A fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organisms, containing energy originating in ancient photosynthesis. Such organisms and their resulting fossil fuels have an age of millions of years, sometimes more than 650 million years. Fossil fuels contain high percentages of carbon and include petroleum and natural gas. Used derivatives of fossil fuels include kerosene and propane. Fossil fuels range from volatile materials with low carbon-to-hydrogen ratios, to liquids, to nonvolatile materials composed of pure carbon, like anthracite coal. Methane can be found in hydrocarbon fields either alone, associated with oil, or in the form of methane clathrates; as of 2018, the world's primary energy sources consisted of petroleum, natural gas, amounting to an 85% share for fossil fuels in primary energy-consumption in the world. Non-fossil sources included nuclear and other renewables. According to another source, world renewable energy-consumption was 18% in 2018.

When compared with the previous year, world energy-consumption grew at a rate of 2.9% double its 10-year average of 1.5% per year, the fastest since 2010. Although natural processes continually form fossil fuels, such fuels are classified as non-renewable resources because they take millions of years to form and the known viable reserves are being depleted much faster than new ones are being made. Most air pollution deaths are due to fossil fuels, fossil fuel phase-out would save 3.6 million lives each year. The use of fossil fuels raises serious environmental concerns; the burning of fossil fuels produces around 21.3 billion tonnes of carbon dioxide per year. It is estimated that natural processes can only absorb about half of that amount, so there is a net increase of 10.65 billion tonnes of atmospheric carbon dioxide per year. Carbon dioxide is a greenhouse gas that increases radiative forcing and contributes to global warming along with ocean acidification. A global movement towards the generation of low-carbon renewable energy is underway to help reduce global greenhouse-gas emissions.

The theory that fossil fuels formed from the fossilized remains of dead plants by exposure to heat and pressure in the Earth's crust over millions of years was first introduced by Andreas Libavius "in his 1597 Alchemia " and by Mikhail Lomonosov "as early as 1757 and by 1763". The first use of the term "fossil fuel" occurs in the work of the German chemist Caspar Neumann, in English translation in 1759; the Oxford English Dictionary notes that in the phrase "fossil fuel" the adjective "fossil" means "btained by digging. Aquatic phytoplankton and zooplankton that died and sedimented in large quantities under anoxic conditions millions of years ago began forming petroleum and natural gas as a result of anaerobic decomposition. Over geological time this organic matter, mixed with mud, became buried under further heavy layers of inorganic sediment; the resulting high levels of heat and pressure caused the organic matter to chemically alter, first into a waxy material known as kerogen, found in oil shales, with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis.

Despite these heat driven transformations, the embedded energy is still photosynthetic in origin. Terrestrial plants, on the other hand, tended to form methane. Many of the coal fields date to the Carboniferous period of Earth's history. Terrestrial plants form type III kerogen, a source of natural gas. There is a wide range of organic, or hydrocarbon, compounds in any given fuel mixture; the specific mixture of hydrocarbons gives a fuel its characteristic properties, such as boiling point, melting point, viscosity, etc. Some fuels like natural gas, for instance, contain only low boiling, gaseous components. Others such as gasoline or diesel contain much higher boiling components. Fossil fuels are of great importance because they can be burned, producing significant amounts of energy per unit mass; the use of coal as a fuel predates recorded history. Coal was used to run furnaces for the melting of metal ore. Semi-solid hydrocarbons from seeps were burned in ancient times, but these materials were used for waterproofing and embalming.

Commercial exploitation of petroleum began in the 19th century to replace oils from animal sources for use in oil lamps. Natural gas, once flared-off as an unneeded byproduct of petroleum production, is now considered a valuable resource. Natural gas deposits are the main source of the element helium. Heavy crude oil, much more viscous than conventional crude oil, oil sands, where bitumen is found mixed with sand and clay, began to become more important as sources of fossil fuel as of the early 2000s. Oil shale and similar materials are sedimentary rocks containing kerogen, a complex mixture of high-molecular weight organic compounds, which yield synthetic crude oil when heated. With additional processing, they can be employed in lieu of other established fossil fuel deposits. More there has been disinvestment from exploitation of such resources due to their high carbon cost, relative to more processed reserves. Prior to the latter half of the 18th century and watermills provided the energy needed f

John Clark is an Australian former rower. He was a six-time national champion who competed at world championships and in the men's eight event at the 1972 Summer Olympics. Clark's senior rowing was from the Mosman Rowing Club. In Mosman crews he contested both the coxed and the coxless four events at the 1970 Australian Rowing Championships and he won the national title in the coxless four, he won both the national coxed pair and the coxless four titles in Mosman crews in 1975 and in 1976 he again contested both the coxed and the coxless four events and won the coxless four national championship. He first made state selection for New South Wales in the men's eight which contested and won the 1968 King's Cup at the annual Interstate Regatta, he raced in further New South Wales King's Cup crews in 1969, 1971 and 1972 and saw a second victory in 1972. The entire New South Wales winning King's Cup eight of 1972 was selected as the Australian eight to compete at the 1972 Munich Olympics. Clark rowed in the six seat of that boat.

