It needs only a few hours to form. Born of the fury of volcanoes, basalt has fed legends, sheltered prehistoric people, and sometimes decided the course of History. Life may even have begun in it. And today it is basalt we are asking to take back the carbon we release into the air.
It is by cooling quickly, in contact with air or water, that lava becomes basalt, one of the most widespread rocks on Earth and one of the least visible.It all begins a few dozen kilometres down, at more than 1,200 degrees, when part of the rock melts. The most intense magmatic activity takes place at the bottom of the oceans. By drilling several kilometres into the ocean floor, researchers from the Institut de Physique du Globe de Paris have discovered microbial life there whose mass is thought to exceed that of all 8 billion humans combined. At the Saclay synchrotron, the geomicrobiologist Bénédicte Menez tracks down its signs. No light enters this basalt: seawater releases the iron and sulphur that allow living things to “endure far from the light”. On the early Earth, without a protective atmosphere, life surely drew its resources from stone in this way.
In the fractures where water has circulated, fluorescence betrays amino acids, the building blocks of proteins and a sign of microbial life.Black, the rock stores the sun and gives it back at night. Prehistoric people camped at its foot, at the Blot cliff, in the Massif Central, where Jean-Paul Raynal holds a pebble engraved with a reindeer by Homo sapiens 26 to 28 thousand years ago. Around the fire, he believes, a spiritual life was played out that “passes through stone, comes from stone and returns to stone”. On the Giant’s Causeway, in Ireland, the painter Aly Harte sees a family in the rocks. On the Namibian plateau of Etendeka, the biologist Seith Eiseb thinks of his ancestors and would talk to the rocks if he could. In the United States, in the Lava Beds, 53 Modoc warriors held off a thousand soldiers for almost six months. The archaeologist David Curtis walks there among “the ghosts of the past”.
To paint basalt, Aly Harte mixes her black from red, yellow and a little more blue, “to feel the strength, but also the beauty of basalt”.
On this plateau, Seith Eiseb’s team discovered a new species of sengi, a small shrew-like mammal that is genetically closer to the elephant.
This basalt is so sharp, explains David Curtis, that the soldiers dared not ride for fear of laming their mounts, and could not sleep.In India, the Deccan Traps flow covered 2 million square kilometres and spread its toxic gases, an accomplice in the disappearance of the dinosaurs. Today the same basalt makes the soils rich, “the backbone of all life here”, says the ecologist Aparna Watve. On the Kaas plateau, 850 plant species thrive in the micro-habitats hollowed out by erosion. But in a single week, humans release into the air as much as all the volcanoes in a year. In Iceland, around Sigurdur Gislason, carbon dioxide is dissolved in water and sent deep into the basalt, where it turns into rock in less than two years. From the carbon in us to that of plants, “everything comes from rocks”, says the geochemist. Knowing that we are made of the same matter as stone may open up another way of inhabiting the Earth.
In contact with basalt, the injected carbon dioxide turns into carbonate, a mineral: “In a way, we petrify the gas.”Basalt can take everything, but it can also give everything.