Environmental Econ: Crash Course Economics #22

Adriene: Welcome to Crash Course Economics. I’m Adriene Hill Jacob: And I’m Jacob Clifford. Economics is about choices, and how we use our scarce resources. It’s not just about producing and consuming, it can also be about conserving. Adriene: Maybe counterintuitively, economics has a lot to add to discussions of how we can balance our desire for prosperity and growth, with the need to protect our natural resources. Today we're going to look at environmental economics and think about how economics can help us keep our planet livable. [Theme Music] Pollution is going to happen, it’s a by-product of human existence and there is no way that we can get rid of it all. In fact, one of the ways we know about earliest the societies is by looking at their trash heap, something archaeologists call middens, because it sounds better than “dumps.” But the fact that humans produce all kinds of waste doesn’t mean that we have to embrace islands of trash floating in the oceans, a layer of smog over industrial cities, and toxic chemicals in our rivers. For sake of simplicity though, we’re going to focus on one type of pollution: carbon dioxide emissions. They’re one of the primary greenhouse gases.

These greenhouse gases basically blanket the earth and are causing climate change. CO2 levels are the highest they've been for millions years which is why environmentalists consider it a “planetary emergency.” There's a lot of effort going into how to remove greenhouse gases from the atmosphere, how to make cities more resilient to climate change, but in the interest of time we’re going to focus on efforts to reduce the amount of new pollutants getting spewed into our atmosphere. Jacob: The economic solution is pretty simple. Step one, identify the sources of the most air pollution. Done. We know exactly what it is. It’s factories that burn fossil fuels for energy, industries that use oil and coal to produce things, and vehicles with internal combustion engines. Step two, decrease the supply of these technologies and products or decrease the demand for them. That’s it, it’s simple.

But, the implementation of these policies gets complicated. Let’s look at decreasing supply. As we mentioned in the last video, one of the biggest problems with having countries independently enforce environmental regulations is the Tragedy of the Commons. No one owns the atmosphere, so there is very little incentive for countries to keep it clean and switch to expensive green technologies if no one else is going to. It’s not like there is some global environmental police punishing countries for polluting. While a country like Trinidad and Tobago has a huge carbon output per capita, its small population means it’s only producing a small fraction of global CO2. The other option is to decrease the demand for fossil fuels, possibly by finding alternate green energy sources. But we’re already very reliant on fossil fuels, and markets have made the production of those fuels very cheap. So, any new type of energy will have a hard time beating the established system.

So we can either wait patiently for new technologies to develop and get cheaper, or we can speed up the process by manipulating markets with government subsidies, taxes, and regulations. Adriene: In the case of pollution, there are long-term side effects, like climate change, that consumers often don’t take into account when they buy products. Remember negative externalities? When the full cost of a product doesn’t line up with the costs that manufacturers or consumers pay? Pollution represents a market failure — a situation where markets fail to produce the amount that society wants. To address this, some economists argue that government intervention is not only justified, but essential. There are all kinds of different ways intervention can happen — all of them meant to encourage producers and consumers to choose to pollute less.

One solution is for the government to come out and set very specific rules about how much specific industries can pollute. Forget markets. You're gonna follow our pollution rules. Another way governments encourage people to pollute less is by providing price incentives. Those incentives can encourage individuals to make choices that are better for the environment. The government could add taxes to gasoline purchases, or, on the other hand, provide subsidies for people who drive electric cars. Governments can also create permit markets — basically setting a limit on how much firms can pollute, and allowing those firms to buy and sell pollution permits. You’ve probably heard these called “cap and trade”. Proponents of cap and trade argue that it can successfully limit emissions, without creating hard and fast rules that might hinder economic growth.

And, governments can subsidize the development of a specific technology or industry—in an effort to make that technology more competitive with the alternatives. A country might help support the development of solar or wind energy. As of 2014, around 10% of the energy consumed in the United States came from renewable sources, which is pretty much in line with the global average. Current predictions are that by 2040 15% of the world energy consumption will come from renewable sources. But, alternative energy sources, for the most part, just aren’t cheap enough yet, so the majority of our energy is likely to continue to come from non-renewable sources, at least for now. Jacob: We don’t have the time to sit back and wait for new technologies to get cheaper, and there's no guarantee that the technologies that the government picks will be cost effective. Perhaps the solution is not to get rid of fossil fuels, but instead be more efficient with those fuels. But that has drawbacks, too. Some energy economists argue that the expected gains from energy saving technologies, are offset by something called the rebound effect. Let’s go to the Thought Bubble.

