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Imagine Earth without people

Humans are undoubtedly the most dominant species the Earth has ever known. [...] And we're leaving quite a mess behind: ploughed-up prairies, razed forests, drained aquifers, nuclear waste, chemical pollution, invasive species, mass extinctions and now the looming spectre of climate change. If they could, the other species we share Earth with would surely vote us off the planet.

Now just suppose they got their wish. [...] Left once more to its own devices, Nature would begin to reclaim the planet, as fields and pastures reverted to prairies and forest, the air and water cleansed themselves of pollutants, and roads and cities crumbled back to dust.

"The sad truth is, once the humans get out of the picture, the outlook starts to get a lot better," says John Orrock, a conservation biologist at the National Center for Ecological Analysis and Synthesis in Santa Barbara, California. But would the footprint of humanity ever fade away completely, or have we so altered the Earth that even a million years from now a visitor would know that an industrial society once ruled the planet?

In other words, if an alien ship would find the Earth a millions years after our extintion, what traces would they find of our existence? What they would conclude about our civilization or intelligence?

by das monde on Fri Oct 13th, 2006 at 06:55:51 AM EST
They would find concrete structures (cities, roads) buried under a million years of sediment, and steel fossils. And the footprint of mining operations.

It would be quite obvious, I think. A million years is nothing in geological time, and our geological foorprint is quite extensive.

Those whom the Gods wish to destroy They first make mad. -- Euripides

by Migeru (migeru at eurotrib dot com) on Fri Oct 13th, 2006 at 07:00:21 AM EST
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What Migeru said. I'd add that any core sample through the right layers in seabed sediments or (much later) rock would show clear markers of chemicals, soot, and strange particles of various sorts.

"The sad truth is, once the humans get out of the picture, the outlook starts to get a lot better..."

The collision of human beings with the natural biosphere is ugly, getting worse, and has enormous momentum. Looking at what's already happened, consider that agriculture has consumed enormous areas, and that it has (of course) selectively destroyed regions of high biological productivity. For similar reasons, we tend to think of "primitive" people as living in hostile environments -- the arctic, deserts, mountains, hell-holes of tropical disease -- but this is because the nicer places were quickly grabbed by more powerful cultures, and largely for agriculture.

Words and ideas I offer here may be used freely and without attribution.

by technopolitical on Fri Oct 13th, 2006 at 04:24:06 PM EST
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An alien species, capable of interstellar travel, would probably have sensors good enough to locate a number of artifacts in space in and around the solar system (remember Voyager 1 and Voyager 2, at least, are in the process of leaving the solar system), as well as some on the Moon. In vacuum conditions these should be identifiable for millions of years.

A careful examination of the fossil record and the distribution of species around the planet, would also reveal an era (in geological terms extremely brief) of unusually rapid long distance migrations of plants and animals; as well as the mass extinction). This is evidence independent of the direct discovery of fossil humans and human artifacts.

I suspect all these strands of evidence would be diagnostic of an intelligent species which was not wise enough to avoid global catastrophe.

Of course, as the ultimate technological fix, we might have downloaded our minds to machines or created artificial intelligences as our successors; so the aliens could get a first hand account of what happened.

by Gary J on Sat Oct 14th, 2006 at 02:26:42 PM EST
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If the extintion thing will happen fast, there will be just a few artificial objects outside Earth's gravity. Vast majority of satelites will be burned in the atmosphere by then. But we may indeed have left enough objects near geostationary orbits - and that would be a convincing indication of intelligence.

One funny possibility is that we would leave enough evidence to suspect existence of our civilisation of this level, but not enough to establish it up to scientific certainty. We can imagine a bunch of rather gifted allien enthusiasts of Terrestial civilisation being derided by their scientific "establishment" :-)))

Intelligence detection is an interesting problem for science. Positive confirmation by single artifacts looks more feasible than falsification of the hypothesis by single observations. What would Popper say?

by das monde on Mon Oct 16th, 2006 at 10:35:39 PM EST
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