[cmrdporcupine]

If you take a core sample from an established forest it's often got at least 5-6 feet of heavy dark carbon rich soil beneath. That's the case on my property anyways. I had some trees moved with a giant tree spade some years back. Sandy soil, but the top 5 feet was nice and dark. The area would have been forest and marsh only about 50-100 years ago.

[DenisM]

Amazon has been around for 55 million years. Do you think we will find the topsoil to be 55,000,000 / 100 * 5 feet thick? I wager it went up to like 20 feet max in the first million years and hasn’t changed since then.