Adriene: Let’s say Hank uses a gallon of gas to drive to work everyday. Then, partially to help the planet but mostly to help his wallet, he buys a new fuel efficient car that only takes half a gallon of gas for the same commute. He saves money and there's less pollution. It is a win-win. But the rebound effect says that the benefits of energy efficiency might be reduced as people change their behavior. With the money he saves, Hank might start driving more than he normally would or he might go on a vacation in Hawaii. That leads to more consumption and possibly even more emissions. Also, if greater fuel-efficiency makes driving less expensive it might encourage more people to buy cars and increase the overall use of gasoline. And even if people didn't increase their driving, the new fuel efficiency could decrease the demand for gas, making fossil fuels cheaper and more readily available for other uses. The possibility of the rebound effect doesn’t mean we shouldn’t invest in energy saving technologies. It just means that we have to keep in mind how consumers will behave. It’s also the reason why it's important to have economists involved in the discussion of environmental policy.

The tools of economics can help analyze the incentives and figure out what might work best. Thanks Thought Bubble. Okay, so we’ve identified another problem. But before you get so angry that you kick over a barrel of oil and light it on fire, keep in mind that there is hope. Most countries are actively trying to address the problem of greenhouse gases. The international community has been trying for decades to work together to protect the environment with varying success. There are international treaties that commit countries to reducing greenhouse gas emissions. UN negotiations are underway to create a new climate change agreement — that could be adopted in December 2015. Private companies and governments are also funding research into green technology. In the U.S. the American Recovery and Reinvestment Act of 2009 allocated billions to fund renewable energy.

China is also vowing to clean things up, and, in fact, leads the world in renewable energy investment. So, now that most countries recognize there is a problem, the hope is that they’ll figure out a way, or more likely a lot of ways, to start addressing it. Environmental economists say that is not just governments and producers that need to change, it’s also consumers. Conserving and consuming more thoughtfully likely need to be a part of our daily lives if we want to protect the environment. But just bringing our reusable grocery bags to the store isn’t going to save the planet, even if it says it on the bag. Bigger and more costly interventions like improving insulation and changing thermostats might have more impact, but we need to recognize individual action alone isn’t going to be enough. Industries, governments, and individuals; we’re in this together. Thanks for watching, we’ll see you next week.

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Judicial Review: Crash Course Government and Politics #21

Hi. I'm Craig, and this is Crash Course Government and Politics, and today we're going to talk about the most important case the Supreme Court ever decided ever. No, Stan, not Youngstown Sheet and Tube Company vs. Sawyer. Although, that is one of my favorites. Loves me some sheet and tube. And no, it's not Ex parte Quirin. Although I do love me some inept Nazi spies and submarines. And no, it is not Miller v. California. Get your mind out of the gutter Stan. We could play this game all day, but this episode is about judicial review: the most important power of the Supreme Court and where it came from. Don't look so disappointed. This is cool! [Theme Music] When you think of the Supreme Court, the first thing you think about, other than those comfy robes, is the power to declare laws unconstitutional. The term for this awesome power, the main check that the court has on both the legislative and executive branches, is judicial review.

Technically, judicial review is the power of the judiciary to examine and invalidate actions undertaken by the legislative and executive branches of both the federal and state governments. It's not the power to review lower court decisions. That's appellate jurisdiction. Most people think of judicial review as declaring laws unconstitutional, and that definition is okay. The legal purist will quibble with you since judicial review applies to more than just laws. Appellate courts, both state and federal, engage in some form of judicial review, but we're concerned here with the federal courts especially the U.S. Supreme Court. The Court has the power to review the following: One, Congressional laws a.k.a. statutes! Statutes. Since judicial review is a form of appellate activity, it involves upholding or affirming the validity of laws, or denying it, invalidating the law in question. You might think that the Supreme Court does this a lot, but it doesn't and historically it almost never happened before the twentieth century.

