Notes

PROFESSOR: If you were look at a picture of our planet, you would see that there are many different cycles that are required to function properly for a planet to stay healthy. If you look at our oceans in specific, you would see that they are all connected. Not only are they connected, but if you investigate a little bit farther, you would see that they have currents that all of these oceans share.




Now, all of these currents that these oceans share are called thermohaline circulation. Now, thermohaline circulation is very important to the life on our planet, because it allows nutrients and things like oxygen to be cycled to parts of our planet that wouldn't normally receive those nutrients, such as the bottom of the ocean. Now theoretically, if we were to follow one molecule of




water throughout the entire circulation, it would take about 2,000 years. So this is just one example of things we're going to talk about in this section. Systems of the Biosphere, section one. In this section, we're going to describe the earth's systems in terms of energy, matter, time, and space. And then looking ahead, we're going to explain the




interactions between earth's systems. So earth is a system. And there are four main parts that we're going to talk about that create this complex system. The geosphere, or the rocks of the earth, is the first one we're going to mention. The hydrosphere, or the water of the earth. The atmosphere, the air of the earth.




And the biosphere, which are all living things on this planet. A very delicate balance between these spheres is very important for our survival and the survival of all of our ecosystems. A change in one of these is going to affect all of the others. So let's talk about geosphere first. The geosphere, as we mentioned, are the rocks of our planet.




Now, I'm not just talking about the rock that you skip across that pond, or the ones in your front or back yard. Those are included in the geosphere, but it's much bigger and much greater than that. Land, including the earth's core, mantle, and crust, are all part of the geosphere. And the rocky part of our planet that contacts water, air, and life, or the rocks that interact with other




spheres, the hydrosphere, atmosphere, and biosphere, are all parts of the geosphere. It's an interface between other spheres, which means it's a very central sphere that affects all of the other spheres. A good analogy to draw for our geosphere is that of a dam. If we look at a dam, we'll see that it interacts with many of the other spheres, in fact all of them.




We have a dam that's created out of rocks. We might consider that the geosphere. And obviously, it interacts with water. It collects water behind it, and that is an interaction with the hydrosphere. Now, some of that water that's collected in those reservoirs are going to evaporate into the atmosphere, which is an example of how it interacts with the atmosphere.




Some of that water seeps back into the ground into the water table, and that's an example of how it interacts with the geosphere. And of course, people use that water for things like drinking and to generate electricity, which would be an example of how it interacts with the biosphere. So let's talk about the hydrosphere The hydrosphere is all of the water on our planet.




So if you look at any water on our planet, that is part of our hydrosphere. But once again, it's much bigger than that. It does include oceans, lakes, rivers, groundwater, glaciers, polar ice caps, rain, and snow. But also, it includes some things that might not be so obvious. There is a lot of water in the form of water vapor in our




atmosphere. And that is all included part of our hydrosphere. The water inside plants and animals are also included in the hydrosphere. So we have solid, ice, liquid water, and water vapor in the form of gas, that is all part of this sphere. And it definitely interacts with all other spheres. So one example of how the hydrosphere might interact




with the biosphere is the transpiration of water from the leaves of plants. We've mentioned transpiration in the past, and how it is the idea that water leaves plants through little pores called stomata. And that's just one example of how the biosphere and the hydrosphere are going to interact. The atmosphere.




Well, I think we all know what the atmosphere is. It really is a blanket of air that surrounds our planet. But it's got a lot more to it than just that. It's made up of several different things, including but not limited to, oxygen, nitrogen, water vapor, and ozone. And they all play a vital, important role in our survival.




It extends 348 miles above the earth, but only the part that's closest to our surface is actually visible to us. When you get farther away, it gets so thin that we can't even really see it. Life could obviously not exist without it. It provides protection from things like radiation, which we would be exposed to without that. It also absorbs the sun's energy and keeps us warmer,




helps to insulate the planet. If we didn't have something like our atmosphere, we would have conditions much like we have on the moon, where it's extremely hot on the sunlit side, and extremely cold on the dark side. There are four atmospheric layers that we're also going to talk about later on in this unit. The biosphere.




The biosphere contains every living thing on our planet. Now, that's not just you and I, but it also includes bacteria, plants, animals, everything on our plant that is living. It interacts with other spheres-- as you know, human beings interact with every other sphere-- and it helps to cycle the elements. Things like nitrogen, phosphorus, and carbon are all




cycled in the nitrogen cycle, carbon cycle, and phosphorus cycle. And it is considered a global system, because it definitely includes the entire planet. It's been evolving for about 3.5 billion years, according to the theory of evolution, which is when the first forms first came about. So get real with science.




In 1972, Apollo 17 turned back and looked at our planet. It was the first time they were actually able to take a picture of that. We realize now that earth is a closed system. And earth, everything on this planet is part of a cycle that's been cycling since our planet first formed. All matter and processes are part of the earth system, and the only thing that leaves this earth are things that we




actually send out in space. A few things can enter, things like meteorites and asteroids, but not much. And mostly the stuff that's here has been cycling since the planet started. So thinking ahead to the next section, how would you explain the interactions between each of these systems.


Section 2


PROFESSOR: Scenes like this are actually becoming pretty rare on earth. Due to things such as global warming and climate change, we're seeing our glaciers recede at an alarming rate. But if you'd look into the past, into the history of the earth, you would see that there are time periods where our glaciers were actually advancing pretty rapidly. These are caused by things such as ice ages.




