20+ Fun Geology Facts

Once upon a time I earned a degree in geology ... then came the oil glut (am I ever aging myself!) and I moved on to other careers.  These days, I retain just enough geology trivia to amuse my middle school students.  Here are some of my standards:

1. Rubies and sapphires are actually the same mineral - corundum.  The basic chemical formula of corundum is Al2O3, but traces of iron stain the mineral red (ruby) while traces of chromium or titanium stain the mineral blue (sapphire).
2. Rubies, sapphires and emeralds are all more rare than diamonds.
3. Not all diamonds are clear.  They come in a variety of colors (called "fancies"), including yellow, green, blue, orange, brown ("champagne"), purple, grey, black (called carbanado, recently shown to be meteoric), milky white, pink, and red.  Red is the rarest.  
4. Antacids taste like chalk because they ARE chalk, a.k.a. calcium carbonate.
5. There are 18 volcanoes in the US with the potential to erupt again, all of them in Alaska, Hawaii and the West Coast states.
6. Will Yellowstone spawn a "super volcano" that will destroy the US?  ANSWER: Probably not.  The amount of rhyolitic magma just beneath the surface of Yosemite is relatively small at present, so even if it eventually "erupts" through the surface, should cause minor lava flows rather than a large super volcano-type eruption. (For those who are still hoping the Mayans were onto something, however, a super volcano-type eruption is technically possible.  USGS sets the odds of such an event occurring in the next few thousand years at 0.00014% .)
7. The Gulf of California is a spreading zone - many millions of years from now, it will be an ocean.
8. The earth is slipping along the San Andreas fault at a rate of about 2" per year.  This means that in about 15 millions years Los Angeles and San Francisco will be neighbors.
9. California is sinking at a rate of about 4" per year. But you can't blame the San Andreas fault for this one; rather, sinking is due to pumping of natural underground water reservoirs.
10. There's a "failed" rift line - known as the New Madrid Seismic Zone - that stretches from Indiana to Arkansas. Though this rift was not extensive enough to split the North American continent into two parts, the area remains geologically active and is likely to spawn one or more major earthquakes in the near future. (According to USGS, there's a 25-40% chance of a ~6.0 magnitude event in the next 50yrs.) 
11. The Great Lakes, combined, contain more than 20% of the world's available fresh water. (Doesn't count underground aquafers or polar ice)
12. There are only 4 Great Lakes, not 5. Lake Huron and Lake Michigan are actually one continuous lake that we have arbitrarily decided to treat as two separate entities. Together, they form the largest lake in the world - larger than Lake Superior, which is often credited with being the largest freshwater lake in the world. 
13. People experiencing earthquakes in the Great Lakes region have the glaciers to thank - the earth there is still "rebounding" from having been smushed by glaciers during the last ice age. ("Smushed" isn't actually a geological term, but it should be.) 
14. What country owns Antarctica? ANSWER: No one - there's a treaty that establishes Antarctica as a "neutral zone" ... though no telling how much longer this will go unchallenged, since melting due to global warming has begun exposing huge oil and mineral reserves beneath Antarctica's surface.
15. Despite what you've seen on Christmas cards and holiday specials, it rarely snows at the Earth's poles, because cold air is lousy at retaining moisture.  For this reason, both the Arctic and Antarctica are classified as cold deserts.  Overall, Antarctica receives more snow because it is surrounded by ocean (ice in the Arctic is ~2 miles thick); the Arctic, in contrast, sits in a virtual land-locked lake, and sports a mere 15 feet of ice.  This explains why it's possible for portions of the Arctic to disappear (melt) during summer months. 
16. People who wade into the Dead Sea automatically float.  Dissolved salts make the water so dense, humans are less dense in contrast and so float.
17. What is the most earthquake-prone state in the US? ANSWER: Gotcha!  It's not California, but Alaska (see Item #3).
18. What is the most dominant element in the air we breathe? ANSWER: Gotcha again!  Our atmosphere is 80% nitrogen.
19. Iceland looks huge on a regular map, but it is approximately the size of Kentucky.  This is because the Mercator projection map we use to make lines of latitude and longitude lie flat inadvertently makes countries nearer the poles appear HUGE. 
20. The Appalachian Mountains and the Scottish Highlands were once part of the same mountain range, before plate tectonics separated them.
21. Most mountain ranges on Earth are gradually diminishing due to erosion and weathering, but the Himalayan Mountains are still growing. 
22. Why doesn't the earth have as many craters as the moon?  ANSWER: We do!  Geologists have so far located ~170 impact craters on Earth. However, they are hard to spot because many of them have been gradually eroded away or been overgrown by vegetation. 
23. About 200 million years from now, Asia and America will collide to form a supercontinent centered around the north pole.  Scientists already have a name for it: Amasia. (Because apparently scientists are better at predicting stuff than they are at naming stuff.)
24. Every so often our magnetic poles "reverse" - the north pole and the south pole reverse their magnetism.  Scientists estimate this could happen again about 1000-2000 years from now ... So start relabelling your magnets now!