Darwin and the age of the Earth

No, the conflict was mere socio-political.
Darwinism permit to say that the "best" are the one who rule the world.
Saying that if the "lords" are ruling over the poors, it is because they have "some merit" due to superior genetic (fitness).

Yeah no, Social Darwinism wasn't created by Darwin, nor was it a scientific theory. It was a misunderstanding of fitness as others have pointed out. Living things evolve to cooperate more often than fighting. Our very cells are proof of this.

"free-living prokaryotic ancestors of modern mitochondria permanently fused with eukaryotic cells in the distant past, evolving such that modern animals, plants, fungi, and other eukaryotes are able to respire to generate cellular energy."

A question for the biologists . . .

Received wisdom goes something like this:

Circa 1860 Darwin had just proposed his theory of natural selection to an unsuspecting world. But the big honchos of the day (Lord Kelvin et al) put a damper on the proceedings by insisting that the Earth is only 20 million years old or something.

Everyone shrugged and said "Darwin, you're fooked. Twenty millions years isn't nearly enough time for natural selection to produce the biological diversity we see before us. Go stand in the corner".

Then we found out the Earth was a lot older, all was well, and Darwin smiled for the first time in his life.

My question is: How exactly did they determine that twenty million years isn't enough?

A lot can happen in twenty million years.
Geology was still quite nascent and radiometric dating was still many decades off.
A few factors were erosion of large structures and rock formations. I would look at the earliest works of people like Lyell.
When Darwin made the huge leap to common ancestry of ALL life he reasoned that going from a to b to where we are now would take immense amounts of time. I would finger through origins to see how he puts it.