If the court were always striking down congressional statutes, it would be hard for people to know which laws to follow, and you'll remember that one of the main things that courts do is create expectations and predictability. For instance, you could predict that I would eventually be punching this eagle! Another reason why they don't invalidate laws often is that if the Court frequently overruled Congress, the Court would seem too political and people would stop trusting its judgment. If the Court has any power at all, it largely stems from its prestige and reputation for being impartial and above politics. No one has any problems with the Supreme Court decisions, at all. Two, the Court can also overturn state actions which include the laws passed by state legislatures and the activities of state executive bureaus, usually the police.

The power to review and overturn states comes from the Supremacy Clause in the Constitution. Most of the time that the Supreme Court extends civil rights, it comes out of a state action. A good example is Brown vs. Board of Education where the Court struck down the idea of separate accommodations being equal in the context of state public schools. Three, the Court can review the actions of federal bureaucratic agencies. Although, we usually defer to the bureaucrat's expertise if the action is consistent with the intent of the legislature which the Court usually finds it is. The Court almost never strikes down Congressional delegation of power to the executive. Although, you might think that it should. The fourth area where the Court exercises judicial review is over Presidential actions. The Court tends to defer to the President, especially in the area of national security. The classic example of the Court overturning executive action happened in U.

S. vs. Nixon where the Justices denied the President's claim of executive privilege and forced him to turn over his recordings relating to the Watergate scandal. More recently, the Court placed limits on the President's authority to deny habeas corpus to suspected terrorists in Rasul vs. Bush. So, the Supremacy Clause gives the Court the authority to rule on state laws, but where exactly in the Constitution does the power of judicial review come from? Trick question! It's not there, go look ahead, look. I'll wait. See, not there. Wow, you went through that whole thing really quickly. Fast reader. The crazy thing is that the power of judicial review comes from the Court itself. How? Let's go to the Thought Bubble. The Supreme Court granted itself the power of judicial review in the case of Marbury vs.

Madison. You really should read the decision because it's a brilliant piece of politics. The upshot of the case was that Chief Justice John Marshall ruled that the Court had the power to review, uphold, and strike down executive actions pursuant to the Judiciary Act of 1789, and in doing this, to strike down part of that federal law. How he got there was pretty cool. So, Marbury was an official that President John Adams, at the very end of his term, appointed to the position of Justice of the Peace. When Marbury went to get his official commission certifying that he could start his job, James Madison, who was Secretary of State, refused to give it to him. So, Marbury did what any self-respecting petitioner would do, he went to the Supreme Court for a writ of mandamus that would force Madison to give Marbury his job. This is what he was supposed to do according to the Judiciary Act of 1789. What Marshall did was brilliant! He ruled that yes, Marbury had a right to the commission but that the Supreme Court could not grant his writ because the law directing them to do so was unconstitutional.

This is brilliant for two reasons. First, by the time the time the case came before the Court, Thomas Jefferson was President. Those of you who remember Crash Course U.S. History will recall that that less handsome man told you that Jefferson was a Democratic Republican while Adams, Marbury, and even Marshall were all Federalists. By ruling against his own party, Marshall made a decision that was favorable to Jefferson and thus, likely to be supported. The second move was even cooler. Marshall's ruling took the power of writs of mandamus away from the Court, making it look weaker, while at the same time giving the Court the power to declare the law that had granted it the mandamus power in the first place unconstitutional. So by weakening the Court in this instance, like Daredevil going blind as a kid, Marshall made it much stronger for the future, like Daredevil getting stronger in the future. Thanks, Thought Bubble! So that's where judicial review comes from, but that still leaves many questions.

A big question is, why has this ruling stuck around and hasn't been overturned by other laws or later court decisions? Another question is, is judicial review a violation of separation of powers? Some say that it's judges making laws and thus an anti-democratic usurpation of the legislature's power. Let's talk about this rulings longevity first. Remember when I said last time that the Supreme Court rulings are binding in lower courts? You don't remember do ya? You were sleepin'. Wake up! Well, in general, Supreme Court precedents are binding on future Supreme Courts too because of the principle of stare decisis, which is Latin for "let the decision stand." This doesn't mean that future Supreme Court's can never overturn the decisions of prior Courts, it's just that they try very hard to not do it. This idea of precedent is one way that judges can be said to make laws. Appellate decisions are like common law in that they are binding on future courts and constrain their decisions and because they don't have to be grounded in a specific statute.

