Presentation: no place like home

Our planet--Earth--totally rocks. 'Nuff said. (Video link: "All Alone in the Night - Time-lapse footage of the Earth as seen from the ISS.")

What better reason than to understand how it works? You all are caretakers for our planet, so let's make sure to read the owner's manual.

In this presentation we will look in-depth at key features of Earth, in order to "contrast and compare" it with the other terrestrial planets in subsequent presentations.

First, mass.

Let's line up the planets left-to-right from most massive (Earth) to the least massive (Mercury). Earth's moon is not a planet, but we'll include it as a bonus, for it is very similar (yet very different) than Mercury, which will be discussed in the subsequent presentation. What evidence is there that Earth is currently the most geologically active? What evidence is there that Mercury and the moon are the least geologically active today? We have drilled in towards the core of Earth, and yes, it's pretty hot down in there, but we haven't drilled into the rest of these terrestrial planets (and the moon)--what does their lack of geological activity tell us about the temperatures of their cores? Note that core temperatures correlate with geological activity, such that the planets are also lined up left-to-right from hottest core (Earth) to the coldest cores (Mercury, and the moon).

Why do massive planets have hotter cores than less-massive planets? The terrestrial planets are subject to the "turkey/cornish hen effect." Suppose a turkey and a cornish are both taken out of the oven, where they were at the same temperature. Allowed to cool off on the counter for an hour, the interior of the turkey is still steaming when you cut into it, while the cornish hen (being much smaller) has cooled off considerably. All else being equal, large things cool off more slowly than small things. Earth has a hotter core than any of the other terrestrial planets because it is the most massive, and this allows it to maintain its current volcanic and tectonic plate motion activity, compared to the dormant or dead geological activity on the smaller terrestrial planets.

Remember that when compared to all the other terrestrial planets...Earth is pretty damn hot.

Second, plate tectonics.

This is often referred to as "continental drift" for obvious reasons, but the crust under the ocean is also moving around, and being continuously built and destroyed at various locations in order to shift the positions of the continents around. While we're still on the Thanksgiving food theme, what food do you think of when you watch these continents drift? (Video link: "Plate tectonics animation.")

Continental drift (or plate tectonics) reminds me of...gravy. Specifically the skin that forms on gravy, the day after Thanksgiving, where you pull it out of the refrigerator, and slowly warm it back up on a stove, because microwaving your gravy is just wrong. As the gravy gradually warms up, convection currents form, circulating below the gravy skin, pulling sections apart at certain places where warm gravy rises, or drawing together sections at certain places where cool gravy sinks. The next day after Thanksgiving, try this out for yourself, and imagine that we are just living on floating sections of gravy skin.

Midocean rises (or rifts) are where plates are separating away from each other, due to hot rising magma below the crust. This is where new crust is made.

Regions where cool sinking magma below the crust draws plates towards each other, such that they crumple up, forming mountain ranges; or where one plate subducts below the other, such that sinking plate is gradually destroyed.

In the first subsequent in-class activity, you will delve deeper into these tectonic plate motion regions, and also compare the relative ages of different regions of crust.

Third, the greenhouse effect.

Building a greenhouse for plants requires a transparent material such as glass or plastic to let sunlight through, keeping the plants toasty. Our atmosphere is just a big greenhouse, but instead of glass or plastic, certain gases have similar properties, such as carbon dioxide, but also water vapor and methane.

More specifically, a greenhouse material or gas is only transparent to visible light, which passes through and warms up objects below. These warmed objects will emit infrared light, which a greenhouse material or gas is actually opaque to, preventing it from passing through. So a greenhouse material or gas is a one-way street for the sun's energy, letting it through in the form of visible light, but trapping it in the form of infrared.

Earth enjoys a "good" greenhouse effect, as without greenhouse gases it would actually a little too far away from the sun to receive and trap enough energy to be comfortably warm. So a little greenhouse effect can be a good thing.

However, it is possible for there to be too much of a good thing, where the greenhouse effect traps too much of the sun's energy. Here firefighters are called to open up a car with a child locked inside, who is in danger of experiencing too much greenhouse effect, where visible light from the sun passes through the glass windows, warms the interior, which emits infrared, and if a lot of the infrared is prevented from escaping, the interior becomes too warm.

The primary source of greenhouse gases in our atmosphere? Turns out to be volcanic activity, which over time has spewed out vast amounts of carbon dioxide, and that other greenhouse gas: water vapor. And this still continues today.

But the amount of greenhouse gases in our atmosphere is controlled by our oceans, which not only collects the water vapor from volcanic activity, but also absorbs the carbon dioxide.

Think about opening a can of soda or pop, and letting it sit out for a long while. It will become flat, such that most of the trapped carbon dioxide escapes out to the atmosphere. (Thank you for contributing to global warming.) But it won't become completely flat, as there will always be some carbon dioxide in there, as water has a certain affinity for small amounts of carbon dioxide. If you were set out a pan of pure, distilled water exposed to air, due to its affinity for carbon dioxide the pan of water would actually take in a small amount from the atmosphere.

Now consider the vast of amount of water in Earth's oceans, which will soak up carbon dioxide from the atmosphere. It doesn't stop there, as the carbon dioxide in the oceans (through processes we don't have time to elaborate on further) will filter down and be trapped in sedimentary rock. And due to plate tectonics, this rock will eventually be subjected back down into Earth's mantle, conveniently recycling both carbon dioxide and water. So this natural process will control the amount of greenhouse gases present in the atmosphere...

...as long as it is not overwhelmed by man-made sources of greenhouse gases!

This carbon cycle is an involved process you will analyze in another subsequent in-class activity, along with comparing how this cycle went awry for the other terrestrial planets Venus and Mars. You should be able to fill in the first page of this in-class activity by now, and complete the remaining two pages after the subsequent presentation on the runaway planets, Venus and Mars.