Pprofessor emeritus of natural history at Harvard University, in the United States, Andrew Knoll is a leading authority in his field, the history of the Earth. He roamed Siberia, the Arctic island of Spitsbergen and the desert expanses of Western Australia in the hunt for fossils and ancient rocks. With the idea, unusual at the start of his career, that the physical Earth and the biological Earth form a stormy but forever united couple.
Rocks, volcanoes, mountains, climate, ocean chemistry and atmospheric chemistry are closely linked to the convulsions of life. “The Earth is not a simple passive platform hosting population dynamics. Its environments evolve, whether on local and transient scales or on global and sustainable scales,” underlines the author.
Without plate tectonics, this permanent sliding of shreds of the earth’s crust, no permanent volcanism, no cycle of carbon buried underground then released again on the surface, and no life in the sense in which we understand it. More than 700 million years ago, “Snowball Earth” escaped complete and eternal glaciation thanks to volcanoes that continued to disperse carbon dioxide into the atmosphere. It boosted the greenhouse effect and warming which destroyed the ice.
And despite everything, life
Despite these permanent shocks, or rather because of them, the cards of life have been constantly redistributed with ecosystems very different from each other millions of years apart. The Earth, assembled more than 4.5 billion years ago, was already home to primitive life some 500 million years later. For half of its history, neither its atmosphere nor its oceans housed the slightest molecule of oxygen. And yet bacteria and archaea – another form of microorganisms – thrived.
For half of its history, neither its atmosphere nor its oceans housed the slightest molecule of oxygen
Then came a major crisis, the Great Oxidation which started 2.4 billion years ago and which finally breathed oxygen into the system. “Cyanobacteria were the heroes of this revolution,” suggests Andrew Knoll. The living organisms which colonize the land, the development of animal life – which occupies the last 15% of the timeline –, the Cambrian explosion 541 million years ago, the five great extinctions, the appearance of hominins who have stood on their two legs for 7 million years: these major stages have always been the result of the harsh interaction of fauna and flora with their environment.
Homo sapiens, the final product of the lineage, is now the architect of a new extinction. Will it be “mass”? What do the previous ones have in common? “It’s their speed. The pace of environmental change is as important to consider as its magnitude,” warns the author. Looks like we tick all the boxes.
“A Brief History of the Earth” by Andrew H. Knoll, ed. The Links that Free, 264 p., €22.50, ebook, €16.99.
