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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SYDNEY: All molecules are not created equal. Some have saved billions of lives, wreaked environmental havoc or made the world a more colourful place. Here's our selection of those that have changed the course of human history.

PENICILLIN — R-C₉H₁₁N₂O₄S
When British microbiologist Alexander Fleming stumbled upon penicillin in 1928, he couldn't have imagined the impact it would have on modern medicine. Fleming noticed that Petri dishes with mould on them grew no bacteria, and in doing so discovered the first antibiotic. Before penicillin came into widespread use in the 1940s, wounds and diseases like syphilis were killers; antibiotics have since saved an estimated 200 million lives.

SODIUM CHLORIDE — NaCl
Salt paved the way for modern civilisation; it was used to preserve vegetables and meat as long as 4,000 years ago. This gave our ancestors the freedom to store food for hard times, travel long distances and live in harsh climates. Salt is also an important ingredient in the production of chemicals, soap and paper. Sodium chloride is in such high demand that in 2006 alone, 240 million tonnes were produced.

POTASSIUM NITRATE — KNO₃
As the key ingredient in gunpowder, potassium nitrate allowed humans to propel bullets from guns and, in doing so, changed the face of warfare. Today, there are more than 500 million handguns in circulation, causing at least 1,000 deaths every day. The formula for gunpowder was likely discovered in the 8th century, although it wasn't until the 13th century that it was first used in canons.

ASPIRIN — C₉H₈O₄
Aspirin is the most widely used drug in the world, with more than 100 billion tablets consumed annually. The active component, salicylic acid, originally from willow bark, was used as a folk remedy as long ago as the 5th century BC. But it wasn't until 1897 that German chemist Felix Hoffman managed to synthesise aspirin in a pure and stable form, making it one of the earliest synthetic drugs. Aspirin is now taken for a huge variety of afflictions, from fever and arthritis to the prevention of heart attacks, stroke and dementia.

SODIUM STEARATE — NaC₁₈H₃₅O₂
It's hard to imagine how life might have smelled for the human race prior to the invention of soap. More fastidious hygiene has also been important for stemming the spread of disease. Sodium stearate, the active ingredient in soap, works its magic by helping oil to dissolve in water. According to the United Nations Children's Fund, hand washing with soap prevents up to 1.4 million deaths per year through acute respiratory infections.

SILICON — Si
In 1954 the first silicon transistor initiated what has become a A$160 billion global market in semiconductors. Silicon is a key component of computer chips and circuits and it's estimated that there are currently more than one billion computers in use worldwide. Silicon is also used in solar cells, waterproofing treatments and seals, explosives and breast implants.