Energy, biomass and entropy

<v ->In steps six and seven,</v> you learned about mass and energy. And in this step, we’ll talk about how those interact to keep the Earth as an organized system and how it interacts with food webs and natural cycles on the Earth’s surface. So let’s just recap a little bit with mass and energy ‘cause they’re difficult concepts to grasp. And the first law you learned about was the law of conservation of matter, conservation of mass. And this one’s really important because except for nuclear reactions, it means that mass is neither created nor destroyed. What you see is what you get. What goes in is what comes out.

And that’s a really important concept to remember because it means that all the trees behind me, the atoms in my body will all be reused eventually someday in some other form. They’re not destroyed, they stay as the elements they are. But they’re recombined with other elements to make different molecules. Even now as I’m breathing in and out, I’m converting oxygen into adenosine triphosphate, ATP, to make energy for myself. (exhales loudly) And I’m exhaling, I’m exhaling CO2, probably from the sugar I drank this morning in my coffee. So law of conservation of matter is really important. Likewise the first law of thermodynamics says that energy can neither be created nor destroyed. So we’re constantly cycling through energy.

And that energy is being changed as well. So the sunlight you see coming through the trees behind me is impacting on a leaf. And that leaf is converting some part of that solar energy into chemical energy. Other parts of that solar energy are being absorbed by the plant and re-emitted as heat energy. When I drive up a hill, I’m converting the energy in the gasoline, the chemical energy in that gasoline or petrol into heat energy and kinetic energy. And because I’m driving up a hill, I’m also converting some of that energy, that chemical energy into potential energy as well. Because if I run out of petrol and I don’t have any breaks, I’ll roll back down that hill.

So lots of different kinds of energy, they’re listed in step seven. Have a look at those. And just remember that energy is neither created nor destroyed, it’s usually converted into something else. And it’s important for us to always keep track of where that matter and that energy is going because that helps us describe some of the interconnectedness and the relationships that we see in the environment around us. Now, let’s talk about the hard one, the second law of thermodynamics. And this is the idea around entropy. And this is a really hard concept sometimes for people to grasp. And the best way I like to think about this is the bricks on the truck analogy that I used in step seven.

And our world always wants to become a cold gray goo. And the only thing that keeps us from becoming a cold gray goo is the sunlight from our sun and the heat from the earth beneath our feet. And these provide the energy to every day, put the bricks back up on the truck. Now, this is really important because there’s a lot of natural cycles in the environment around us. And they’re really important cycles, whether they’re the hydrologic cycle, which is the movement of water around the Earth’s surface and through the Earth’s atmosphere and sometimes even through the ground itself. There’s also the nitrogen cycle, which is how nitrogen is absorbed by plants through fungi and then re-emitted into the atmosphere.

There’s the calcium cycle, there’s the carbon cycle, every element has a cycle associated with it. And it’s really important because remember, matter is neither created nor destroyed. There’s always calcium in the environment. There’s always carbon in the environment. It’s simply being recombined every time it’s transferred from one system to another, whether it’s transferred from the atmosphere into wood of a plant or if it’s water being evaporated from the ocean’s surface into the atmosphere, and then the atmosphere blows over land where that water is redeposited as rain, brought up into a plant and then incorporated into wood, the hydrogen and oxygen incorporated into the wood.

So all these natural cycles are constantly around us, and they’re constantly being driven and renewed by the sun’s energy and by geothermal energy beneath our feet. Human activities can impact these natural cycles. And a really good example of this is to think about fresh water dams. And the cycle that we’re referring to would be the hydrological cycle. And that’s where water is evaporated off the ocean’s surface into the atmosphere as vapor. When that water vapor is moved over the land’s surface by wind and air occurrence, precipitation can occur, the water falls out of the sky as rainfall onto the ground and then runs off of the land into rivers and streams.

And then humans have developed this technology called dams to trap that water behind a dam so that we can use it throughout the year for agriculture, for drinking water, for a host, for recreation, for a host of different purposes. Now, that dam has actually interfered with the natural hydrologic cycle. And that has impacts both upstream and downstream on the natural systems that depended on that fresh water from rainfall and into that river. Now, it may be that trees along the riparian zone needed that water, it could be specific kinds and species of fish required a certain amount of water in the river to spawn and regenerate. But this is how humans can have an impact on these natural cycles.

And this is part of what we do in environmental science, looking at these impacts. And finally, I want to talk about food webs and energy, food pyramids, energy pyramids, whatever you want to call them. And this is a really interesting side effect of the law of, the first and second law of thermodynamics and the law of the conservation of matter. And really when we think about plants and animals and the interactions they have, I think it’s really interesting to think about the energy it takes and the mass it takes to build a large complex animal like a human or a lion versus the energy and material it takes to build a blade of grass.

And one of the things to think about is that, as you move up the food web from primary producers at the bottom of the food web, things like grass, plants, algae in the oceans, phytoplankton in the oceans, as you move up that pyramid, it requires more energy and more matter to create those next organisms up. So your primary consumers are the ones that eat the grass, they eat the phytoplankton. This could be small fish, it could be grasshoppers or insects. And then you have your secondary consumers, which are the animals that eat those primary consumers. And they require lots of primary consumers to create these secondary consumers. They require more energy and more mass.

And so they’re essentially funneling all this energy and mass upwards until you reach tertiary consumers, which are things like lions, humans, the sort of the top predators that eat things. And so you’re concentrating energy, organization, and low entropy into these top consumers. And I think it’s a really interesting thing to think about, especially when we think about human impacts. We are a tertiary consumer, and so we’re using energy and matter that have been not created but have been modified lower down on that food pyramid. Have a look at this diagram and think about what it means to be a tertiary consumer, especially with respect to matter and energy.