Contains the full lesson along with a supporting toolkit, including teachers’ notes.
A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. The majority of hydrocarbons found naturally occur in crude oil (petroleum), where decomposed organic matter provides an abundance of carbon and hydrogen which, when bonded, can catenate to form seemingly limitless chains. Hydrocarbons can be gases (e.g. methane and propane), liquids (e.g. hexane and benzene), waxes or low melting solids (e.g. paraffin wax and naphthalene) or polymers (e.g. polyethylene, polypropylene and polystyrene). They can be saturated (alkanes) having no double or triple bonds or unsaturated with double (alkenes) or triple (alkynes) bonds between some of the carbon atoms. Most petroleum fuels are saturated hydrocarbons.
Countless micro-organisms live in the upper layers of the ocean, including algae, such as diatoms, and zooplankton such as copepods and other small crustaceans. When these organisms die their remains accumulate on the ocean floor along with those of other marine organisms. In this anoxic environment the organic matter decomposes and new polymers are formed and eventually become kerogen. Under the right conditions planktonic kerogen leads to the formation of petroleum, which may or may not be recoverable.
A sedimentary basin is any geological feature exhibiting subsidence and consequent infilling by a process known as sedimentation. Sedimentation causes mineral and/or organic particles to settle and accumulate, or minerals to precipitate from solution. With time (millions of years) and pressure (increased burial depths), organic matter within these sediments lead to the formation of hydrocarbons in the form of oil and gas.