[MunichEast]

The first footprints of Homo sapiens are still fresh in the dirt. Our species dates back around 300,000 years and our industrial capabilities less than 300. We are latecomers to a planet that has circled the Sun for 4.5bn years. Time enough, some speculate, for previous civilisations to have developed — and then vanished without a trace.

This is the provocative starting point adopted by Gavin Schmidt, from the Nasa Goddard Institute of Space Studies, and Adam Frank, an astrophysicist at the University of Rochester. How, they ask, could we tell whether civilisations have risen and fallen on earth millions of years before us? And what permanent geological legacy might we humans one day leave behind?

Their thought experiment is published in the International Journal of Astrobiology. The researchers discuss various tests for the Silurian hypothesis, the name they give to the idea that humans were preceded by other advanced cultures (inspired by a Dr Who episode featuring a buried race of intelligent reptiles, awakened by a nuclear reactor).

The starting point is this: the rocks beneath our feet probably constitute an incomplete encyclopedia of terrestrial history. Over the past 2.5m years, the geological record shows evidence of climate change, different soils, and fragments of older hominid cultures, such as Neanderthals and Denisovans. But, the further we turn back the clock, the sparser the physical remnants become. Any objects belonging to civilisations dating back more than 4m years, they suggest, are probably lost to the land and the elements. The constant churning of the ocean crust also makes underwater sediments unreliable repositories of prehistoric secrets.

We know of the existence of dinosaurs through fossils — but only a tiny fraction of life was thus preserved. Steamy climates and soft tissue lessened the likelihood of entombment — and only a few thousand near-complete dinosaur specimens exist to represent creatures that first evolved around 250m years ago and became extinct around 65m years ago. Were sapiens to suddenly disappear, it is uncertain whether our shortlived species would surface in the fossil record even a million years from now.

The existence of past terrestrial inhabitants might, though, be given away by distinctive chemical traces. Humans are changing the environment thanks to man-made substances, such as plastics. Atomic bombs leave radioactive fingerprints. The burning of fossil fuels also constitutes an obvious chemical sign of industrial activity: it alters the ratio of carbon-13 to carbon-12 in the atmosphere. These lingering hallmarks have led to the idea, not yet formally ratified, that we have exited the Holocene and entered a new geological era called the Anthropocene.

Mr Schmidt and Mr Frank suggest that any industrial civilisation would, by definition, need to harness energy on a large scale. There was a massive release of carbon into the atmosphere around 56m years ago, which coincided with a dramatic rise in global temperature and mass extinction of marine life.

A carbon spike is not a sufficient pointer to past civilisations, however — volcanic activity can produce a similar signature by heating and unlocking carbon-rich ocean sediments. Besides, any culture sophisticated enough to become industrialised might have tapped the near-infinite power of the wind, the waves or the sun.

Herein lies a paradox: now that we know we are altering the environment, we are taking steps to eradicate and mitigate these changes. As we develop the idea of sustainability, our environmental footprint might diminish. It could be that the longer sapiens survive, the less visible the mark we leave in the geological record. That’s a provocative thought: the ultimate legacy of a truly advanced civilisation might be no legacy at all.

The writer is a science commentator
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Durch Zufall bin ich über diesen Artikel gestolpert, der 2018 in der Financial Times erschienen war und möchte ihn mit euch teilen.

Wir alle wissen das es vor der Zeit der Säugetiere eine andere dominierende Spezies gab, die fast vollständig ausgelöscht wurde. Nun ist es eine interessante Frage, wieso wir uns so sicher sind das Menschen die erste intelligente Lebensform mit Zivilisation auf diesem Planeten war ? Die Menschheit ist blutjung auf diesem Planeten und gab es vielleicht doch andere vor uns ?

[elise]

naja... meinen schülern sage ich ja immer, dass der mensch eines der dümmsten lebewesen auf dem planeten ist - alle anderen erhalten ihren lebensraum...

sollte es andere vor uns gegeben haben, haben sie zumindest keine so deutlichen spuren hinterlassen wie wir... oder sie waren lange, lange vor uns da.... ich fände es gut, anzunehmen, dass noch andere vor uns da waren (über die intelligenz möchte ich jetzt nix sagen) das würde uns die einzigartigkeit nehmen... täte uns gut!