It's about 7,000 years ago and we're looking for a shallow place, just off the coast, where an amazing variety of beautiful shells existed.

Although plenty of sharks still hunt these waters, the really big one, Carcharodon megalodon, has already gone extinct. But it's still a good idea to be careful.

(right) This beautiful shell is called Vassum horridum. If it had a color, it faded long ago. No one has ever seen a living one. To me, it's a marvel of shape.

Those spines were designed to keep other snails from drilling a hole into the shell and eating it. As you can see, it didn't work. A snail climbed on this shell's back and drilled that hole in its center. But this vasum does the same thing to other shellfish.

And, that's what seashells are all about. Their wonderful shells are body armor for the creatures that live inside them.

Left) This Crown conch lived at the same time. The Vasum above went extinct, but Crown conchs still survive in the estuaries of modern Florida. How that works remains an unanswered question.

Like life on land, the animals beneath the sea live in very distinct environmental systems. You can look at it from the ocean to the land, or from the land to the ocean. The path goes either way and is wonderfully exciting.

When you jump into the ocean with your snorkle and fins, the images at first are a confusion of sights. It's like landing in the middle of an unknown forest. What you usually see is the single environmental system which surrounds you.