Was There a Civilization On Earth Before Humans? (theatlantic.com)

Adam Frank, writing for The Atlantic: We're used to imagining extinct civilizations in terms of the sunken statues and subterranean ruins. These kinds of artifacts of previous societies are fine if you're only interested in timescales of a few thousands of years. But once you roll the clock back to tens of millions or hundreds of millions of years, things get more complicated.

When it comes to direct evidence of an industrial civilization -- things like cities, factories, and roads -- the geologic record doesn't go back past what's called the Quaternary period 2.6 million years ago. For example, the oldest large-scale stretch of ancient surface lies in the Negev Desert. It's "just" 1.8 million years old -- older surfaces are mostly visible in cross section via something like a cliff face or rock cuts. Go back much farther than the Quaternary and everything has been turned over and crushed to dust.

And, if we're going back this far, we're not talking about human civilizations anymore. Homo sapiens didn't make their appearance on the planet until just 300,000 years or so ago. [...] Given that all direct evidence would be long gone after many millions of years, what kinds of evidence might then still exist? The best way to answer this question is to figure out what evidence we'd leave behind if human civilization collapsed at its current stage of development. Mr. Frank, along with Gavin Schmidt, Director of the NASA Goddard Institute for Space Studies, have published their research on the subject [PDF].

Comments

No (evidence: coal is still there)

[Anonymous Coward]

Short answer? No. Not on any scale like our current civilization.

Evidence: the coal is still here for us to burn. :P And there's no plastic in lake and sea sediments. :P

Re:No (evidence: coal is still there)

[jwhyche]

But where is the space-junk?

You are assuming they existed long enough to reach a space age. They may have just reached the age of steam then collapsed. The fact they they failed to do something about the incoming asteroid would support this clam.

There is another answer too. If they did reach the space age they might have simply been more tidy about space than we are. Plus a 70+ million years is plenty of time for all orbital space junk to fall back to earth.

Re:No (evidence: coal is still there)

[sdinfoserv]

No, but simple things like glass from a leaded glass window would survive. As a matter of fact ALL our resources that we extract from the ground were intact when we started mining them. So unless all they used was trees and grass, we are the only advanced society.

Re:No (evidence: coal is still there)

[Immerman]

Why would you assume space junk would stay up for many millions of years? Anything remotely close to Earth would have long since deorbitted due to atmospheric and/or magnetic drag. Even out near geostationary, millions of years of perturbations by the moon's gravity and solar wind could easily have destabilized the orbits.

Re:No (evidence: coal is still there)

[jwhyche]

There would be no secrecy. You maybe able to keep government source like NASA silent. You would still have to deal with all the university astronomy projects. But lets say you managed to keep the university programs secret, then you need to deal with the hundreds of thousands of amateur astronomers.

An these are only U.S. based projects. There are still 200 countries in the world, most with their own astronomy programs. You are not going to keep a extinction level asteroid secret for long.

Re:We would know it.

[DavenH]

The paper addresses this geological impact paradox. For the signal to be obvious in the geological record, it has to be sustained, but for a civilization to persist long enough to be obvious in geological time scales, they have to be in equilibrium with the environment.

Re: Yeah, dinasaurs

[amicusNYCL]

We were the first to mine coal, drill for oil, extract deposits of rare earths, and precious metals.

Citation needed.

Also, some things shouldn't go missing. Tracks on the moon

Why would they have necessarily gone to the moon, and even more importantly, why would one of our very few manned missions, or other landing craft, have landed in the right place to have seen those tracks? If we're talking about the scale of millions of years, wouldn't an impact on the moon be an obvious candidate for removing evidence?

orbital satellites

Satellites in a stable orbit for millions of years? The moon is not in a stable orbit when you're talking about geologic time.

undecomposable manmade polymers and alloys

I don't think we've made anything that would be considered "undecomposable" after millions of years. Moreover, even if we could, wouldn't they be buried after millions of years instead of sitting on the surface?