How Do also fossil fuels differ from fossils?

Answer 1

Fossil fuels and biomass fuels have similar origins, but fossil fuels have additionally undergone extreme conditions over a long period of time and are thus more energy dense.

Microorganisms and plants fix CO2 from the atmosphere and incorporate the carbon into the organic molecules that are a part of their structure. They use energy from the sun to power this synthesis of organic material. This energy stored in carbohydrates can be released by, for example, cutting down a tree and using it as firewood to heat a house. Firewood is an example of a biomass fuel. Fossil fuels are similar to biomass in that their creation also begins with microorganisms and plants using energy from the sun to fix CO2 into carbohydrates. But there are several more steps in the creation of fossil fuels. The organisms die, are buried deep below earths crust, exposed to extreme temperatures and pressures, and converted into petroleum or coal. All of this occurs over a geologic timescale, millions of years. So today when we burn fossil fuels we are releasing the energy stored from the sun millions of years ago. Since fossil fuels have aged for so long and are exposed to such extreme conditions below earths crust, they have a much greater energy density than biomass fuels.