If you’re into astronomy, or just a fan of any science fiction franchise worth its salt, then chances are you’ve heard the term parsec thrown around. But what is a parsec exactly? Basically, it’s a unit of length used to measure the astronomically large distances between objects beyond our Solar System.
Continental Crust
The crust is the top layer of the Earth’s Surface. Did you know that there are 2 types, though? One is called the Oceanic Crust, and the other, the Continental Crust. As its name suggests, the Oceanic Crust is the top layer of Earth that forms the ocean floor. The Continental Crust, however, will be our focus.
We walk on top of and dig down through the Continental Crust when we plant or drill. Even if there is an unstable surface at the very top, like sand, the deeper parts of the Crust are made of harder rocks. The large land masses, continents, have bases made from sedimentary, igneous, or metamorphic rocks, as well as any combination thereof. This shield rock is the oldest known; it’s been tested, dated, and found to have been here for 3,960,000,000 years!
Geologists, scientists who study the Earth, believe that shield rock was created when hot molten iron, known as magma cooled. If their math’s correct, it happened around the time these rocks formed, almost 4 billion years ago, right? Some of those rocks were so big it took a long time for them to cool. So, even if the rocks were formed 3.9 billion years ago, they might not have cooled for quite some time. Many estimate that the Continental Crust wasn’t completely hard for another 60,000,000 to 160,000,000 years.
The top portion of this rock has another name, platform rock. The oldest-known platform rocks are approximately 600,000,000 years old, and can be found in central North America. The sedimentary rock ranges from 1,000 to 2,000 meters thick; that is equivalent to more than a half mile to 1.25 miles. When we put the top and bottom portions of the Continental Crust together, we get what scientists call, a craton. Most cratons are stable and haven’t been damaged by earthquakes or volcanoes for hundreds of millions of years.
Around the edges are the continental margins, mostly created by sedimentary rock originally found in the oceans. How is that possible, you ask? Well, it’s due to earthquake and volcanic activity. In this case, it’s mainly due to a phenomenon called, subduction. You see, the Earth fits together like a puzzle; and, if you try to place the wrong piece into a spot where it fits, but isn’t quite right, what happens? Another piece might pop out of place. Sometimes, a continental margin works its way under the oceanic crust. When that occurs, the oceanic layer ends up on top of the continental margin. This is subduction. The most well-known place for this is along The Ring of Fire, an area that covers the edges along the Pacific Ocean. This is why so many and such violent earthquakes, volcanic eruptions, and tsunamis occur in that part of the world.
Universe Today has a wealth of information on this and other related topics. Here are just 2 of those available. The first is entitled,
Earth, Barely Habitable?.
The second is called, Interesting Facts About Planet Earth.
Universe Today also hosts Astronomy Cast, a science program that covers a variety of subjects. Episode 51: Earth, explains this subject in greater detail.
The Encyclopedia of Earth , by Michael Pidwirny has some excellent information, too.
Sources:
USGS
Science Daily
What is the Lithosphere?
According to the United States Geological Survey (the USGS), the lithosphere is, “the solid outer zone of the Earth comprising the crust and the upper layer of the mantle.”
Also, according to the USGS, the term comes from the Greek word, lithos, meaning, rock, and the word, sphere, which can be any round object, such as a ball, an orange, or, even, you guessed it, a planet.
Wasn’t that helpful? To a Geologist, a scientist who studies the Earth, maybe; but, for us mere mortals, not really. When I think of, “Crust,” I think of the top of a pie. Apple’s my favorite, but anyway, back to the topic. Other times, I think of a loaf of fresh-baked, piping-hot bread, right out of the oven, smothered with honey butter. Oh, it’s so good! Wait a minute! What am I doing? OK, OK, let me make this point so I can forget about food.
When we discuss, “The Earth’s crust,” we’re talking about the outer layer of the Earth’s surface. This is part of the lithosphere. The crust’s made from 3 different types of rock: Igneous; sedimentary; and, metamorphic. Igneous rock forms when cracks in the Earth, known as fissures, break open or a volcano erupts. Both events bring hot, molten rock, known as magma, to the surface, where it cools and becomes different types of rock; what types may depend upon what else mixes with it, how much pressure it’s under, or how much time passes.
The magma, comes from the other part of the lithosphere. It’s released from the upper portion of the mantle. The lithosphere’s responsible for the renewal of the Earth’s surface. When the magma’s released, it becomes known as lava. Other types of rock might be present when the lava arrives; and, since intense heat, pressure, or both can change the rocks from to another, the crust might appear very different afterwords. Some rocks are melted down entirely, and their molten remains may return to the mantle. Eventually, those remains will make another appearance; but, when, or in what form, when all is said and done, who can say?
The lithosphere is very important to the rock cycle. Without it, our planet wouldn’t change. I remember the horrible eruption of Mount St. Helens. The devastation, looked like pictures from Japan, after the atomic bombs hit Hiroshima and Nagasaki; but, I recall hearing later that scientists discovered never-before-seen plant life due to the changes the particles underwent from the pressure, high heat, iron content, and their quick ability to adapt. Like our hearts, the lithosphere keeps our Earth young and healthy.
Universe Today has some other great articles, if you want to learn more about this or similar subjects. One excellent resource is, Earth, Barely Habitable?. Another is, Interesting Facts About Planet Earth.