h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Movies that depict a worldwide catastrophe are usually scoffed at, probably because there's always some big yank hero who saves the planet. It's the yank saving the planet that's the bit that's hard to believe, not the catastrophe. "The Day The Earth Caught Fire" had no such hero and neither did "The Day After Tomorrow", and both ended with a question mark.

Our planet is popularly regarded as pretty tough and indestructable, but that is a gound level view. To get a better idea of how vunerable our planet is, we need a model.

The Earth is about 8,000 miles in diameter and the average thickness of the crust is about 25 miles. So let's represent the earth with an every day object on a scale of one mile to one thousandth of an inch. How about a small plastic beach ball.

Our model earth is 8 inches in diameter and has a skin or crust 25 thousandths of an inch thick (that's a fortieth of an inch). If we inflate the ball so it is just about full of air but not enough to stretch the skin. Pretty squidgey isn't it. The plastic skin is probably far too tough to model the earth's crust and a better candiddate would be a 40th of an inch of cold fat that solidifies and floats on last night's fry up! If you've every played with fat as it starts to harden, you can get some pretty impressive crumple zones that look just like little mountain ranges.

Inside our Earth model we have yesterday's rice pudding heated up and squeezed into a ball and in the centre, a golf ball representing the core.

Now dust the outer surface with a thin layer of talc, which represents the biosphere. That's the bit where life hangs out and isn't much more than a thin layer of green scum that could be wiped away in an instant.

I've left out the sea, but by now you should be able to imagine how fragile that is too. Remember that the North Sea is only about 90 feet deep, so on our model's scale, it's just a smear.

There aren't enough craters on the Earth's crust to reflect the intensity of bombardment from space that would have occured since the surface first solidified. The current explanation is that now and then, lava oozes from the mantel and creates a new surface, filling in most of the old craters. All the land masses on the earth are on the move, buckling up the crust to make mountain ranges and sinking down into the mantel to be recycled.

With all this going on, it is certain that life may have risen several times and been annihilated. We live in one of the relatively quiet periods in between.

Mass destruction can be caused by other than geological forces, and can be caused by life itself just going about its day to day business and doesn't include nuclear bombings.

For those who have made wine at home, you will have mixed up a nice rich soup of fruit-pulp, sugar, water, nutrients and yeast. The plan is that the yeast uncontrollably multiplies its population consuming the riches of its world, peeing alcahol and farting carbon dioxide until it chokes and poisons itself to death. Scale that up and we have a pretty accurate model of the human race to put on our model earth.

On our scale model Earth, the atmosphere is about one hundredth of an inch thick and the bit our model human race lives in is the bottom hundredth of that. It wouldn't take much to screw it all up would it?

It isn't taking much to screw up the real world either!

Thanks very much for your breakdown of the fragility of Earth; one of the pleasures of "The Day the Earth Caught Fire" is because it ends, as you said, with a question mark.
A while back, I was "chugged" and now give a monthly contribution to Friends of the Earth. I also do other worthy, middle-class Guardianista stuff like recycle what I can, use energy-saving lightbulbs, eat organic, etc. etc. I tell myself that at least doing a bit is better than doing bugger all - but then that other voice, the voice of cold reality, tells me to wise up.
Given how difficult we seem to find it to evolve beyond the "war = a necessary evil" type of thinking, perhaps something on the scale of DECF or DAT is called for to shake us into universally supported strategies to protect the planet. Clearly hurricanes and tsunamis ain't enough.

On TV today, they were batting on about how the Greenland ice cap is melting. This was followed by a young lady sitting in the studio telling us how taking out bottles down to the bottle bank can make all the difference. Utter piffle!

I did an OU Science Foundation course during a boring phase of my life. The course contained the results of a meticulously run study into bottle recycling. The conclusion drawn from this study was that it was a complete waste of time recycling bottles because it actually costs more time, money and energy to recycle used bottles than it does to make new ones.

The cold fact is, that it ALREADY IS TOO LATE. Global change is in progress and is unstoppable.

If we look at what the climate consists of, we will understand why.

The Earth's climate can be imagined as huge wallowing rubber bags containing trillions of tons of air, water, dust and the rubbish thrown up by mankind. The huge bags jostle each other, squeeze past, over, under and through each other trying to find somewhere to rest. In doing so, the pressure in the bags varies and produces what we know as weather.

Mankind has produced a lot of filth and upset the "normal" activities of these big wallowing bags and so the bags act in a similar fashion to adjacent tectonic plates. Both these system are fluid systems. They "like" to flow evenly and smoothly and not cause too much fuss. If a jam occurs, part of the system gets held back whilst the rest of it trogs on as normal.

The energy in these systems is enormous, and so when something happens to stop them flowing, the stress built up around the impeded area is collosal.

The driving force is unstoppable and eventually something has to give. When it does, the bit that has been held up has accumulated all the energy that would be required to move the system along gracefully and the time it would take to move the distance it lags behind is also compressed, so to regain normality, a catch up operation occurs and all that energy and all that mass is released in a compressed timeframe and we have an earthquake or huge storm. Further problems will occur if we end up with a bag of atmosphere containing weather in the wrong place.

If you want to do a simple experiment to visualise this, it just takes a reel of cotton, a packet of balloons (of different colours is best) and a piece of fur - your cat will do!

Inflate all the balloons and knot the input tube off. Next, tie lengths of cotton or knitting wool, about a metre or a yard will do, to each ballon. You can leave 'em on the floor for the moment. Now take your fur (some fabrics will work too) and give one of the balloons a good rub with it. This will impart an electostatic charge onto the balloon. (You may have done this before in performing the old "balloon sticking on the ceiling trick).

You will now need to attach the free end of the cord to something high enough up to keep the balloon well away from the floor. Each balloon will need to be suspended from the same point. Balloons don't react to the earth's gravitational pull very strongly, so a bit of blutac on the ceiling would do the trick. For safety's sake, don't attach anything to any electrical apparatus.

Eventually, you will have a substantial cluster of balloons hanging from the ceiling, but because you have charged them all up, they will all have a an electrostacic field of the same polarity and will repel each other. No balloon will touch any other.

As you added each balloon, you will have noticed that the whole system will adjust itself to accommodate the newcomer and eventually settle down to a balanced system. Any differences in balloon size will be compensated for.

Now you are ready to see what happens if the system is disturbed. A slight waft of air will cause the whole system to wobble about, but it will eventually settle down to the way it was. You could cause othe disturbances with a hairdryer or a bowl of warm water on the floor underneath, but provided the disturbance is gentle, the system will remain stable. However, if the disturbance is stronger, you may find some balloons will change position. This is where different colour balloons are useful - or you could use a fibre highlight pen to mark them. Having managed to change the position of one balloon, you will find it somewhat difficult to get it back in its original place using the same method you used to relocate it. If more than one balloon changes position, the problem is compounded making very unlikely that you will manage to restore the system to its original state.

If the balloons represent the big wallowing bags of air I opened with, you can see how easy it is to make them act abnormally and what the consequencies of pushing the system too far can be.

It would take an awful lot of effort and a lot of luck for the system to restore itself to what we regarded as normal. In our model, the change in position of one balloon was a challenge, the change in position of two or more balloons produced a system so different to the original and so more difficult to restore, that when mapped to the real world it represents a catastrophy that may NEVER go away.

As far as the real world is concerned, I fear that we already have one balloon out of place!