-like and warmer and more pliable than the outer crusty lithosphere, promotes the migration of the Earth’s tectonic plates. Prodigious convention currents of heat and molten magma travel from the bowels of the planet to its surface, compelling these giant puzzle pieces to move. Just like Tree Ents from “the Lord of the Rings” and the cogs in your brain after a heavy night out, these motions are frightfully slow. Some plate boundaries, such as the Mid-Atlantic Ridge, move as fast as your fingernails grow, which is approximately 1 to 4 cm per year. Doesn’t exactly make for riveting viewing, does it?

But over time, patience wins out against the resistance of solid rock and the results are as creative as they are destructive. 

The Three Plate Boundary Types

All of the plates that make up the lithosphere are in constant motion thanks to the giant hot and moist “visco-elastic” asthenosphere upon which they sit. Hot and moist. If you’ll refer back to the map above, you’ll notice that every plate fits snugly into another, much like a giant jigsaw puzzle. Since each plate is in constant motion, one can definitely assume that it’s where they meet – at the plate boundaries – where the party’s at.

The picture below shows us the direction of motion of each of Earth’s tectonic plates. At any given time, one periphery of a plate is wrenching away from another. At the opposite end of the plate, there is a violent collision going on, while the sides are causing iniquitous mayhem as they rub lasciviously against each other. And as the more, erm, experienced will know… friction leads to all sorts of seismic events.

Earth's plate tectonics 2

Map indicating the direction of motion of Earth’s tectonic plates. The red ‘teeth’ indicate where two plates are colliding, which, as we shall find out momentarily, has resulted in the formation of the magnificent Himalayan mountain range (continental collision) and Mariana’s trench (subduction zone). The first is home to the highest viewpoint on Earth (although you might kill yourself getting there) and the second, the very deepest point in Earth’s crust (although, again, you might kill yourself getting there). 

 1.    Convergent Boundaries: When Two Plates Collide

If you drove your car at the rate of fingernail growth into a brick wall, you would have no idea what would happen because you would have gotten out long ago to use the toilet and get married (probably in that order). But hypothetically speaking, in the absence of arseholes to use and arseholes to marry, you’d probably discover that nothing very much would happen in a collision between a brick wall and your car moving at the rate of fingernail growth. Why? Because you’re going too slowly!

BUT! Substitute your car with a billion tonne megalith and that brick wall would be cement dust in… oh a few million years or so!

The convergent boundaries of Earth’s plates result in the formation all sorts of interesting topographical features. Two colliding plates can either become a subduction zone (where one plate – usually the denser one – plummets beneath the other one), or it can become a collision zone. The plate boundaries that are home to continental soil tend to opt for the latter, while the plate boundaries that are home to ocean soil, the former.

Continental Collisions

Plate tectonics, collisionThe coolest example of a continental fender bender on Earth has got to be the Himalayan mountain range, which is home to the world’s highest, most hostile and most abundantly body-strewn slopes.  This formidable mountain range is the product of two continental tectonic plates (the Indian and Eurasian plate) crashing together and forcing each other to crumple and buckle into soaring mountain peaks and plummeting mountain valleys. There are more than 100 mountain peaks in the Himalayas that smash the 7,000 m (23,000 ft.) altitude mark. Mount Everest, the range’s and world’s largest mountain, comes in at 8,848 m… a staggering 29,029 ft. above sea level.

Himalayan Mountain RangeTypical and totally average view on a hike through the Himalayas

Subduction Zones

When two plates collide and the one happens to be heavier and denser than the other, it typically gets forced beneath the less dense plate. Imagine Paris Hilton gets into a fight with Natalie Portman. Who would come out on top? My vote would be on the substantially less dense (and Harvard degree-wielding) Miss Portman.

This kind of active plate boundary is known as a subduction zone and it can form deep-sea trenches that plunge for kilometres into the ocean floor, as well as yawningly vast abyssal plains that are home to a plethora of deep-sea squishies, only a fraction of which have had the pleasure of joining our taxonomy system. The remaining majority have not yet been discovered or named, although one did feature very briefly in the Pixar animated film, Finding Nemo.

Location of mariana trench map The vertical antithesis of the Himalayas is Mariana’s Trench, a deep gash in Earth’s crust in the Mid-Pacific, directly east of Southeast Asia (refer to the map above). Here, the Pacific plate smashes into the Philippine Sea Plate and the former, which is composed of denser, more metal-rich rock than the crusty, silty continental latter, gets forced downwards. There are examples of mid-ocean trenches all over the world, but at 11,000 m (36,070 ft.), Mariana’s Trench is the very deepest. Not even an inverted Mount Everest could fill this gash.

That is a huge gash. 

