DaVinci believed that "Alpine peaks were once the floors of seas"

"Few art historians doubt that Leonardo’s vision was influenced by his memory of a mountain excursion on which he found himself wandering “among gloomy rocks”. “I came to the mouth of a great cavern... discovery inside of a fossilised whale and a horde of ancient seashells whose engrossing geometric grooves he would memorialise in the pages of his notebooks...

Over the ensuing years, the perplexing presence of “oysters and corals and various other shells and sea snails” on “the high summits of mountains”, far from the sea, worried away at the artist’s imagination. For Leonardo, the accepted explanation by ecclesiastical scholars of a great flood, such as that described in the Old Testament, for the relocation of these shells, didn’t wash. These creatures weren’t thrown there. They were born there.

Seashells in mountains were proof, Leonardo came to believe and confided to his journal, that Alpine peaks were once the floors of seas. And the Earth was therefore much older and far more haphazardly fashioned by violent cataclysms and seismic upheavals over a vast stretch of time (not the smooth hand of God in a handful of days) than the Church was willing to admit...

Continue reading at the BBC, where there is discussion of this worldview in relation to the iconography he inserts in his paintings.