Of all building materials ever invented, the most versatile would probably be concrete. It's cheap, strong and can be formed into almost any shape.
It's also one of the oldest, with the earliest known use in the remarkable Uxmal Mayan 'pyramid'. There are also examples in Syria and northern Jordan dating to the 4th century BC.
The stunning Pantheon in Rome, still standing after nearly 2000 years, is testimony to its strength and durability.
Concrete begins with a sedimentary rock such as limestone which usually forms in shallow marine waters from organisms that use calcium carbonate to make shells, skeletons and coral.
This and other ingredients are mined and transported to a cement factory.
The finely ground raw material including iron ore or fly ash is fed into huge cylindrical steel bins.
These sit inside kilns that might be as high as a 40-storey building.
The kiln is heated to around 1480 degrees Celsius. Fuels such as powdered coal, oil or gas produce a roaring blast of flame to drive off gasses including CO2.
Clinker is extracted as grey balls, about the size of marbles. Ground and mixed with gypsum and limestone, it makes cement. Cement is then mixed with aggregate to make concrete.
Much of the limestone originates from the Carboniferous Period, between 363 and 325 million years ago, making it comparable to coal.
Both contain fossil carbon and their use is releasing enormous quantities of CO2.
Cement now contributes about 8 per cent of global CO2 emissions and, if concrete were a country, it'd be the third-largest polluter.
While electrification of kilns to replace coal or gas is being investigated, it is not currently technically or economically viable.
Some improvements are possible however, such as using waste materials as energy sources rather than fossil fuels.
Another hope is a technology being developed to inject CO2 into concrete where it will be captured instead of being emitted.
Concrete has been found to reabsorb some CO2 during its lifetime through the process of carbonation. Unfortunately that can lead to the corrosion of steel reinforcing and so-called concrete cancer.
While improvements in concrete production may be possible, they are nowhere near enough to offset growing population and urbanisation.
As long as world population continues to increase, so will our use of concrete and, with it, CO2 pollution.
Nowhere is this more apparent than in China, which used more cement between 2011 and 2013 than the US did in the entire 20th Century.
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