Today's mini lecture looks at earth spheres and the interaction among them. An important concept in geology is the interaction of earth spheres to drive geologic processes. Things like the climate system, the plate tectonic system, ocean circulation, all involve all the parts of earth spheres interacting together. What are the earth spheres that we're talking about? Geologists define four, sometimes five.
The biosphere, which includes all living things, including decaying organic matter. The geosphere, which is the solid earth and the loose debris at the top. The atmosphere, which is all of the gases.
And the hydrosphere, which is all of the water, including ice. Now some people will pull out the cryosphere separately and discuss ice separately. Depending on what problem you're trying to solve, it may be very valuable to do that. Note there's some gray areas, things like soil. Does that belong to the...
biosphere because it has decayed organic matter in it, or the geosphere because it's turning into something non-living? And what about clouds? Where do they belong?
Well, we'll get into those philosophical questions later. Now it takes a lot of energy to run Earth, so where does the energy come from? Two sources.
One source is the Sun. This is the external heat engine of Earth and it provides the vast majority of energy that run Earth systems. And the Earth's... internal heat engine, which is the heat from the core, is a very small part, but an important part, of Earth's energy as well.
Let's start with the sun, the external heat engine. This, by the way, is a photograph of a sunspot. Sun provides energy that runs most of the processes that happen on the Earth's surface. The atmosphere and the hydrosphere and the biosphere are all strongly affected by the sun. How much energy does the Sun provide?
Well, incoming solar radiation at the edge of the atmosphere is about 340 watts per meter squared, and at the surface of the Earth, about 240 watts per meter squared. What is a watt? Do you all remember?
You learned about this in physics class, I'm sure. Watt is an energy unit per time. So when we talk about 340 watts per meter squared, time is already in there. What about Earth's internal heat engine?
Well, heat flow from the Earth is measured in microwatts per meter squared. Remember the solar radiation in watts per meter squared? So this is a very small piece of the overall heat budget on Earth, but it's very important. Heat flows out of the Earth at places like volcanoes and other warm spots, and so it's unevenly distributed around the Earth. And it comes from two sources.
One source is just the cooling of this original molten hot Earth, and the other source is radioactive decay. Let's take a little aside to looking at scientists'view of the age of the Earth. One of the first things that someone tried to do to apply science to discovering the age of the Earth was Lord Kelvin trying to determine the cooling of a molten ball the size of Earth to current temperatures. Lord Kelvin, you probably know the name, we use Kelvin as a measure of temperature. So he knew what he was talking about when he was talking about heat flow.
And he applied... his calculations of cooling to an Earth-sized object starting out molten and ending up at the temperature today. And he might have been right if he'd known about radioactive decay, but he didn't, so he came up with an age that was substantially too short.
Radioactive decay provides heat in an ongoing way throughout the Earth and keeps the Earth much warmer than it would have been had it simply been cooling over time. So, heat from the Earth... a little bit, plus heat from the Sun, a whole lot, provides the energy that powers the interaction among Earth's spheres.
And what does that look like in something complex? Well, here's a picture of the climate system, and you can see all of these pieces together in one sketch. You can see the Sun and volcanic activity providing energy to drive the system. You can see the geosphere and the biosphere and the hydrosphere.
and the atmosphere and all of the arrows pointing back and forth indicating how matter and energy move among these spheres to make the climate system work. You're going to work on a jigsaw today that asks some of these questions. How do these spheres interact in complex problems like climate?
Have fun!