This week’s digest contains, I hope, a little fun as well as some useful information. I go on repeatedly (and at great length) about how the Earth is a system and this week I want to spend part of the digest, at least, looking some of the largest-scale processes on the planet and some of the tiny components which influence them.
I won’t be neglecting news, though. There will be the usual quick update on Kilauea, and a check on levels of earthquake activity.
Plate Tectonics: What If…?
Historians (some of them, at least) like to play games about what would have happened if something had been different in the past. What if Hitler had died in the First World War? What if America had never entered the second? What if Catherine of Aragon had given Henry VIII a living son?
Geoscience doesn’t lend itself to speculation in quite the same way, largely because it’s not about choices, but there’s no shortage of theorising about might what happen in the future. One such piece of research was covered in National Geographic this week.
The snappily-titled “Extrapolations of secular trends in magmatic intensity and mantle cooling: Implications for future evolution of plate tectonics” may not sound terribly exciting but it is, and the NG helpfully transcribes into more accessible — and rather more sensationalist — language: “Here’s What’ll Happen When Plate Tectonics Grinds to a Halt”.
Plate tectonics is the major constructive and destructive force on Earth. In simple terms, the heat generated by radioactive decay within the planet drives convection currents which break the crust into plates. Those plates move across the surface.
They are responsible for earthquakes, for (most) volcanoes, for the oceans and continents and the cycle of formation and reformation of these. They influence the ocean circulation and the atmosphere.
But to go back to the beginning. This movement derives from radioactive decay and eventually, the heat supply will stop. What then?
The research paper itself is behind a paywall, but the NG’s report on it is accessible, interesting and informative. What will happen? Well, all the things I mentioned above, plus some others such as the carbon cycle, will stop. There will be no more mountains, though erosion will continue. There will be no more earthquakes. There will be only occasional volcanism, and even that will eventually end.
“The planet will just keep getting flatter and more boring”, says the NG, cheerfully. Not a lot to look forward to, but by then — no-one knows how long, but probably a billion years or two — there will be no-one around to care.
The Mineral Cup
In my early geoscience digests I — and I hope you — got a lot of entertainment out of various Twitter cups, where the Twitterati are encouraged to vote for their favourite (biscuit/film/mountain/whatever) until a champion emerges. We looked at earthquakes and at volcanoes, and now we’re back with the reincarnation of my favourite — the Mineral Cup.
Minerals are important because they are the constituent parts of the Earth. They are inorganic, naturally-occurring, crystalline substances. If you know the constituent minerals of a rock, you can tell a lot about where it comes from — for example, if a volcanic rock erupted from a hotspot volcano or from a subduction zone.
You will know and use a lot of minerals, but there are plenty of others which you probably won’t have heard of. The mineral cup gives an opportunity for learning about them. If you look at the contenders there are some surprises.
You will find diamond there (though I’m afraid it’s already out, trounced in the first round by last year’s winner, olivine). You will also find ice, which is a bit left-field, and I had to look it up to satisfy myself that it is, in fact a mineral (and it is, but only when it occurs naturally, as snow or frost, not when you make ice cubes in your freezer).
I will be using the opportunity to discuss some of the minerals as the cup progresses. And I shall declare an interest. Last year I was rooting for olivine, the eventual winner. It’s a beautiful, green mineral which occurs in rocks derived directly from the mantle. It makes up much of the planet’s mantle. Olivine is a strong contender and I expect we shall hear much more of it. In the meantime — pick your favourite, read the threads, and vote.
The News Roundup
The Earth system might be constantly moving but it isn’t moving at a constant pace.
In past weeks I’ve discussed an apparent upsurge in earthquake activity, and this week that activity had died down again, a result of natural variation. Yes, there were earthquakes — the United States Geological Survey’s real time earthquake map includes 89 of at least M4.5 for 30 August-5 September 2018 — but the largest of them registered M5.9.
Similarly, the Global Volcanism Program update reports new activity at four volcanoes, including two notorious ones in Krakatau and Etna, but Kilauea, though still erupting, has dropped off the list of weekly highlights and may be in the final phase of its current eruption, at lest in the Lower east Rift Zone.
The laws of physics dictate the plate tectonics will eventually grind to a halt, but until then, the process of the Earth will ebb and flow on different scales.