How deep is deep time? The Silurian Hypothesis explained

The Silurian Hypothesis is a thought experiment which asks whether an ancient industrial civilization have existed (perhaps created, not by humans, but by an entirely different and unknown intelligent species), and whether the remains of such an advanced civilization would be detectable in the geological record. By implication, the Hypothesis also asks if anything will be left of *our* civilization to be discovered by future paleontologists. (The term "Silurian" is not a reference to the geological period, but to a race of hibernating reptoids in the science fiction series "Doctor Who".) 

The answer is rather stunning. When it comes to concrete artefacts or human remains, it's a resounding "no". In a couple of million years, virtually everything human civilization created will be gone with the wind (or rather erosion or decomposition). Since fossilization is very rare, human skeletons might disappear without a trace, too!

However, the chemical signatures of the Anthropocene will remain, for instance mysterious plastic molecules, a curiously high level of the "wrong" carbon atoms, or of  radioactive isotopes. These signatures, signalling the past existence of a polluting industrial civilization, will be found within a sediment layer that's only a few centimeters thick at most!

I admit I had no idea exactly how rare fossils are, or how little of the Earth's surface is *really* old. I did know that our little gadgets are vulnerable to the ravages of time. Still, it's absolutely stunning that an advanced global civilization created by a completely unknown species (reptoids, say) could essentially come and go without us (the all-knowing God species) ever finding out about it. It seems deep time is deeper than I could have imagined!

An ironic fact mentioned by the author is that a more eco-friendly industrial civilization might be forever invisible in the geological record, since only heavy pollution shows up in it. I'm not sure if this is *entirely* correct, though. Maybe inordinately high levels of mined copper and rare earth minerals could give the game away, lol. 

Link follows. 

The Silurian Hypothesis explained