A history of killing pain: First used in the 5th century, aspirin is the most widely used drug in the world, with more than 100 billion tablets consumed annually.

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IRON — Fe
Iron accounts for at least 90 per cent of metal production. Without it we wouldn't have powerlines or oil refineries. Iron is a key component of cars, trains, planes, ships, fridges, dishwashers and computers. As a chemical it's also used in insecticides, water purification, sewage treatment and the production of ammonia. Iron was first smelted 3,500 years ago, but it wasn't until English engineer Henry Bessemer's invention in 1856 of an inexpensive way to mass-produce steel from iron that its use skyrocketed. In 2007 alone, 1,900 million tonnes of iron ore were produced, with 98 per cent of that used to make steel.

ETHANOL — C₂H₆O
If your head is swimming, you're seeing double and suddenly finding everyone attractive, chances are that ethanol is to blame. Worldwide, about two billion people enjoy ethanol, the intoxicant in alcohol. The average Australian, for example, drinks about 10 L of pure alcohol each year. Historians suspect that it was accidentally discovered when our ancestors' grain stores were drenched with rain and fermented by the Sun. The liquor reduces inhibitions, alters moods, impairs judgement and boosts sexual desire. Alcohol consumption is the third largest risk factor for disease in developed countries.

SULPHURIC ACID — H₂SO₄
A country's production of sulphuric acid is a good indication of its industrial might, because at some stage nearly every manufactured good comes into contact with this highly corrosive stuff. It's used in mining, steel production, oil refining and chemical synthesis, and in the manufacture of fertilisers, detergents and plastics. No wonder it's nicknamed "the king of chemicals". Sulphuric acid was discovered in the 8th century, but it only became economically viable in 1746, when English chemist John Roebuck developed a way to produce it in bulk. In 2005 world production of sulphuric acid was estimated at 193 million tonnes.

PROGESTIN — C₂₁H₃₀O₂
As the principal component of the pill, progestin allowed women to separate sex from procreation, giving them unprecedented freedom and control over their lives. First synthesised in 1951 by Austrian Carl Djerassi, progestin stops ovulation by imitating the hormone progesterone. Between 1965 and 1995 global fertility rates fell from 4.9 to 2.8 children per woman, largely due to the pill. Today, more than 70 million women around the world use this oral contraceptive.

CARBON DIOXIDE — CO₂
Scottish chemist Joseph Black discovered and isolated this potent greenhouse gas in the 1750s. At that time, man-made CO₂ emissions were about three million tonnes per year. But by 2005, emissions from fossil fuels alone were 7.9 billion tonnes, with another 1.5 billion tonnes caused by forest clearing. Carbon dioxide is the second most important greenhouse gas (after water vapour), trapping heat in our atmosphere and increasing global temperatures via the greenhouse effect. Emissions continue to climb, so unless there's a drastic turnaround, expect the sea level rises, extreme weather events and mass extinctions associated with a rapidly warming globe.