Leclerc was a French naturalist, biologist, astronomer, and writer. An attorney by trade, he speculated about the origin of life on Earth and the planet’s history. His ideas were even more daring than those of his contemporary Maillet, thanks to his background in mathematics and his admiration of Newton.

A nature historian, he wrote Natural History, General and Particular, with a description of the King’s Cabinet, an encyclopedic collection of 36 large volumes. He helped establish the botanical gardens of Paris, the Jardin des Plantes. His theory, compared to Maillet’s, focused on the creation of the Earth and not the origin of life. He suggested that the planets had initially been fragments of the Sun. When a comet struck the latter, the planets broke off and began to spin around it, all on the same plane.

He also calculated that the Earth must have taken 75,000 years to cool off. He divided this span into seven different eras, setting the origin of life by spontaneous generation in the third era, the origin of the animals in the 5th, and the appearance of human beings in the 7th. He argued that lions and tigers descended from ancient cats and suggested that if conditions were to change, they would return to their original state.

Unfortunately, the Church systematically attacked his ideas and forced him to retract his theories. It was nonetheless widely known that he continued to believe what he had initially proposed.