Marianas Trench depth reference

But wait, there’s more! One plate does not simply get sucked underneath another without the appropriate ceremony! Deep-sea trenches are very good and all, but we want fire and brimstone!

I’m so glad you asked…

The Ring of FIRE!

The ring of fire When one tectonic plate plummets beneath another, it faces the fiery wrath of the Earth’s immensely pressured mantle. This heat causes the hydrous (water-containing) minerals within the plate’s rock to release their moisture. Since water acts to lower the melting temperature, the mantle overlying the subducting plate melts (surprise!), sending plumes of magma towards the Earth’s surface.

Oceanic volcanism subduction These pockets of molten rock tend to become trapped underneath the crusty rock making up the lithosphere, where the pressure builds up. Eventually, all hell breaks loose and you get a volcanic eruption. This can occur either on the ocean floor or on land surface. Sub-aquatic volcanism tends to result in the formation of fiery, volcano-strewn islands, such as the Pacific Ring of Fire. Terrestrial volcanism tends to result in Pierce Brosnan being a hero and other awesome feats such as pyroclastic flows, earthquakes and village-bound lava lakes.

As long as the Earth’s tectonic plates are mobile, subduction will remain an ongoing process. The denser plate is continuously consumed by the continental plate, sending plume after plume of magma to the Earth’s surface, fuelling the ingoing wrath of these lithic pimples.

Stay Tuned for Part Two! 

Want to find out what happens when a billion billion tonne slab of rock rubs against another billion billion tonne slab of rock? Things get seismic.

Seismic events - Earthquake in Japan Stay tuned for next week’s blog instalment – Plate Tectonics: the Ends (and Beginnings) of the Earth, Part 2.

Goodness, Gracious Great Balls of Ice!

Large hailstone damage

Some things on our planet are so ridiculous that when you really think about them, it’s enough to make you go biblical. Frogs falling from the sky, crop circles, giant swirling hurricanes, belching volcanoes, sulphur-based life forms and Paris Hilton’s immense wealth (and equally as immense lack of IQ). And then there’s hail. The fact that the updrafts within a thunderstorm can be strong enough to hold grapefruit-sized hail in suspension is nothing but ridiculous and wholly impressive.

Great balls of ice!

How Hail is Made 

Falling hail thunderstorms

Hail consists of balls of ice shockingly called “hailstones”. You may even say that hail is frozen rain, but it deserves a slightly more complex explanation than that…

Hail is made within powerful thunderstorms or cold fronts. Cold fronts tend to produce smaller hail that might inconvenience your dog’s plans to go do his business outside (thereby inconveniencing your plans to keep your house hygienic). The large hail responsible for denting cars, destroying crops and severely upsetting your heard of cows is typically associated with large thunderstorm systems that are well-endowed in the vertical and are sustained by powerful updrafts. These traits are especially exhibited by the “Big Daddy” of all small-scale tempests: supercell thunderstorms. These you will find all over the world, but most notoriously skipping across “Tornado Alley” during the northern hemisphere’s summer months.

Supercell thunderstorm
Supercell thunderstorm with rotating mesocyclone (*swoon!*). The presence of such large frozen water particles within the cloud selectively reflects light towards the lower energy (green) end of the color spectrum, which is why thunderstorms that produce large hail tend to make the sky appear a ghostly green.

What cold fronts and thunderstorms have in common is that they are both low pressure systems that suck in air and expell it out their rear. Thunderstorms pull in great volumes of warm and moist air, which rise, cool and condense to form towering cloudy behemoths. Yes, cumulonimbus clouds. The air, once cooled, loses its momentum and proceeds to sink towards the ground. Together, these two channels of air comprise the updraft and downdraft zones that sustain a thunderstorm: its lungs if you’ll indulge a bit of poetic licence.

Now, as you know, temperature decreases with height in the atmosphere. That’s why the tops of high mountains are frozen and it’s why you should always, ALWAYS go for a pee before sky diving. At a certain altitude within a thunderstorm, which can soar to as high as the interface between the troposphere and stratosphere at approximately 10 km above sea level, the temperature reaches zero degrees Celsuis – the temperature at which water freezes. Above this 0°C isotherm (an obnoxious way of saying “line of equal temperature”) all the water droplets in suspension are frozen.

The strong updrafts within a thunderstorm sweep water droplets above the 0°C isotherm where they freeze (consult the pretty diagram below). These pellets of ice then fall back down towards Earth in the downdraft zone, plummeting below the 0°C isotherm and defrosting into big globs of water. This is why thunderstorm rain gets you soaking wet in 10 seconds flat. Just like Channing Tatum in “Magic Mike”.

hail-formation-diagram

However, some of these falling frozen pellets of rain get caught up in the updraft zone again and are swept back up above the 0°C isotherm. Only, they’ve gained a layer of water, which they collected as condensation while chilling out below the 0°C isotherm. This additional layer of moisture freezes, forming a new layer of ice over the original ice pellet.

