Undeniable (5 page)

It's not too hard to imagine a corporation, given countless years, with the ability to fire every employee that was not as good as another one. Eventually, after millions of employees came and went, the company would be the best in the world at doing whatever it did. Boeing actually has employed over a million different people since it was founded almost a century ago, but Boeing has not had nearly as much time to work things out as nature has. Nevertheless, we see both bottom-up and top-down processes at work. Airplane designs have been tried and discarded, just like bottom-up evolution, and the end solution looks (not surprisingly) similar to the one that emerged from evolution. But the airplane designs were created
de novo
(from new) by human brains in a distinctly human, top-down organization.

We are at once constrained to play the hand that creation deals us, and empowered to come up with our own top-down methods to create our world the way we want it to be. We can employ our evolution-given brains to fly in planes and use our imagination to soar in spirit. We are a result of evolution, and therefore so are our creations—both the not-so-good and very good. It's glorious.

 

5

A DEEP DIVE INTO DEEP TIME

The idea that just leaving the world alone for a really, really, really long time can lead to all the different kinds of life we see seems incredible, at least until you appreciate the enormous timescale of evolution. Since the late eighteenth century, scientists have used the term “deep time” to describe the magnitude of the scales involved. Understanding just how deep the deep past really is has been likened to staring into an abyss. It's too deep to see the bottom, too deep to imagine. It can overwhelm your thoughts. But once you embrace such depths, the mechanisms of evolution begin to make sense.

The events that led from the first living cell to you and me have required a nearly unimaginable period of time. When we're talking about evolution, the expression “a long time” is an understatement. For me, here's a case in which it is an understatement to even use the expression “an understatement.” Earth is currently reckoned to be 4.54 billion years old. Based on fossilized mats or layers of bacteria, we figure life got started here at least 3.5 billion years ago.

These dates have been determined through extraordinary insight and diligence by astronomers, biologists, chemists, geologists, and geochemists. I remember very well sitting in a meeting with my beloved senior colleague Bruce Murray, who exerted great influence over the whole American planetary exploration program. At this meeting, I remarked that a certain researcher in Europe was a geologist and should have insights into some of the business we were discussing. Bruce slapped his open hand on the tabletop demanding attention. He yelled at me, “That man is no geologist! He's a geochemist!” Wow,
excuse me
, Bruce. I must have grown up in some remote illiterate part of the world, where we do or did not make the distinction.

As usual, though, Bruce made a good point. Geochemists do a lot of the most important work in reckoning the age of ancient rocks … and if we don't appreciate what they do, we are missing out on a vital part of Earth's story. It's just a little over a century since the French physicist Henri Becquerel discovered radioactivity, and with it the key to unlocking deep time. Since then, physicists have developed extraordinarily successful models of the behavior of atoms. Atoms are made of protons, neutrons, and electrons. Protons and neutrons are, in turn, made of quarks. Energy can come and go, carried by photons and neutrinos, and so on. By studying certain elements carefully, we have observed that, for example, radioactive Rubidium-87, containing 37 protons (and 50 neutrons), can change or decay to strontium, which has 38 protons. These two elements can be thought of as a radiochemical system.

When rocks are liquid or nearly liquid, what geologists call plastic, they contain a certain amount of rubidium and a certain amount of strontium. The mixture is measurable by diligent radiochemists. When that molten rock spews out of a volcano, say, it solidifies. By looking at the ratios of certain elements frozen in with rubidium and strontium, radiochemists and geochemists can determine how long ago the melt, as it's called, turned solid. In the case of rubidium and strontium, we can count on precisely half of the rubidium-87 to transmute to strontium-87 (now with 49 protons) in 48.8 billion years. That's right, almost 50 billion (with a b) years. It is the nature of radioactivity. You cannot determine what any one atom will do, but you can determine with just crazy precision how long it will take a sample of half the stuff to change from one to the other. This is where the expression half-life comes from. Furthermore, we can determine when a quarter of it will change, when an eighth of it will change, a sixteenth, a thirty-second, a sixty-forth, a one-hundred-twenty-eighth, a two-hundred-fifty-sixth, etc.

The word
chemistry
is the key in this business of geochemistry and radiochemistry. Rocks in Earth's crust typically contain a certain amount of rubidium and a certain amount of strontium, along with other elements like calcium and potassium. The chemical behavior of rubidium is a lot like the chemical behavior of potassium, and the chemical behavior of strontium is a lot like the chemical behavior of calcium. (In chemistry we see that they reside in the same columns on the periodic table of the elements.) When the rocks are liquid, rubidium tends to remain free and unattached, but as the rock cools, rubidium sometimes takes the place of potassium in the rock crystals. In the same way, strontium substitutes for calcium. So by closely examining crystals that we know contain potassium and comparing the relative abundances of rubidium and strontium that are also in the crystal, we can determine the age of the rocks relative to other rocks. We can work our way into the past, pulling our date reckoning back in time by our bootstraps.

There are several other geochemical clocks that radiochemists use to reckon the age of Earth, besides rubidium-strontium. There's uranium-lead, there's potassium-argon, and there's samarium-neodymium. Each clock reckons time using different chemical elements and each provides us with incontrovertible evidence of Earth's age. You may have heard of carbon dating or carbon-14 dating. That is a related technique that is well suited to measuring shorter timescales. It lets us work backward in time to determine when a living thing stopped transpiring (plants) or stopped breathing (animals). Carbon dating only goes back a few tens of thousands of years, because the half-life of this type of carbon is only 5,730 years. Compare that with rubidium-strontium; this radiochemical clock goes back into the past almost a million times further. Carbon dating is important for studying human history, but it's not well suited to reckoning deep time.