Other courts have to follow the higher court's interpretation of the law, and this interpretation has the effect of redefining the law without actually rewriting the statute. On the other hand, appellate decisions are technically not common law in that they are only binding on courts, not executive agencies or legislatures. They are, however, signals to courts and legislatures about how courts will rule in the future. Maybe an example will help. If you watch cop shows, or you get arrested a lot, you probably know something about Miranda vs. Arizona which gave us the Miranda Warning. You have the right to remain silent and all that stuff. Hopefully, you've never heard that in person, though. But hey, we're not here to judge. That's what the courts are for! Bahahahaha. Okay.

In that case, the Supreme Court threw out Miranda's conviction because he hadn't been told he had the right to remain silent. Without knowing that he didn't have to talk, he made a confession that got him convicted. The court didn't rewrite Arizona's law but it sent a signal to Arizona's law enforcement agencies, and those in all the other states, that in the future courts would throw out the convictions of defendants who hadn't been informed of their rights. As a result, police procedures changed in every state, and now the police are supposed to read the Miranda Rights to anyone they arrest. So those are the very basics of judicial review. We've probably raised as many questions as we've answered, but that's why we're making a bunch of these videos! So we can teach it all! All of it! Anyway, the big concern for many is that cases like Marbury vs.

Madison, which give courts the power to strike down pieces of legislation, overturn the judgment of the elected representatives that made the laws and violate the idea of separation of powers. Well, that is a thorny issue, but it's one that we don't have time to de-thorn today. For now, understand that judicial review is how the courts work in practice and not necessarily a defined power granted by the Constitution. Just remember, the executive and legislative branches also operate with a lot of implied powers that aren't explicitly granted to them in the Constitution. That's because the governance of the United States has evolved and changed over time to hopefully, suit the needs of the country as they change over time. Thanks for watching.

Crash Course Government and Politics is produced in association with PBS Digital Studios. Support for Crash Course U.S. Government comes from Voqal. Voqal supports non-profits that use technology and media to advance social equity. Learn more about their mission and initiatives at voqal.org. Crash Course is made with the help of these nice people who have the right to remain silent. Thanks for watching. You have the right to stop watching..

World War II, A War for Resources: Crash Course World History #220

Hi, I’m John Green and this is Crash Course World History and today we’re going to talk about World War II. But we’re not going to look at it as a battle between good and evil, but instead as a war for resources, particularly a war for food. Wait, Mr. Green, Mr. Green, what about like Rosie the Riveter and Pearl Harbor and Nazis and Hitler? Yeah, Me From the Past, I mean if the question is was Hitler evil? Then, yeah. But evil people generally can’t, like, cause massive world wars on their own. So instead of talking about, uh, you know, the personality driven model of history, I want to talk about resources, specifically my favorite resource: food. So the story of World War 2 is commonly told as a narrative of good vs. evil, and it is. But we can also look at the second world war through the lens of resource allocation, and I think if we do it tells a story of both causes of the war and one of the ways that it impacted both soldiers and civilians.

The presence or absence of food affected everyone involved in World War II. In the most stark terms, the absence of food led to the deaths, directly or indirectly, of at least 20 million people during those years, as compared to 19.5 million military deaths. Now, of course, both the Nazis and the Japanese were militaristic and expansionist in the 1930s. And they were both definitely motivated by nationalism, but they were also seeking something called autarky. You can remember this term by conjuring the feeling one gets near Thanksgiving: “Aw, turkey”. You can also remember it when thinking about the collapse of the Ottoman Empire: “Aw, Turkey”. Anyway, autarky is a form of self sufficiency in a world where, increasingly, people were reliant on world trade, and that made nations more and more dependent upon each other to meet basic needs. Both Germany and Japan lacked the resources within their borders that they needed to build their growing industrial states, and the resource that concerned them most was food.

