Recently discovered fossil worm burrows reveal that, in the right sediment, life can survive far deeper than imagined

Sandstone outcrops in the Karoo Basin, in southern South Africa. Photograph: David Hodgson/University of Leeds

Blue Planet II gave us a glimpse of the weird and wonderful life that swims and floats in the deep ocean, but what about the creatures that live beneath the ocean floor? Present day surveys suggest that shrimps and worms inhabit the top tens of centimeters of seabed, but it was assumed that life couldn’t survive much beyond 2m of sediment. However, recently discovered fossilised burrows show that, given the right kind of sediment, life can survive far deeper. Have we been looking in the wrong places for seabed critters?

Sarah Cobain from the University of Leeds and colleagues analysed ancient burrow systems, found in South African rocks that were part of the ocean floor around 250m years ago. Writing in Scientific Reports they reveal that worm-like creatures lived up to 8m below the seabed, and must have burrowed for hours or even days. The burrows were in sand sheets, which are widespread on modern ocean floors. “There is every reason to think life could exist at similar depths in modern sand deposits, but we don’t know, as marine biology investigations tend to focus on muddy substrates,” says co-author David Hodgson.