Hello. In the last video, we learned about the carbon cycle and how sources release carbon dioxide into the atmosphere and sinks absorb or take in carbon dioxide from the atmosphere and store it. In this video, we will talk about one of the largest sources of carbon dioxide -- fossil fuels. We will learn how fossil fuels were formed and how they're used to provide heat, energy, and transportation. And finally, we will learn about the impact of burning fossil fuels on the greenhouse effect. In an earlier video, we introduced the term fossil fuels. Fossil fuels are natural materials, such as oil, coal, or gas, that are burned to create energy. You may know the word fossil; fossils are what remains of plants or animals that lived long, long ago. One example is the impression of a leaf or a small animal from millions of years ago that we see in a rock today. Fossil fuels are also what remains from living things from millions and millions of years ago. Fossil fuels are formed from the decomposition of living organisms. The most common examples are oil, natural gas, and coal. Oil and natural gas were created when plants and animals that died sank to the bottom of the oceans and rivers and were buried by sediment. Those sediments would have been things like stones in sand that washed into the water and then sink to the bottom. After time, there were many layers of sediment, and a great deal of pressure and heat were created. In this intense environment, the remains were decomposed. Compounds are composed of two or more separate elements. So to make a compound simpler, you take them apart, so that each compound has fewer elements. Millions of years later, these compounds became oil or natural gas. Coal is created in a similar way. For coal, it was trees or other plants that were buried in wet swamplands. When the plants died, they fell into the bottom of the swamps. As time went by, more plants died, and they formed a thick layer at the bottom of the water. These layers were then buried by dirt and water. The heat and pressure under, at the bottom of the piles, cause chemical reactions. In the end, after the oxygen was pushed out and mostly carbon remained, the materials that were left became coal. Oil, natural gases, and coal have all played an important part in helping the world develop since the Industrial Revolution, when modern machines were invented to make our lives better. In modern society, many places in the world get their electricity so easily by simply plugging in a cord into a wall, but that electricity must be created somewhere. The largest share of greenhouse gas emissions come from burning fossil fuels, mostly coal and natural gases, to make electricity. In modern society, it is also very convenient and easy to get from one place to another. You can visit another city or another country in one day, but most forms of transportation also depend on fossil fuels. Planes, trains, cars, trucks, ships -- they burn oil products, such as gasoline, petrol, or diesel, to make them run. Factories that make everything that we fill our stores with, such as clothes, toys, electronics, and cars, all use the burning of fossil fuels to make their machines work and to heat their buildings. As we can see, most of us depend on burning fossil fuels for making almost everything we use and taking us almost everywhere we go. But burning so many fossil fuels does have an impact on the environment. It pushes all the carbon dioxide that was stored in the Earth up into the atmosphere in a way that would not happen naturally in the carbon cycle. And as we learned before, carbon dioxide is a greenhouse gas. So when there is more of it floating around the atmosphere, that means more heat is trapped from escaping our greenhouse -- the Earth's atmosphere. In this video, we learned more about fossil fuels: how they were formed and how they are used to provide heat, energy, and transportation. And finally, we looked at the impact of burning fossil fuels on the greenhouse effect. Our next video will be a language focus on cause and effect.