Fossil fuels are energy sources that are formed from the remains of ancient plants and animals. They include coal, oil, and natural gas, which were created over millions of years through heat and pressure applied to organic materials in sedimentary rock layers. These fuels are considered non-renewable because they take so long to form and cannot be replenished quickly enough to meet human consumption rates. They have been the primary source of energy for modern society, driving transportation, industry, and power generation. However, their use contributes significantly to greenhouse gas emissions and climate change, leading many countries to seek alternative sources of energy or implement policies aimed at reducing fossil fuel usage.