One of my favorite science demonstrations starts like this. I ask my audience, “How many of you were ever babies?” Most indicate that, yes, they did begin life as infants. Next I ask if they are bigger now than they were then. Again, general assent.

“How did you get that way?” I ask.

“By eating food,” is the answer I eventually get, sometimes not without a little prodding.

Next I hold up two objects. One is an acorn. The other is a tree limb. Once we establish identity and relative size, I ask, “How does this (the acorn) grow into this (the tree limb)? We eat food to grow. What does the tree eat?

Nine times out of nine point one, the adults prod their children – with the wrong answer! They say things like “soil,” or “sunlight.”

I have to be very careful here, because it’s so important to teach gently. And yet the wonder of the answer is so awe-inspiring that I have to deliver it with all the gusto it deserves. A tree, I finally reveal, is made mostly of air.*

In my book The Turtle and the Universe I discuss this amazing fact in the context of global climate change. Trees turn air (actually carbon dioxide in the air) into wood. When wood burns, that carbon dioxide returns to the air, available for the next tree to consume.

When we burn coal, we’re releasing the carbon dioxide stored up not by a single tree over its lifetime, but rather the accumulated CO2 of thousands of trees, built up layer upon layer for thousands or even millions of years. A millennia’s worth of CO2, reversed in a single afternoon.

All this CO2 can have dire effects on sea turtles. Like other turtle eggs, sea turtle eggs depend on the temperature of the sand to become either male or female. As CO2 in the atmosphere drives up temperatures, more and more sea turtles become female, fewer and fewer turn out to be male. If global temperature change results in a imbalance of males and females, sea turtle populations all over the world could come crashing down.

But, according to Dr. Blair Witherington, a sea turtle expert and author, and one of the scientists I interviewed for my book, higher temperatures could have an even more direct effect on sea turtle nests. It could cause them to disappear altogether.

Witherington worries that as temperatures rise, sea levels increase. Humans, loving beaches almost as much as sea turtles do, build expensive structures right on those beaches. As sea levels rise, we will want to protect those investments. One way to protect beachfront property is to harden the beach, building sea walls or other hard structures that keep the rising water out.

But that which keeps out seawater keeps out turtles, as well. With no beaches to lay their eggs, sea turtles, those ancient mariners of an even more ancient sea, will disappear forever.

The Turtle and the Universe is a book of evolution – evolution of stars, evolution of the elements within those stars, evolution of the planet, and the biological evolution of sea turtles and all other living things. Evolution never stops, but one certain way to end a species’ biological evolution is to drive that species to extinction. It would be a sad end for such a distinguished group of animals.

And yet life, and the universe, often find a way. The Turtle and the Universe is a celebration of what’s possible, what this amazingly creative universe has done so far, and what it may still do in the future. It just may be, as we discover in the book, that it’s “turtles all the way down.”

*OK, for those of you more detail-oriented, here’s the story of photosynthesis. Trees and other plants take in CO2 and H2O and turn these raw ingredients into sugar (C6H12O6) and oxygen (O2). The sugar goes into building the tree – leaves, branches, trunk, and roots. The oxygen is released into the air as waste.

Clearly the carbon had to come from carbon dioxide. Just as clearly, the hydrogen had to come from water. What about the oxygen? The obvious choice is that the tree just splits the carbon off the CO2, combines it with water, and voila, there you have sugar.

But that’s not how it works.

In 1941 four scientists named Ruben, Randall, Kamen and Hyde performed careful measurements using a special kind of oxygen called oxygen-18. Oxygen-18 is heavier than ordinary oxygen (called oxygen-16). By giving one set of plants oxygen-18 rich water, and giving another set oxygen-18 rich carbon dioxide, and then looking for oxygen-18 in the plant’s waste gases, the scientists showed that the oxygen given off by plants comes not from carbon dioxide, but rather from water. The absorbed carbon dioxide stays within the plant. In this way, scientists showed that the dry weight of a tree comes chiefly from carbon dioxide gas, not from water. In fact, around 93% of the tree’s dry weight is from carbon dioxide. Trees are made mostly of air!