Made almost exclusively by living things, limestone is born in water and dissolves in it. It raises cliffs and atolls, gives cities their colour, keeps in its caves the traces of our ancestors. To follow it around the world is to understand that we live in what invisible beings left behind them when they died.
The limestone of Étretat formed 100 to 80 million years ago, in an ocean some 300 metres deep, a paradise for coccolithophores.Off Étretat, aboard the vessel Tara, the marine microbiologist Colomban de Vargas hauls in his net. A litre of seawater contains between ten and a hundred billion planktonic organisms, the basis of all life in the ocean. Among them, coccolithophores have learned to make small plates of limestone inside their cell. When they die, they fall to the bottom. For 20 million years, in the age of the dinosaurs, two centimetres build up every thousand years, and these mountains born underwater end up exposed when the English Channel opens. Beings made of a single cell thus change the chemistry of the Earth and its morphology. Today we burn what they buried, for oil, the researcher points out, comes mostly from these muds: “our whole economy is based on plankton graveyards”.
Having appeared nearly a billion years ago, coccolithophores today make more than half of the planet’s limestone.In Namibia, the geomorphologist Grégory Dandurand searches for the fissures that lead to caves. They trap what falls in from outside and preserve hominid remains three or four million years old. Australopithecus, more often prey than predator, sometimes ends up there. But the rock face recedes, the traces fade, and limestone becomes for him “the memory of the Earth, which is disappearing little by little”. Beneath Paris, the geologist Geoffroy Mesnier walks the tunnels dug by the quarrymen and reads the rock beds like the pages of a book, back to a tropical sea 44 million years old. The stone brought up from there gives the capital its hue and its identity. In Dover, the ecologist Melanie Wrigley, who grew up amid the white of the chalk, thinks that the nature of the rock we live on can affect our personality.
Notre-Dame, the Sacré-Cœur, the foundations of the Eiffel Tower: beneath Paris, 300 kilometres of tunnels bear witness to the extraction of limestone.
In the late 18th century and in the 19th, nearly 3,000 quarrymen worked at the same time beneath the south of Paris, without explosives, horses or electricity.Limestone provides a living, and it grinds people down. In Al-Minya, in Egypt, Ali Ahmed has been cutting it since 1985 for 30 euro cents an hour, with no other means of earning a living. In Dover, scarcity creates abundance: chalk lets the rain drain away, plants compete, and up to 50 species can be counted in a square metre. On Vancouver Island, Paul Griffiths and Carol Ramsay have spent almost 50 years studying this hidden world which pollutants from the surface enter without difficulty and which stands, says the karst scientist, “at the heart of the cycle of life”. In the Florida Keys, the acidification of the waters is beginning to dissolve what coral has built. The biologist Jessica Levy replants, with seven nurseries, a small hammer and glue. We walk on the work of tiny lives, and it now depends on us whether they can carry it on.
Dust, sun, blades: in the 300 or so open-cast quarries of Al-Minya, “those who have lost an arm or a leg are past counting”.
A very pure limestone, made of microscopic shells, chalk rarely outcrops at the surface of the globe: in England, in France and in a few other places in Europe.Limestone is the fruit of life, and its founder.