Physical Geography
The Earth as a Living Body
The water wears away the mountains and fills up the valleys, and if it had the power it would reduce the earth to a perfect sphere.
— Leonardo da Vinci
Overview
Leonardo's physical geography is among his most scientifically advanced work. He observed erosion, understood sedimentation, recognized fossils as the remains of once-living creatures (when most scholars considered them "sports of nature"), and — most daringly — challenged the biblical flood narrative using physical evidence and logical reasoning.
His vision of the earth was profoundly modern: a dynamic system shaped by water over immense periods of time, where mountains are worn down and valleys filled up in an endless cycle of destruction and renewal. He saw the earth not as a static creation but as a body in perpetual transformation — and he drew the parallel between geological processes and human physiology explicitly.
Of the Sea Which Girdles the Earth
Leonardo's geological history
I perceive that the surface of the earth was from of old entirely filled up and covered over in its level plains by the salt waters, and that the mountains, the bones of the earth, with their wide bases, penetrated and towered up amid the air, covered over and clad with much high-lying soil. Subsequently the incessant rains have caused the rivers to increase and by repeated washing have stripped bare part of the lofty summits of these mountains, leaving the site of the earth, so that the rock finds itself exposed to the air, and the earth has departed from these places. And the earth from off the slopes and the lofty summits of the mountains has already descended to their bases, and has raised the floors of the seas which encircle these bases, and caused the plain to be uncovered, and in some parts has driven away the seas from there over a great distance.
C.A. 126 v. b
"The mountains, the bones of the earth" — Leonardo's recurring analogy between the earth and the human body. What he describes here is essentially the geological principle of denudation and sediment transport: rain erodes mountains, rivers carry sediment to the sea, sea floors rise, land is created. He understood deep time before anyone had a name for it. -D
Doubt: On the Flood of Noah
Leonardo's most dangerous argument
Here a doubt arises, and that is as to whether the Flood which came in the time of Noah was universal or not, and this would seem not to have been the case for the reasons which will now be given. We have it in the Bible that the said Flood was caused by forty days and forty nights of continuous and universal rain, and that this rain rose ten cubits above the highest mountain in the world. But consequently if it had been the case that the rain was universal it would have formed in itself a covering around our globe which is spherical in shape; and a sphere has every part of its circumference equally distant from its centre, and therefore on the sphere of water finding itself in the aforesaid condition, it becomes impossible for the water on its surface to move, since water does not move of its own accord unless to descend. How then did the waters of so great a Flood depart if it is proved that they had no power of motion? If it departed, how did it move, unless it went upwards? At this point natural causes fail us, and therefore in order to resolve such a doubt we must needs either call in a miracle to our aid or else say that all this water was evaporated by the heat of the sun.
C.A. 155 r. b
Read that again carefully. Leonardo is using geometry and physics to challenge the literal truth of the Bible. If water covered the entire spherical earth uniformly, it would have no slope — and water only flows downhill. Therefore, a universal flood is physically impossible unless you invoke a miracle. He frames it as a "doubt" and leaves the door open for miracles — probably to protect himself — but the logical argument is devastating. He wrote this in the early 1500s. Galileo's trouble with the Church was still over a century away. -D
On Erosion and Deep Time
The earth transforms itself across vast ages
The water wears away the mountains and fills up the valleys, and if it had the power it would reduce the earth to a perfect sphere.
C.A. 185 v. c
The lowest parts of the world are the seas where all the rivers run. The river never ceases its movement until it reaches the sea; the sea therefore is the lowest part of the world.
Water does not move from place to place unless it is drawn by a lower position. Lowness therefore serves as a magnet for water.
C.A. 80 r. b
Make a sketch to show where the shells are at Monte Mario.
C.A. 92 v. c
"Lowness serves as a magnet for water." Leonardo personifies gravity without naming it. And the brief note about shells at Monte Mario — a hill near Rome — is a reminder that these aren't abstract speculations. He went and looked. He found marine fossils on hilltops and asked: how did they get there? His answer — that the sea once covered this land — was correct, and it took geology another 300 years to catch up. -D
Winds, Currents, and the Shaping of Shores
How rivers meet the sea
Three is the number of the winds which bend the rivers to the west as they discharge themselves into the Mediterranean Sea on the shores that face south. This is proved as follows: the sand that is driven by the winds into the water is no longer subject to the winds, through being weighed down by the water which covers it over and forms a screen for it against these winds.
Therefore the river which flows into the sea will half way in its course make a beginning of a movement to the west, when it feels the breath of the winds known as Greco, Levante and Scirocco, which at various times set the dry sand of the shore spinning, and hurl it into the sea, where it becomes submerged and settles upon the bed of the sea.
C.A. 167 v. a
This section contains some of Leonardo's bravest thinking. Questioning Noah's Flood in Renaissance Italy was not a casual intellectual exercise — it could get you in serious trouble with the Church. Leonardo did it anyway, with careful logical argument. That's the measure of the man. -D