Pliocene Epoch, the geologic epoch that began about 6,000,000 years ago and lasted about 4,000,000 years. It is a subdivision of the Tertiary Period of the Cenozoic Era. Great uplifting occurred in the mountains of the northwestern United States during the Pliocene Epoch. Pliocene formations in California are sources of petroleum.
The world of famous gemstones is a strange one. If we had a nickel for every gargantuan, mystery-shrouded, supposedly cursed ruby or diamond, we'd have enough money to buy one of them.
The world of our far-future descendants may be as unrecognizable to us as our bustling, urbanized world would be to our bewildered ancient forefathers. Will energy drive many of those changes?