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therefore so are our creations—both the not-so-good and very good. It’s glorious.

 
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    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