James Hutton · Deep time
How old are the mountains?
That time, that place
Hutton trained in medicine but spent his life farming in Scotland. Plowing fields and cutting drainage, he watched for years how ground wears down and builds up.
Why this question
A simple accounting held him. Land is worn away by weather and carried down rivers to the sea. Keep that up and everything must eventually flatten.
Yet the mountains are still there. So there must be a process that raises as well as one that wears.
What was found
On the shore at Siccar Point he saw the decisive thing.
Layers standing almost vertical, with horizontal layers lying across them. Read by Steno's rules, an order follows: laid down flat and hardened, then tilted upright as a whole, then worn for a long age while standing, then buried under new layers, then lifted again.
How long does that sequence take? The age of the Earth, reckoned then from biblical genealogy, was six thousand years. Six thousand years is nowhere near enough.
He wrote that he found no vestige of a beginning and no prospect of an end.
The Earth was some six thousand years old
Horizontal strata lying across vertical ones at Siccar Point
On the time geology opened first, Darwin would later think about how life changes