Oil and Natural Gas
Similar to how coal is formed from the compressed and heated remains of trees and plants from ancient peat swamps, oil is formed from small sea creatures and other organic matter which fell to the bottom of ancient seas and was slowly and gradually compressed over time to form oil and natural gas in the form of methane which was trapped in the seabed and shale rocks.
Oil is an extremely useful substance which can be broken down into various components to produce diesel, petrol and kerosene (aircraft fuel), as well as being used to form products such as plastics and bitumen (used for road building).
Also just like coal however, the burning of oil and natural gas produce carbon dioxide which adds to the layer of greenhouse gases around the earth that prevents heat escaping into space, although natural gas is considered cleaner than coal or oil by many. This means that whilst it is highly useful and important as a fuel source, there are still significant environmental consequences of burning oil and gas.
The supplies of coal remaining in the world are estimated to be approximately 100 years, but supplies of oil are thought to potentially last just another 20 years unless significant quantities are found elsewhere, possibly in environmentally-sensitive areas for wildlife such as Antarctica.
The extraction and transportation of oil and gas can result in large-scale and devastating environmental accidents if something goes wrong. The most common issues regarding oil are from oil spills into the sea either from damaged tanker ships which are transporting it or from damage to undersea wells. As well as creatures living in the sea, the oil slicks can wash up onto the beach, affecting birds and other wildlife over a significant area.
The process of extracting gas can also be damaging to the environment, invasive and put people's health at risk, as this article on fracking shows.