Researchers summarize the likely geological fingerprint of the Anthropocene, and demonstrate that while clear, it will not differ greatly in many respects from other known events in the geological record. They propose tests that could plausibly distinguish an industrial cause from an otherwise naturally occurring climate event.
The researchers define industrial civilizations here as the ability to harness external energy sources at global scales.
One of the key questions in assessing the likelihood of finding such a civilization is an understanding of how often, given that life has arisen and that some species are intelligent, does an industrial civilization develop? Humans are the only example we know of, and our industrial civilization has lasted about 300 years so far. This is a small fraction of the time we have existed as a species, and a tiny fraction of the time that complex life has existed on the Earth's land surface. Complex life has existed for about ∼400 million years ago. This short time period raises the obvious question as to whether this could have happened before. They call this the "Silurian Hypothesis". It is named after a story and species in Dr Who.