Geology

It happens too often that a six-year old whom I'm nannying asks me something like, "Where does lightning come from?" and I shamefully respond, "Uhhh... it's, you know, it comes from the air... and it's electricity.... something like that." It's exactly like in these Calvin and Hobbes cartoons:

Eventually you start giving answers like these:

So I've decided to write a series of entries that will modestly explain various natural processes. This is not merely to improve my reputation among curious six year-olds, but also to help anyone out there who needs a review of this material, as well.

This entry is about geology. I'll start with a startle: a reminder of our place in geologic time. See the diagram below...

We all know that there are three main geologic layers to our planet: the crust, mantle, and core. The crust is less than 1% of the Earth's mass and consists of oxygen, magnesium aluminum, silicon calcium, sodium potassium, and iron. The mantle is a solid casing and makes up 70% of the Earth's mass. It's made of silicon, oxygen, aluminum and iron. The core is 30% of the planet's mass and consists of iron and nickel. The outer core is liquid and the inner core is solid.

Now for the most important factor in geology: rocks. There are three main types of rocks: igneous, sedimentary, and metamorphic, and they all partake in the "rock cycle," by taking form, wearing down, and forming again. Igneous rock is formed by solidified magma (hence it's name, meaning formed by heat). It's shaped how we normally think of a rock-- as a boulder, stone, or pebble. For example, this quartz rock:

Here comes a fork in road, where the igneous rock can either become sedimentary rock or metamorphic rock. If it becomes sedimentary, then with erosion by wind or water it will break down into sediment. That sediment compacts over time into sedimentary rock, which usually contains a good amount of fossils. Seventy-five percent of the crust's rock is sedimentary. Have a look at the layers of sedimentary rock in my Grand Canyon photos from this summer:

If the igenous' destiny be metamorphic, it will be affected by heat and pressure and subsequently have its mineral content transformed. But whichever road that little igneous takes, he still has the opportunity to walk the road not taken, as sedimentary rock can be affected by heat and pressure to become metamorphic rock, and metamorphic rock can be exposed to erosion and redeposited as sedimentary rock. Moreover, all three types of rock can return to their birthplace, as their re-melting produces magma from which new igneous rocks can form. 

But what exactly is a rock? Is it always naturally formed and composed of minerals? Nope. Man makes rock, such as concrete or brick. And many rocks don't contain a trace of minerals, such as coal, obsidian, or the aforementioned concrete. Now I'm hearing that six year-old saying, "what's a mineral?" The short answer is that it is something natural, solid, and not resembling life in the least (aka without carbon compounds). There are three thousand different types of minerals in the world. Most rocks are made of more than two types of minerals.

Some photos of common types of rocks and minerals: 

Minerals

Feldspar

Calcite

Quartz

Iron

Igneous rocks

Granite (contains feldspar, quartz, and mica): 

Carving Mount Rushmore out of granite

Basalt is the most common rock on Earth. It is formed by rapidly cooling lava:  

Columnar Basalt in Turkey

Diorite is found all through the Sierras and contains feldspar and one or more dark minerals, with the feldspar dominant:

Gabbro contains feldspar and one or more dark minerals with the dark mineral dominant:

Periodotite makes up majority of Earth's mantle and contains mostly iron:

Pumice is formed when lava dries containing air bubbles. It is the only rock that floats:

Sedimentary Rocks

Coal does not contain minerals, but rather consists of carbon. It forms in areas where many decomposed plants and fossils are present. For example, there is a lot of coal and other natural fuels in Canada because a large sea once covered that area and the climate was tropical. 

Shale is hardened clay. It often breaks off into large flat sections.

Sandstone is a soft stone that is usually deposited as many different beautiful layers of sand.

Limestone contains calcium carbonate and lots of fossils, often seashells. This is prevalent in my seaside hometown of Santa Cruz, the most important limestone mining and processing area in the United States during the 19th century.

Metamorphic Rocks

Slate is transformed shale.

Marble is transformed limestone.

 Quartzite is a very hard rock.

Some interesting facts:

• Feldspars make up almost 50% of the Earth's crust. 
• Gold is so malleable that you can roll an ounce of it into a hair-thin wire 50 miles long.

• There are some trails left by sliding rocks in Death Valley, California. How these rocks move is still a mystery, but the favored theory is that wind pushes them along the desert floor. 
• The biggest pure-gold nugget was found in Australia in 1869 and weighed 156 pounds.
• Platinum is so rare that two million pounds of ore may contain only one pound of metal. 
• A geode is a dull piece of igneous or sedimentary rock on the outside with beautiful crystals on the inside. 
• The Taj Mahal is made entirely out of marble. 
• Quartz is the most common mineral on Earth. 
• Sand becomes soil when plants start to sprout in it. In other words, soil is sand mixed with decomposed carbon material. Clay, dirt, mud, silt, dust, and humus are all types of soil.

Hope you learned a bit about the things we encounter every moment of the day... for me, the more educated I am on natural processes, the more I appreciate what I see. I went on a run on the beach after writing this entry and thought about all the waves that have crashed and eroded all those stones and all the lives those stones lived as different species of rock and how far they traveled to get to that beautiful little shell-shaped beach in San Sebastián, Spain. 

Next up, trees!