Survival expert Bear Grylls (I've written about him here) once stood on a patch of ground in Africa and solemnly intoned, "This is the oldest place on Earth." I had to laugh: every place on Earth is the oldest place on Earth, because it's all aging at the same time.
I slapped the above thought up on Twitter, and received a "nay" from a surprising source: fellow blogger, teacher, and e-friend Brian Dean, who's much more science-minded than I am. Brian tweeted this reply:
I disagree. Some rocks have fossils 65 MY old, others are 200 MY old. Geologically some places are older.
But wouldn't you say that every molecule of the planet ages at the same rate, at the same time?
Brian wrote (squeezing as much info into 140 characters as he could):
Atoms are 1 age, molecules another and current placement another again.Uranium releases He -in lava, He gone-diff atom content
I had little choice but to concede Brian's technical point, so I said:
Sounds like a topic to blog about. I should've said "atoms."
And now I'm blogging about this topic.
Long story short: I'm not convinced that I'm wrong, and it's likely that Brian and I are talking past each other. Let me see whether I can unpack some random thoughts.
How old is the Earth? By most scientists' reckoning, the Earth is about 4.5 billion years old. When scientists posit this number as the Earth's age, they're assuming a rough starting point for the Earth's existence, i.e., the "moment" (it obviously took much longer than a moment) when the subset of matter that eventually became the Earth coalesced, becoming a proto-version of the oblate spheroid we all know and love.
But how old is the matter that makes up the Earth? That's really what I'm getting at. At a guess, I'd say that that matter is about as old as the universe itself, i.e., about 13.8 billion years old. By this reckoning, all matter is about 13.8 billion years old. We could get into the nitty-gritty of how all the wild energies a microsecond after the Big Bang weren't exactly matter yet, but that's an academic point that doesn't really bear on the discussion at hand. We could also bog ourselves down with a discussion of Einstein's rejection of absolute simultaneity (because of relativistic effects, time doesn't flow at the same rate everywhere in the universe), but that, too, would have little bearing on a discussion of Earth, which is a small enough clump of matter that we can dismiss those Einsteinian phenomena as trivially minuscule.
You could counterargue that, by claiming everything is the same age, I make it impossible to make any useful or meaningful distinctions between, say, a sapling that came into existence only a few months ago versus a 60-million-year-old plant fossil, or even between a toddler and a grandparent. But I have a guardian angel on my side: Carl Sagan famously said, in that sonorous voice of his, "We are the starstuff of the universe." What he meant, of course, is that the matter making up our bodies comes from elsewhere—from the ancient stars, and their matter ultimately came from somewhere even more ancient. The current arrangement of that matter into human forms is not ancient, but the matter itself is.
This feels almost like Madhyamaka ("Middle Way") Buddhism, a branch of religious thought that comes to us from the philosopher Nagarjuna (roughly a contemporary of Saint Irenaeus), who argued that there are "two truths," conventional and ultimate. Conventional truth is local, practical, and contextualized; ultimate truth is universal, eternal, and not dependent upon context. Conventionally speaking, I'm almost 45 years old and my brother Sean is almost 35; in ultimate terms, however, he and I are material aggregates that are nearly 13.8 billion years old. The arrangement, the pattern, that is conventionally called "Kevin" will cease to exist after, oh, twenty or thirty more orbits of our world around the sun, but the matter that belonged to Kevin will endure. So not only is every spot on Earth the oldest place on Earth, but every person, young or old, is the oldest person on Earth, too.