Now, ice ages are caused by the interaction of all of these spheres or systems on earth. And that's what we're going to talk about in this section. The Systems of the Biosphere, section two. We've already described the earth's systems in terms of energy, matter, time, and space. And now we're going to explain the interactions between the earth's systems. So earth is a system that allows life to




exist. So everything works together allowing life to exist. The biosphere, hydrosphere, atmosphere, and geosphere all are connected. A change in one thing causes a change in another. An example of this would be the interaction of organisms of the biosphere and the atmosphere. Plants require carbon dioxide to create their sugar in photosynthesis.




They then release oxygen as a byproduct. Well, you know what? We just happen to require that oxygen. So we take in that oxygen, we use it, and then we release carbon dioxide. So what happens if plants were to disappear? Well, you can imagine that we're going to see a very large increase in carbon dioxide, because there's




nothing taking that molecule out of the atmosphere anymore. So you can see that the biosphere and the atmosphere interact greatly with each other. And a change in one of them is going to change all the others. So earth's systems use feedback to interact. We're going to talk about something called positive feedback and negative feedback in this section.




Humans have altered some of these systems, but it's not always caused by human interaction. Sometimes things like the tilt of the earth can cause ice ages and other actions to form on our planet. So let's talk about positive feedback first. Now, positive feedback is the idea that something is going to change. Let's say something increases. That's going to cost something else to increase, which in




turn caused the first one to further increase, which causes the next one to increase, which in turn causes the first on to increase more. And we're going to see this spiraling out of control. So what positive feedback does is it actually leads to system instability, and it increases change on a planet. So an example of positive feedback are glacial episodes, or ice ages.




Now, ice ages can be caused for many reasons, But some of the main ice ages were believed to possibly have been caused by a change in the earth's axis, which caused sunlight to be not quite so directly affecting parts of our planet. So if we have a change in the earth's axis, we may see some decreased solar radiation. So we may see less of the sun's rays hitting the earth.




Well, if we have less of the sun's rays hitting the earth, we're going to see decreased temperatures. Well, decreased temperatures may lead to increased snowfall, which is going to cause more snow, more glaciers, which is going to allow more sunlight to be reflected from the earth. If you ever think about why do you wear a white shirt during the summer, it's because it reflects more sunlight.




You wear a black shirt, you're going to be hot. Why do you want to wear a black shirt during the winter? Well, because it's going to absorb that sunlight, it's going to help keep you warm. So if we have more snow and more glaciers on the earth, it's going to cause more sunlight to be reflected, which is in turn going to increase our solar reflection. Which is going to allow less solar absorption.




Which is going to keep our temperatures down. Which is going to cause our temperatures to reduce even more. Which is going to lead to more snow and glaciers. Which is going to lead to increased solar reflection and reduced solar absorption. Which is going to happen to reduce temperatures even more. So you can continue that this is going to continue




spiralling out of control until it gets colder and colder and colder, unless something comes in and stops it. Negative feedback is quite the opposite. Negative feedback leads to system stability and it reduces change in an ecosystem. So negative feedback, the Gaia hypothesis is that conditions on earth are regulated by the influence of the biosphere




over the atmosphere. So things like the atmosphere can change the climate of the planet. But the biosphere, or the living things, can actually alter that. It's interesting to think that since the sun was formed, it has increased its solar output. Or it has increased the amount of energy that it sends




towards earth. But the temperatures on our planet haven't increased along with it. Why is that? Well, it's because of the Gaia hypothesis. The fact that the biosphere actually has influence over those changes. So let's look at this for a second.


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The biosphere reacts to change. So if we have increased solar output, we are going to have increased energy absorption, and our temperatures are going to also increase. But let's say we have a field of daisies that are half filled with dark colored daisies, and half filled with light colored daisies. As you know, dark daisies are going to absorb sunlight more




and light daisies are going to reflect it more. So if we have a lot more energy, a lot more sunlight, these dark daisies are going to have a really hard time surviving, because there's so much energy, and they're going to become overheated. So we can expect to see the dark daisies are going to decrease in number. Well, with all that extra space, the light daisies are



then going to increase in number. Well, if we have more light colored daisies, what's going to happen to the absorption of this energy from the sun? Just like wearing a white shirt on a summer day, less energy is going to be absorbed. Well, what's that going to cause? Well, that's going to cause temperatures to decrease. Well, if temperatures decrease and it gets nice and cold,




well, now who has the advantage? The light daisies are going to decrease in number, and the dark daisies are going to increase in number. And so it's going to cause our reflectivity to decrease, because we have more dark colored daisies absorbing all that light, and it's going to start all over again. So by looking at this system, it shows how changes in the atmosphere can actually be held in check by organisms in




the biosphere. So temperatures are going to remain stable because of the way the daisies are reacting to that change. So getting real with science. Glaciers are found on every continent, except for Australia. And most of them are found near the poles. They need special climactic conditions to remain there.




The atmosphere is going to be interacting with the geosphere in order to keep them there. The dense ice turns blue. When we have a lot of snowfall, whether it's from an avalanche or from just snowfall, it's going to become very heavily compacted as this piles up. And as this snow and ice piles up, it's going to squeeze all those air pockets out of it.




And as it does that, it actually takes on a blue color because of the way it bends the light as the light goes through it and reflects off of it. So I'd say once again, we've accomplished our mission. We understand how earth operates as a system of systems. Each of the spheres, the geosphere, biosphere, atmosphere, and hydrosphere, interact closely with one another.




And earth's systems use feedback mechanisms to retain balance, which allows life to thrive and survive on our planet.