Evolution snaps into focus when you realize how fantastically old our planet is. To imagine it, try this. Look at a map of North America. To readers from other parts of the world, it's interesting to note that what we often call the continental U.S. extends from the Atlantic to the Pacific oceans (as do Canada and Mexico). By means of the U.S. Interstate Highway System, one can drive a car from coast to coast. If we were to go from around San Diego on the Southwestern shore of the U.S. to, let's say, Boston on the Northeastern shore, we would go about 4,500 kilometers or 2,800 miles. That much driving would take you from Lisbon, Portugal to Moscow, Russia. And along the way, you would have passed through eight different countries.

Imagine a time line running from coast to coast. Let's say that for every kilometer of travel (every ten football fields for U.S. readers), you pass through one million years of time. Well then, every meter (about every yard) represents one thousand years of time. For this charming thought-model, the distance from your chin to your outstretched arm represents a thousand years. A Thousand Years!

For the next step, imagine yourself walking through time from San Diego to Boston. When you start, Earth is still a big orange-hot ball of molten rock. After two hundred kilometers, six or seven days into your hike, look up as you come across a marker reminding you that the Moon is forming. Another two days of walking, and a marker tells you that enough rain has fallen on a surface cool enough to have the ocean form; that was 4.4 billion years ago. After a month on foot, you'll be coming upon the first signs of life, about 3.5 billion years ago. Two thousand kilometers from your embarkation point, somewhere near Broken Arrow, Oklahoma, you'll find tiny microbes, blue-green bacteria. Before that, by the way, you would have suffocated along your route, because there was no significant amount of oxygen in the air. Earth's oxygen was a byproduct of photosynthesis in those early microbes. The blue-green bacteria, along with you and me, are the only single species known to be capable of altering the climate of an entire planet.

Two months into your trek, perhaps not too far from Little Rock, Arkansas, the ancient supercontinent of Rodinia has formed. Another month on the road, and you may notice that a more recent ancient supercontinent, Pangaea, has formed. Not all, but almost all of the living things you encounter are in the ocean. Wait, you wouldn't encounter them, unless you were walking when most of the current interior of the United States was under water, under an ancient inland sea. As you slog forward, unusual and by our standards bizarre sea creatures abound.

When you're only 230 kilometers (120 miles) from the eastern shore, you finally come upon the ancient dinosaurs. They are latecomers in the long history of life. You walk in their midst for 100 kilometers. That would be two or three days at a good pace. Along the way, plants that produce flowers appear. Sex is everywhere now.

Just two kilometers to go now, and the Atlantic Ocean might be in view. And here, you meet the first of us—early versions of humans, living just 2 million years ago. Keep on; you might meet some of our cave-dwelling ancestors. Within five meters of the water's edge, the ancient pyramids appear. Now, within twenty centimeters, not even the distance from your pinky fingertip to the end of your thumb, the United States as a nation comes to be. The human landing on the Moon is just two centimeters, less than an inch, from the water. Press your toes forward and you arrive at today.

Now turn around. Look back across the vastness of the continent. Most of it looked barren or desolate on your trek. All that we know of history, all the people and their affairs, everything you've come to know, takes place in less than your last stride. It's this vastness of time that has enabled life to begin and evolution to direct the creation of all the living things we've ever known.

Notice that during about three quarters of your hike, living things were just revving up. There were bacteria, lots of them. But the plants that you and I eat, along with the animals we raise for food and fertilizer, all came to be when you had almost completed your journey. Most of life's time here on Earth has been spent making the slow evolution from a few crudely self-copying chemicals to the first true cells to relatively uncomplicated, but nevertheless remarkable, living things. It is only very recently in the deep timescale of things that complicated animals like you, me, and my bewitching old girlfriend came to be.

When Charles Darwin and Alfred Wallace were pondering the consequences of their discoveries, they were deeply troubled by what seemed to be the tremendous amount of time required to get life to where it is now, or where it was when they lived. Darwin published
On the Origin of Species
in 1859. Radioactivity wasn't even discovered until 1896, and wasn't well understood until many years after that. So even as Darwin developed his elegant theory, which he established through dozens of remarkable, diligently executed clever experiments, he was constrained by a lack of a reasonable explanation for how evolution could have enough time to act. He couldn't explain how Earth could be so fantastically old.

Darwin's contemporaries challenged him, even ridiculed him, for asserting that all the living things we've ever seen on Earth have a common ancestor and came into existence over this vast expanse of time. How could it be? How could that much time have passed? It is still unimaginable for most of us, let alone to people in Darwin's day.

Through the late-nineteenth century, William Thompson (who was Irish but went by the uniquely British sobriquet of Lord Kelvin) provided the science world with a seemingly authoritative calculation that Earth was between 20 million and 400 million years old, tops. Evolution seemed to require ten or a hundred times as much history. It was a paradox. The true age of Earth remained a mystery through Wallace's and Darwin's lives. It wasn't until the discovery of radioactivity that scientists grasped the answer. Kelvin had assumed that Earth had been cooling ever since its birth, and he used its present temperature to deduce its age. What he didn't know is that radioactive elements deep inside our planet keep adding new heat. His calculations were perfect, but his understanding was not. In fact, there was plenty of time for evolution to unfold—every bit as much as Darwin imagined, and then some.