And this was a big part of what motivated their imperialist expansionism. Like, Hitler talked all the time about expanding German territory to acquire “lebensraum,” or living space. But what this meant, of course, was agricultural land to feed Germans, that’s what living space is really about on Earth. And most Germans of the time remembered the blockade during World War I, which had led to acute food shortages. For the Nazis, to quote Collingham, “Lebensraum would make Germany truly self-sufficient and immune to blockade and this would eventually enable Germany to challenge British and American hegemony.” Meanwhile, in Japan the need for food was also spurring imperial ambitions. If anything, Japan’s limited space created a sense of crisis and made colonies seem necessary. Like Japanese colonies in Korea and Formosa, taken in the Sino-Japanese war of 1894-1895, provided 20% of the Japanese domestic rice crop by 1935.

And then the Great Depression and Japan’s growing population made the situation appear even worse and probably led to the decision to annex Manchuria after 1931. So the Germans’ plan was to open up Poland, and eventually parts of Russia, to German farmers. The Japanese plan was to resettle farmers in Manchuria to provide food for the homeland. So if the desire for more food was one of the initial causes of World War 2, it also shaped the actual strategy of the war. This was especially true with one of the stupidest decisions of the war, Hitler’s decision to invade the Soviet Union. A German agronomist named Hans Backe put forth something called “the Hunger Plan”, and in doing so convinced Hitler that in order to become self-sufficient, Germany had to invade the Soviet Union. And everyone knows that you cannot successfully invade Russia unless you are the Mongols. Anyway, the plan was the Ukraine and western Russia would be transformed into a huge breadbasket that would feed both the German armies and German civilians. This was never fully implemented, because, you know, the Nazi’s could never successfully nail down all of the territory, but Collingham argues that it was a primary motive for Hitler’s disastrous invasion of the USSR.

And then on the Western front, the so called “Battle of the Atlantic” was largely about shipping arms, material, and food from the U.S. to Britain. This was incredibly important in the opening years of World War 2. Like, Winston Churchill once said that “the Battle of the Atlantic was the dominating factor all through the war. Never for one moment could we forget that everything happening elsewhere, on land, at sea or in the air, depended ultimately on its outcome.” In short, it was Britain’s dependence upon other parts of the world that ultimately made it stronger than Germany’s attempts at self-sufficiency. Starvation never became an issue for the Brits, but fear of running out of food, especially of running out of food for the troops, led to policies that made starvation a reality for many people in British colonies.

In British Africa, for instance, colonial policy forcing production for the war instead of for domestic food consumption meant shortages that were only made worse by wartime inflation. Crop failure in Rhodesia in 1942 meant widespread hunger and famine. And, in an echo of what happened at the end of the 19th century, World War II and British colonial policy spelled disaster for India. Japan had seized Burma in early 1942, cutting off 15% of Bengal’s rice supply. And when harvests failed later that year, hunger turned to famine. Now, the British could have alleviated the suffering but they were afraid to use supply ships that might be needed for the war effort to bring food to starving people in India. When you take into account hunger-associated diseases, between 1.5 and 3 million Indian civilians died, more than the total number of Indian combatants killed in World War 1 AND World War 2 combined. In the United States, meanwhile, there was no starvation, but there was some rationing.

And this was, especially relative to most recent American wars, some shared sacrifice. Americans gave up coffee and chocolate so that the troops could be well fed. So Americans and Britons hardly suffered from hunger. Neither did the Germans, actually, where memories of World War I made feeding the civilian population a top priority. Of course, millions of civilians weren’t being fed because they were being murdered or worked to death in concentration camps. But in Britain, World War II might have actually improved people’s diets. Now, Britons largely despised the whole-meal National Loaf of bread, but it was more nutritious than white bread and its flour took up less cargo space. It’s amazing to think that British people would dislike good food when there’s so much of it in their country. Stan, this is the part where in the comments all the British people say, “We are not a country, we’re four separate countries!” The “dig for victory” campaign encouraged ordinary people to plant gardens, and so they ate more vegetables. Full employment and higher wages meant that working class people also had more access to nutritious foods.