Concentric layers of ice_hailstone
Concentric layers of ice in a hailstone. Just kidding! It’s a microscopic image of a bacterium’s nipple.

This process can repeat itself several times and each time, the hailstone will grow larger and larger and larger as it collects more and more layers of ice. The next time you’re in the middle of a raging supercell storm, run outside, collect a couple of decent-sized hailstones, run back to the tornado shelter, bolt the trapdoor, watch your dad arm wrestle said trapdoor with an F5 tornado, watch your dad lose, resolve to become a hardcore white vest-wearing, tornado chasing sexpot with a serious deathwish. Oh! And remember those hailstones you collected? Cut them open to see those concentric circles of icy awesomeness.

When a hailstone finally gets too heavy for the thunderstorm’s updrafts to hold in suspension depends entirely on the strength of those updrafts. The stronger they are, the heavier the hailstones. This is why larger hailstones are associated with powerful thunderstorms, such as the Midwest supercells that are sustained by incredibly strong updraft zones.

And when hailstones get heavy, it’s time to run for cover.

large hailstone damage

 Sorry Boys… Size Really Does Matter

Farmers are more obsessed with size than that clutch of vacuous floozies and jockstraps in Jersey Shore. Considering their livelihood depends on it (and not their egos), this is easy to understand and empathize with. But, in no other aspect are they more obsessed with size than with hail. The happiness and health of their livestock and crops depend on it.

Some thunderstorms can create hailstones that are big enough to cave your head in. Even if you do have brains. The next time you’re at a party, scoop an ice cube out your rum and coke and toss it at your mate (preferably the one who’s hitting on your girlfriend). Listen to the dulcet sounds of squealing as it clobbers him in the noggin. Now imagine something easily ten times the size of that ice cube falling thousands of metres (or feet) from the heavens. Yup! Ouch.

Largest hailstone on record
Ermagherd! Ferkerng HUGE herlsterne!

On 23rd June 2010, the largest hailstone in recorded American meteorological history fell in Vivian, South Dakota (image above). This great ball of ice weighed in at 0.88 kg (1.93 lbs) and was a staggering (if it had hit you in the head) 20 cm (8 inches) in diameter.

That’s two inches longer than your average you-know-what, tee hee!

 Class Dismissed: Your Take-Home Message

hail_storms-on-road

Hailstones are physical evidence of the incredible air circulations going on inside a thunderstorm. Can you imagine how strong air must be to prevent something that weighs almost a kilogram from succumbing to gravity? I don’t know about you, but that blows my mind in the most delicious way. And so we see that thunderstorms are about so much more than just thunder and lightning and the occasional airborne cow. These bad tempered weather systems can also be that jerk at a party who throws ice at you.

But, then again, you were chatting up his cherry.

About this Awesomeness…

I met Superman through WordPress blogging. He found my humble blog and decided that he liked it enough to pester me with comments. Those comments turned out to funny and clever enough for us to establish a rapport. Before I knew it, we became Facebook friends. With the name “Christopher Reeves” how could I not?

In an effort to coax me out of my hiatus – which I’ve had to take because I’m studying an online course – he has written this exceptional blog post on the literal awesomeness of the oceans. I loved every word of it and I now reblog it so that all of you can enjoy it. I am tickled pink to learn that my absence is noted by my readers (or at least one of them)… and that Superman took the time to write this brilliant and humorous article, which applies the overarching philosophy of Why? Because Science so very well.

That philosophy is: if you make people laugh about science, they’ll understand it.

Seemed Like Good Science at the Time

 

Mars blows. With so much recent hype and excitement about popping a rover on over to our rusty neighbor, we seem to be overlooking a couple of important points. First, Mars is crappy. It’s cold; the air is, well, not air; and most importantly, there are no attractive scientists actually on Mars. Sure, there are the massively important technologies that we have developed as a byproduct of space exploration to get excited about. Space program spin-offs have given us LEDs, temper foam, grooves in the road, and freeze-dried food.  OK, that last part sounded really exciting before I read it out loud. Anyhoo, Mars exploration could provide a mess of dimly lit, red-desert landscape photos for computer desktop backgrounds. It may divulge powerful revelations about our place in the universe. It might even give us evidence of life on other planets, which would be awesome because, well, ALIENS! But…

View original post 1,647 more words

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?

A Glacier in Fast-Forward

Franz Josef Glacier as seen from the valley floor. This 12km-long glacier can be found on the west coast of New Zealand’s South Island, in the Westland Tai Poutini National Park.

 Ever wanted to see a glacier flowing in high speed? No? Never really thought about it? Yeah… me neither. And then I saw this video and it totally blew my mind…