Samples of lava that erupted onto the ocean floor almost 3.5 billion years ago contain microscopic tubes that may have been created by microbes, researchers say. That scenario puts these structures among the oldest known physical remnants of life.
When lava oozes out at midocean ridges where Earth's tectonic plates spread apart, water quickly chills the molten material as it moves across the ocean floor. The pasty rock often solidifies into rounded formations dubbed pillow lava. Marine microorganisms soon colonize the pillow-lava surfaces, where they exploit chemical energy to fuel their metabolism (SN: 11/15/03, p. 315: Attack of the Rock-Eating Microbe