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Andrew Alden

What Is 'Deep Time'?

By August 1, 2013

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A few days ago, sedimentologist Brian Romans asked his fellow geoscientists on Twitter, "when you hear [the] phrase 'deep time' what timescale pops into your head?" He gathered 23 responses ranging from "more than 10,000 years ago" to "more than 1 billion years ago." That prompted me to ponder this famous term that signifies geologic time. Is it really a number at all, or is it just the vertigo that happens when large numbers come to life? I think John McPhee, who brought "deep time" to our vocabulary in his 1981 book Basin and Range, had it right the very first time he used it: "Numbers do not seem to work well with regard to deep time. Any number above a couple of thousand years--fifty thousand, fifty million--will with nearly equal effect awe the imagination to the point of paralysis."

And yet . . . we seem to do fine discriminating between millionaires, multimillionaires and billionaires. The solar system, explored and sensed by spacecraft for over 50 years, seems like a familiar neighborhood even with its astronomical distances. And while we still recognize the absurdity of a prison sentence of "99 years to life," the legal regulations around nuclear waste have edged into deep time with us barely noticing. Today the law requires the national repository for high-level nuclear waste to be secure for a million years—and we're taking that seriously! Maybe long exposure to geologists really is changing our perspective.

About deep time
An artist's rendition of a million years
How do you teach what a million years is?


August 2, 2013 at 4:02 am
(1) Michael says:

Deep time? Anything that happened before I was born.

August 4, 2013 at 3:42 pm
(2) Michael #2 says:

Deep time? That would be when the deep magic of Narnia was written. In our universe? I’d say a correspondingly ancient time. Or a correspondingly late time. You want to talk about heat death of the universe? If such exists, that’s deep time.

August 4, 2013 at 6:52 pm
(3) Geology Guide says:

I’m officially neutral on where deep time really is, but to me it feels like anything beyond 100,000 years is deep time.

August 4, 2013 at 7:46 pm
(4) gspfo says:

There’s an article in GSA Special Papers 2012, v. 486, p. 19-27, by C. Cervato: “The significance of geologic time: Cultural, educational, and economic frameworks”… might be interesting (google for pdf).

August 8, 2013 at 5:29 pm
(5) Fred says:

Deep Time = Geologic Time for the Great Unwashed.

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