Also, you know, they had the benefit of Canada growing like, a gajillion acres of wheat. Although both the British and the Germans saw an overall reduction in caloric intake, it was nothing compared with what was happening in the USSR, Japan and China. In Russia, daily caloric intake by the end of the war was half of what it had been in 1940. And I will remind you that things were not great in 1940 in Russia, because Stalin. The daily caloric ration for Japanese women workers fell to 1476 calories, which was bad, but in China, where the corrupt Nationalist army was known to sell rice to the Japanese for profit, a famine in Guangdong claimed the lives of as many as 1.5 million peasants. And without doubt, much of the civilian suffering in the war was related to the massive amounts of food needed to keep soldiers fighting. Let’s go to the Thought Bubble. In World War 2, the US and Britain made a massive effort to make sure that their soldiers were well fed, and for the most part it paid off, even though the food that they got was sometimes pretty gross.

The British World War I diet of biscuits and bully beef eventually gave way to the appetizingly named “composite ration.” American soldiers may have complained a lot about their infamous C and K rations, but they were the best fed soldiers in the world, receiving a whopping 4,758 calories per day, including meat at every meal, because, you know… America. As you can probably guess, Soviet soldiers did not fare so well, especially when the Germans invaded because it was their policy to live off the land, which meant scrounging as much food from the Russian countryside as they could. German troops weren’t as well fed as Americans or the Brits, but they still managed to scarf down a respectable 4000 calories per day. No combat soldiers were as consistently hungry, however, as the Japanese. Japanese soldiers were expected to feed themselves and were not provided with field kitchens.

Often this meant that Japanese soldiers were fueled by little more than rice. And as the war turned against them it became more and more difficult for Japanese troops to feed themselves. On Guadalcanal the Japanese attempted to re-supply their troops with floating barrels dropped from passing ships, but by December 1942 between 120 and 130 soldiers were dying of starvation every day. The Japanese commander there estimated that while 5000 of his soldiers died in combat, 15,000 starved to death. Overall, it’s estimated that more than 1 million of the 1.74 million Japanese military deaths were caused by starvation or malnutrition. Thanks Thought Bubble. So, a quick look at the history section in your local bookstore or an IMDB search will tell you that there are hundreds if not thousands of ways to tell the story of World War II.

And this is just one history of the war, certainly not a definitive one. But examining the role of resources, especially food, in the second world war tells a story that has at least one advantage over the narrative of the triumph of Allied good over Axis evil. Because it helps us to see that the war was not only about the soldiers fighting, and it gives us a window into the way the war affected everyone who lived at the time. It also allows us to see World War II from a global perspective in a way that focusing on strategy or tactics or pivotal battles doesn’t. Like very little fighting went on in Sub-Saharan Africa or most of India, but these places were deeply affected by the war in ways that don’t often make it into history books.

Also, we live today in a thoroughly globalized world, but so did the people of the 1930s, and it’s very interesting to see some of their responses to it. That hyper nationalist idea, that we can take care of ourselves and don’t need help from outside, as long as we annex a lot of territory that’s currently outside of us – that idea is a response to globalization. But I think history shows us that it’s a horrible response. It’s a dangerous business when humans imagine others as less, when they think their land needs to become our land so we can feed our people. And in that sense at least, you can’t separate ideology from resource allocation, and as long as we live in a world of finite resources, the potential for conflict will always be there. Knowing that, hopefully, will help us to avoid it. Thanks for watching. I’ll see you next week. Crash Course is filmed here in the Chad and Stacey Emigholz studio and it's made with the help of all of these nice people and also with the help of our Subbable subscribers.

Subbable is a voluntary subscription service that allows you to contribute directly to Crash Course so we can continue its mission of keeping it free for everyone forever. So thank you for making Crash Course possible, thanks for watching, and as we say in my hometown, don’t forget to be awesome..

The Earth: Crash Course Astronomy

The Earth is a planet. That’s a profound statement, and one that’s not really all that obvious. For thousands of years, planets were just bright lights in the sky, one-dimensional points that wandered among the fixed stars. How could the Earth be one of them? With the invention of the telescope those dots became worlds, and with spacecraft they became places. The Earth went from being our unique home in the Universe to one of many such…well, planets. The Earth is the largest of the terrestrial planets, the four smaller, denser, rocky worlds orbiting close in to the Sun. It’s about 13,000 kilometers across, and has a single, large Moon which we’ll learn a lot more about next week. Unlike the other three terrestrial planets, Earth has something very important: Water. Or, more specifically, liquid water on its surface, where it can flow around, evaporate, become clouds, rain down, and then mix up chemicals so they can do interesting, complex things—like support life.