In 1975 as the Australian champion coxed pair Clark, Michael Crowley and coxswain Terry O'Hanlon were selected to race Australia's coxed pair at the 1975 World Rowing Championships in Nottingham. They were eliminated in the repechage. A high-school history and science teacher Clark taught and coached schoolboy rowing at St Joseph's College, Hunters Hill and the Shore School in the 1970s and 1980s. John Clark at FISA WorldRowing.com

The Aarhus Letbane is a light rail system in the city of Aarhus, Denmark. It is operated by the company Midttrafik; the first line opened in December 2017, but the system is under continuous development and expansion. Service on the intercity section Odder to Lisbjergskolen opened on August 25, 2018. A third intercity line to Grenå opened on 30 April 2019. More lines are being planned. On 8 May 2012, the Danish Parliament approved the construction of the first line, it was planned to open in August 2016, but this was delayed, in part due to legislative issues in relation to railway safety. Two types of rolling stock have been operated over the first line, conventional trams which are slower and restricted to only running along some parts of the route and hybrid tram-trains that can be operated on the conventional heavy rail network, the latter being used for the long distance services; the Aarhus Letbane is the only operational light rail system in Denmark. Light rail systems are under construction in both Odense and Greater Copenhagen.

The development of a light rail system around Aarhus, the second biggest city in Denmark, was proposed as early as 2006. In response to rising interest in the concept, during January 2009, the Danish Parliament granted an allocation of DKK500 million to support the light rail project as part of a wider green transport package. During October 2010, work commenced upon several studies. According to transport authority Midttrafik, who operated the completed network, the Aarhus light rail programme had drawn considerable inspiration from tram-train operations on the tram network in Kassel, Germany. In addition, consultancy firms COWI A/S and SYSTRA contributed their own studies and technical support for the project, including an initial feasibility study and development of tender documentation; the project's Environmental Impact Assessment report was produced by C. F. Moller. Various different approaches for the network were being considered at one stage, including the full electrification of the route, the procurement of a combination of 750 V DC trams and electro-diesel tram-trains.

It was recognised that, if the option of full electrification was to be exercised, a catenary-free system may be chosen for the harbour-side element of Phase 1. By late 2012, it had been decided that Germany's BOStrab light rail regulations would be applied to the tentative network, while Lloyd's Register was appointed to serve as the independent safety assessor. By mid-2012, construction activity was scheduled to begin during June 2013, while the light rail network's opening was planned to occur during August 2016. On 8 May 2012, the Danish Parliament gave its approval for the construction of the Aarhus light rail line, which would be the first such modern line in Denmark, granted the legal powers to proceed with the initiative; as a consequence, the Aarhus Letbane joint venture between the local municipality, the Ministry of Transport and the Midtjylland region was formally established to promote and further the project during August 2012. The construction of Phase 1 has been estimated to have cost DKK 2.4 billion.

Additionally, the European Investment Bank provided DKK14.2 million to the initiative as part of the European Commission’s European Local Energy Assistance programme. The competitive tendering process for the network's construction was launched shortly after the formation of the joint venture; the contracts for the construction of Aarhus light rail line were awarded in three separate packages. During July 2014, a German-Italian consortium, comprising Stadler Rail and Ansaldo STS, was awarded the contract for the construction and outfitting of Phase 1 of the Aarhus light rail. Stadler supplied the rolling stock for the line while Ansaldo STS provided the associated infrastructure, such as the tracks, signalling systems, control centre, maintenance facility. Phase 1 is a 12 km double-track tramway running from Aarhus H station, via Skejby and Lisbjerg to Lystrup; the line forms a loop spanning across Aarhus' city centre, linking into the existing regional railways running to Odder in the south and Grenaa in the northeast.

The two existing local lines have been electrified and adapted in other ways to Phase 1, but these alterations have not involved any change to their alignment. Furthermore, the heavy rail station at Aarhus, along with existing park and ride facilities near major stops along the route have been refurbished. Various pieces of infrastructure and civil works were performed during the construction phase of the project. During October 2014, work commenced on the boring of a pair of tunnels to carry the tramway between Aarhus University and Aarhus University Hospital in Nørrebrogade. In the following year, both the Randers Way and Nørrebro Street had to be reduced in width in order to allocate space between the lanes for the installation of the new double-track line. In total, eight bridges had to be constructed during Phase 1.