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Anthony Teaches Geology

20 days ago
@AnthonyScoffler I do find a lot of things about geology and pretty rocks to be cool and interesting, but I very much prefer reading essay style write ups on the forum rather than Discord, besides the fact the forum is just a better place to archive this stuff for later reference. I think some of this stuff might be of interest to others too, so this is your thread for anything on the subject you feel like talking about. You might be able to answer questions or give suggestions for realism on people's worldbuilding ideas too. (And I still say you should write an educational storygame for kids or something.) If you're getting into mountains and rivers and the like, probably there are people around the forum like Bill who might be able to contribute more knowledgeably than the rest of us just going ooh shiny rock is now shiny wet rock. If you want to show off photos of your rock collection or any other pictures, just dumping them onto imgur and giving us the links is probably best. (The forum can handle pics resized to 700 width and under, so you may or may not be able to work with that...) Anyway, have fun. If any of your students are getting too rowdy in here, just lmk and I'll settle them down with this new shotgun MHD made for me.

Anthony Teaches Geology

20 days ago

Ah, thanks for creating the topic for me, Mizal. I'll be adding some interesting passages soon, and I invite others to do so at their leisure when they have pertinent information to share. We can talk about such topics as the placement of water sources and how it affects civilization, exactly what happens during a volcanic eruption, and much more entertaining perils to throw at unfortunate victims in stories.

Anthony Teaches Geology

20 days ago

How Earth formed (explains some planet-wide processes)

Earth formed from the cold accretion of debris from the solar nebula. About 4.6 billion years ago, it was a ball of magma due to gravity, radioactivity, and meteoric impact. Lighter compounds buoyed to the surface and created distinct zones: an inner core, outer core, mantle, crust, and early atmosphere. This planet-wide phenomenon of buoyancy is responsible for the ongoing convection currents of the mantle. These heat gradients drive seismic and volcanic activity. The movement of metals in the mantle also account for the magnetic field that bends charged particles away from the atmosphere, creating the Aurora Borealis and other solar storm phenomena.

A Mars-sized meteor struck Earth ~4.5 billion years ago, resulting in the formation of the moon (and raising the surface temperature to 2000°C). The existing atmosphere was replaced with carbon dioxide, nitrogen, and water. As Earth again cooled, the water rained down over a thousand years to form the oceans.

About 4.3 billion year ago, Earth was cool enough for life to form. The atmosphere was carbon dioxide and nitrogen; the ocean was acidic with iron. Anaerobic life developed and broke down carbon dioxide. Oxygen was the waste product; it bonded to the iron ions in the ocean to form oxides that fell to the bottom. Organic debris also fell to the bottom, creating layers of chert interleaved with the iron in what's known as a banded iron formation. These account for enormous quantities of iron mined today. After saturating the ocean with oxygen, the atmosphere and surface rocks were subjected to it. This was known as the Great Oxidation Event and gave us our "modern atmosphere". The convenient abundance of oxygen lead to life as we know it.

Anthony Teaches Geology

20 days ago

This is a good book on this subject.

Favorite fun fact: Billions of years ago, an Earth day was only a few hours long and the newly-formed moon was very close above. However, days have been growing gradually longer as the moon drifts farther away from Earth.

Anthony Teaches Geology

20 days ago
nah the days are definitely getting shorter as time goes on

Anthony Teaches Geology

19 days ago
I've read that every time there's a big enough earthquake the day gets shortened by X amount of microseconds, because the planet's axis is affected. I guess if there was enough of them over time or a big enough meteor smacking into us it would make a noticeable difference.

Anthony Teaches Geology

20 days ago
OOooh! That new avatar kicks ass!

On the subject of Geography; it's really awesome for making world maps and the like ^v^

Anthony Teaches Geology

13 days ago

Volcanic activity

Having covered the formation of Earth, discussing some volcanism is a logical next step. Convection currents lead to ascending wells of magma, which may settle below the surface as molten lakes called batholiths. Sections of this lake may rise into layers of rock above, spreading out along weak points where the rock has a lower melting point due to its composition. Magma can rise all the way to the surface in vertical shafts known as dykes. When this happens, the magma that issues forth is called lava. The spilling lava hardens into rock and builds up a mound called a cone. This is a volcano.

It's not all magma reaching the surface, however. As soon as possible, fluids will separate from the melt (on account of weighing significantly less) and course upwards through cracks in the existing (country) rock. They pour out as steam vents (fumaroles), geysers, mud pots and other things you might find at Yellowstone National Park. Hydrothermal vents are responsible for many precious crystal deposits, as well as a few major sulphur deposits. Lava can spill out into air or water; in the latter case, you get an underwater volcano.

Quick fun facts:

  • Calderas occur when the ground above an emptying magma chamber sinks into a bowl-like depression. Remaining magma can escape from the forming ring dykes as the ground gives. This can occur rapidly or gradually. Crater Lake in Oregon, USA was formed from a collapsed caldera. At a depth of 1949 feet, it's the 9th deepest lake on Earth.
  • The Devil's Tower in Wyoming, USA is thought to be a stock (a stumpy extension of a batholith).

Anthony Teaches Geology

13 days ago

Aren't there different types of lava / magma that contribute to the formation of the oceanic and continental crusts (the latter of which tends to resurface up from the mantle)?

Anthony Teaches Geology

13 days ago

The process you're talking about is subduction. It occurs because of tectonic activity, and it's the density of the oceanic plate that causes it to sink while the continental crust "rides" on top.

The oceanic plate is mostly formed of basalts (originating from mid-ocean ridges), while the continents are mostly granitic. The difference is in many ways measurable by the concentration of silica. Felsic melts are siliceous (full of silica). This makes them acidic, causes them to flow slowly, and makes them lower temperature. They tend to have a higher quantity of dissolved fluids. The opposite is mafic. These are basic (on pH scale), less viscous, maintain a higher temperature, and have fewer dissolved fluids. They don't tend to create so many crystals as a result. (There are also intermediate and ultramafic melts.)

Anthony Teaches Geology

13 days ago
The really amusing thing about tectonics is that they're such a basic and understood thing, but 50 years ago they were apparently considered some kind of fringe theory. The geology class I took, the professor talked about how when he was in school he was taught the idea of plate tectonics should be scornfully dismissed. It wasn't until the late 60s that scientists started accepting the idea.

Anthony Teaches Geology

13 days ago

I managed to disclude from my response that the oceanic plate is mostly mafic and continental plates are mostly felsic. In case anyone was wondering why I went off talking about that.