Earth’s ability to sustain life depends on that water. It also depends on Earth’s atmosphere, of course—breathing has its advantages—and both, weirdly enough, depend on Earth’s magnetic field to exist. And that, in turn, depends on what’s going on deep inside our planet. So, let’s take a look. Like the Sun, the Earth is a many-layered thing. At its very center is the core, which actually has two layers, the inner core and the outer core. The inner core is solid, and made mostly of iron and nickel. These are heavy elements, and sank to the center of the planet when it was forming, leaving lighter elements like oxygen, silicon, and nitrogen to rise to the surface. The solid inner core is about 1200 kilometers in radius, or about 10% the radius of the Earth. The outer core is also mostly iron and nickel, but it’s liquid. The material in it can flow. It’s about 2200 kilometers thick. The temperature in the Earth’s core is tremendously high, reaching 5500° C. The pressure is huge as well, as you might expect with the weight of an entire planet sitting on top of it. You might think at such a high temperature, iron would be a liquid, but iron can stay solid if the pressure is high enough.

In the inner core, the pressure is extremely high, and even though it’s hot, iron is solid. In the outer core, where it’s still hot, but the pressure is a little bit lower, iron is a liquid. Above the core is the mantle.It’s about 2900 kilometers thick. The consistency of the mantle is weird; most people think it’s like lava, but really it’s like very thick hot plastic. It behaves more or less like a solid, but over long periods of time, geologic periods of time, it can flow. We’ll get back to that in a sec. On top of the mantle is the crust, a solid layer of rock. The overall density of the rock in the crust is less than in the mantle, so in a sense it floats on the mantle. There are two types of crust on Earth: Oceanic crust, which is about 5 kilometers thick, and continental crust, which is a much beefier 30-50 kilometers thick. Still, the crust is very thin compared to the other layers. The crust isn’t a solid piece, though; it’s broken up into huge plates, and these can move.

What drives the movement of these plates is the flow of the rock in the mantle, and that, in turn, is powered by heat. The core of the Earth heats the bottom of the mantle. This causes convection; the warmer material rises. It’s not exactly a speed demon, though: The rate of flow is only a couple of centimeters per year, so it takes about 50 or 60 thousand years for a blob to move a single kilometer. The hot material rises toward the surface, but it’s blocked by the crust. The magmatic rock pushes on the plates, causing them to slide around very slowly. Your fingernails grow at about the same rate the continents move. Over millions of years, though, this adds up, changing the surface geography of the Earth—where you see continents now is not at all where they were millions of years ago. In some places, generally where the plates come together, the crust is weaker.

Magma can push its way through, erupting onto the surface, forming volcanoes. Other volcanoes, like Hawaii or the Canary Islands, are thought to be from a plume of hotter material punching its way right through the middle of a continental plate. As the plate moves, the hot spot forms a linear chain of volcanoes over millions of years. Volcanoes create new land as material wells out, but they also pump gas out of the Earth too. A large part of Earth’s atmosphere was supplied from volcanoes! The interior of the Earth is hot; in the core, it’s about as hot as the surface of the Sun! Where did that heat come from? Most of it is leftover from the Earth’s formation, more than 4.5 billion years ago. As rock and other junk accumulated to form the proto-Earth, their collisions heated them up. As the Earth grew that heat built up, and it’s still toasty inside even today. Also, as the Earth formed and gained mass it began to contract under its own gravity, and this squeezing added heat to the material. Another source is elements like uranium deep inside the Earth, which add heat as the atoms radioactively decay.

And a fourth source of heat is from dense material like iron and nickel sinking to the center of the Earth, which warms things up due to friction. All of these things add up to a lot of heat, which is why, after all these billions of years, the Earth still has a fiery heart. The outer core of the Earth is liquid metal, which conducts electricity. The liquid convects, and this motion generates magnetic fields, similar to the way plasma in the Sun generates magnetic fields. The Earth’s rotation helps organize this motion into huge cylindrical rolls that align with the Earth’s axis. The overall effect generates a magnetic field similar to a bar magnet, with a magnetic north pole and south pole, which lie close to the physical spin axis poles of the Earth. The loops of magnetism surround the Earth, and play a very important role: They deflect most of the charged particles from the solar wind, and they trap some, too. Without the geomagnetic field, that solar wind would hit the Earth’s atmosphere directly.

