The Earth after us – man’s legacy in the rocks

Author: Jan Zalasiewicz.

Editor: Derek Gobbett.

Jan considered the possibility of aliens visiting the earth in 100 million years time and posed the question “What would they discover about the long extinct humans?” Nothing would be preserved on the eroded surface of the continents, but in the strata laid down in the seas and subsiding continental basins, traces and even body fossils recording man’s brief existence would be preserved.

The exponential curve of increasing CO2 emissions would have affected the chemistry of the rocks. Shelly fauna would have been affected by the acidification of the oceans. The loss of biodiversity probably leading to a major extinction event might be as evidently catastrophic as the late Permian extinction.

Trace fossils in the sediments could include boot prints, buildings and even whole cities submerged beneath rising sea levels. Body fossils of bones and artefacts of wood, stone and even imprints of delicate materials such as woven fabric would be preserved in fine sediments as carbon films and imprints. The evidence to support these ideas was in the past. We know that very fragile remains of organisms, for example graptolites, dragonfly wings and worms have been preserved for hundreds of millions of years.

An unusual perspective for geologists, using the past as the key to the future, this talk was very thought provoking and it generated numerous questions from the floor.