 In 1027, the Persian naturalist, Ibn Sina (known as "Avicenna" in Europe), proposed an explanation of how the stoniness of fossils was caused in "The Book of Healing".He modified an idea of Aristotle's, which explained it in terms of vaporous exhalations.Ibn Sina modified this into the theory of petrifying fluids ("succus lapidificatus"), which was elaborated on by Albert of Saxony in the 14th century and was accepted in some form by most naturalists by the 16th century.