The earliest seafloor hydrothermal vents - supposedly more than three billion years old - may be nothing more than deposits from underground springs active in the last few thousand years. That is the claim of two US geologists who carried out a new analysis of rocks from South Africa which were previously dated to the Archaean period - when life first began to diversify. The findings could have important implications for our understanding of the early Earth and the microbial life forms that lived there. But one authority on the geology of the Barberton greenstone belt - where the rocks are found - launched a vigorous defence of evidence that they contain ancient hydrothermal vents. Seafloor hydrothermal vents emit jets of mineral-rich water that has been superheated to up to 400 Celsius by submarine volcanoes.

They drive an extraordinary ecosystem in which bacteria process the water to support a range of deep-water creatures that live in total darkness. Many scientists believe the vents could explain how life first got a foothold on Earth and may even provide an opening for life on other planets which appear on the surface to be uninhabitable.

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