Over billions of years, that would erode the Earth’s air away, like a sand blaster stripping paint off a wall. Mars, for example, doesn’t have a strong magnetic field, and we think that’s why its atmosphere is mostly gone today. But we do have an atmosphere, and it’s more than just air blowing around. Earth’s atmosphere is the layer of gas above the crust. Because it’s not solid, it doesn’t just stop, it just sort of fades away with height. By accepted definition—and by that I mean it’s not really science, it’s more of a “Eh, let’s just do it this way” kind of thing—the line between Earth’s atmosphere and space is set at 100 kilometers up. This is what’s called the Kármán line, and if you get above it, congratulations! You’re an astronaut. The atmosphere is, by volume, about 78% nitrogen, 21% oxygen, 1% argon of all things, and then an assortment of trace gases. There’s water vapor, too, almost all of it below a height of about 8-15 kilometers. This part of the atmosphere is warmest at the bottom, which means we get convection in the air, creating currents of rising air, which carry water with them, forming clouds, which in turn is why we have weather. At a height of about 25 kilometers on average is a layer of ozone, a molecule of oxygen that’s good at absorbing solar ultraviolet light.

That kind of light can break apart biological molecules, so the ozone layer is critical for our protection. Incidentally, the Earth’s magnetic field does more than trap solar wind particles; it also channels some of them down into the atmosphere, where they slam into air molecules about 150 kilometers up. This energizes the molecules, which respond by emitting light in different colors: Nitrogen glows red and blue, oxygen red and green. We call this glow the aurora, and it happens near the geomagnetic poles—far north and south. The lights can form amazing ribbons and sheets, depending on the shape of the magnetic field. I’ve never seen an aurora. Some day. You may not be aware of the atmosphere unless the wind is blowing, but it’s there. It exerts a pressure on the surface of the Earth of about a kilogram per square centimeter, or nearly ten tons per cubic meter! There’s roughly ton of air pushing down on you right now! You don’t feel it because it’s actually pushing in all directions—down, to the sides, even up—and our bodies have an internal pressure that balances that out. The Earth also has liquid water on its surface, unique among the planets.

The continental crust is higher than oceanic crust, so water flows down to fill those huge basins. The Earth’s surface is about 70% covered in water. Most likely, some of this water formed when the Earth itself formed, and some may have come from comet and asteroid impacts billions of years ago. The exact proportion of locally sourced versus extraterrestrial water is still a topic of argument among scientists. Earlier, I mentioned trace molecules of gas in the atmosphere. One of these is carbon dioxide, which only constitutes about 0.04% of the lower atmosphere. But it’s critical. Sunlight heats the ground, which emits infrared light. If this infrared light were allowed to radiate into space, the Earth would cool. But carbon dioxide traps that kind of light, and the Earth doesn’t cool as efficiently.

This so-called greenhouse effect warms the Earth. Without it, the average temperature on Earth would be below the freezing point of water! We’d be an iceball. This is why climate scientists are concerned about carbon dioxide. A little is a good thing, but too much can be very dangerous. Since the Industrial Revolution, we’ve added a lot of the gas to our atmosphere, trapping more heat. By every measure available, the heat content of the Earth is increasing, upsetting the balance. It’s melting glaciers in Antarctica and Greenland, as well as sea ice at the north pole. Sea levels are going up, and some of the extra CO2 in the air is absorbed by the oceans, acidifiying them. There’s an old concept in science fiction called terraforming: Going to uninhabitable alien planet and engineering it to be more Earthlike. I don’t know what the opposite process would be called, but it’s what we’re doing to Earth right now.

The Earth is the only habitable planet in the solar system. And you know what? We should keep it that way. Today you learned that the Earth is a planet, with a hot core, a thick layer of molten rock called the mantle, and a thin crust. The outer core generates a strong magnetic field, which protects the Earth’s atmosphere from the onslaught of the solar wind. Motion in the mantle creates volcanoes, and the surface is mostly covered in water. The Earth’s atmosphere is mostly nitrogen, and it’s getting warmer due to human influence.