Why I Love Geology
Geology. Boring, isn't it? Rocks arent good at inspiring interest. The very word can send schoolchildren to sleep and their parents to a faraway place behind glazed-over eyes.
And yet, in a poor light, if you squint a bit, you can see a bit of the story that those boring rocks have to tell.
Take, for instance, a rather big but otherwise unremarkable layer of evaporite beneath the Meditteranean. Evaporites - rock salt, for example - are formed when a body of water becomes supersaturated in a mineral. If you pour some salt into a glass of fresh water, then as you would expect, it vanishes - the crystals dissolve and disperse through the water. Keep pouring, however, and the opposite will soon happen. There will come a point when the water is so saturated in salt that it simply won't dissolve anymore, and a thin layer is precipitated onto the surface of the glass.
The same thing happens in nature. There are basins all around the world - like the Great Salt Lake in Utah and the Dead Sea in Israel - where the rate of evaporation is so high that huge masses of evaporites precipitate and form a gleaming white desert. What makes the layer of Anhydrite below the sea bed in the Mediterranean so interesting, though, is the sheer scale of it. A massive two kilometers thick, far beneath the waves, along the whole length and bredth of the sea - from the Nile Delta to the Rock of Gibraltar. What could have formed such a vast deposit?
The funny thing about the Med is that in a reasonable world it really shouldn't be there. It's a dry part of the world. The largest desert in the world is just a short hop to the south, and despite great beasts like the Nile, Danube and Po draining into it, not all that much water gets dumped there every year. In fact, the rate of evaporation in this isolated basin exceeds the rate of supply of fresh water. If it weren't for that tiny neck of water south of Gibraltar connecting the sea to the Atlantic, the Med wouldn't be there at all.
The more perceiving among you will probably know what I'm about to type next. Yes, there was a time when it wasn't.
The African and Eurasian plates are converging - a huge continental collision is ongoing beneath the Med that is pushing up the Alps and fueling volcanoes like Etna and Vesuvius, and it is this, and its effect on the sill of rock beneath the strait of Gibraltar, coupled with global changes in sea level brought about by climate change, that has in the past cut off the Mediterranean from the Atlantic and turned what's now one of the world's favourite holiday destinations into a bloody great desert. There are huge canyons, kilometers deep, now infilled with the sediment of millenia, beneath every single river that drains into the Med, cut by those rivers when sea level was quite a bit lower in that part of the world. Beneath Aswan, in the south of Egypt, the Nile's canyon cuts down to several hundred feet below global sea level. Beneath Cairo, it's 2.4 kilometers deep. What's more, one drying out of the Mediterranean can't account for the vast strata of evaporites beneath the sea. Nope, to produce such thick deposits, it must have dried out 40 times in a million years.
So yes, that's why I love geology. From an unremarkable seismic survey and the presence of a bit of salt, a grand vision of a huge region as it once was has been developed. A world where there was a canyon two and a half kilometers deep where the Nile Delta now is. A world where you could walk from Africa to Europe without having to go the long way round, though you probably wouldn't want to. From that bit of salt, it can be deduced with a certain degree of accuracy that someone, or at least some living thing, saw one of the greatest flash floods in history, when billions upon billions of cubic meters of water came rushing over Gibraltar - the greatest dam burst in history, if you like.
And that's just the start. The Messinian Salinity Crisis, as this massive cycle of drought and flood is now known, began a mere 6 million years ago, and ended a million years later. That's nothing to a geologist. The thin layer of Iridium that marks the impact of the asteroid that killed off the dinosaurs is 65 million years old. The coal that fuelled the industrial revolution was once a huge forest 300 million years ago, when insects with a wingspan longer than you are tall were flying around and eating each other. The oldest multicellular life is a little under 700 million years old. And yet the geological record goes back much, much further - to 3.8 thousand million years ago, in fact, when the Earth was just starting to cool right after the most violent period of bombardment by asteroids the planets have ever experienced. That's why I love geology - it allows you to envisage, from what appear at first to be the most tenuous pieces of evidence, how the world was at millions of different intervals in its history. Or perhaps, its more like a million different worlds, one after the other.
Anyway, if you read all that, I thank you for your patience. Not sure what inspired me to write it. Insomnia, maybe, and a compelling story.
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Originally Posted by Claudius Gothicus
