|Biologist Mike Dilger leads a thrilling tour of the subterranean world.|
In the final programme of Wild Underground, our amazing subterranean journey delves even deeper underground; encountering bacteria that survive on a diet of rock and discovering how life survives on the ocean floor in a world totally devoid of light.
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Programme 3. The Rock Eaters
In the final programme of Wild Underground, we travel even deeper underground, well below the earth’s crust, into a world totally devoid of light. Its here, in this seemingly impossibly harsh environment, many kilometers below the surface of the earth that scientists have recently discovered unusual microbes that thrive at such depths. These findings have forced us to re-draw the evolutionary tree of life and question where life itself really began. Its time to meet the rock eaters, extremophiles and the world of SLiMES!
The programme opens to the sounds of a Volcanic explosion. Lava is spewed out and flows across the horizon, cutting deep channels into the landscape. As the lava flows, the outer layers cool and harden, whilst the hot molten lava flows on. After several months, the result is a giant, hollow tube in some places the size of a train tunnel. These giant lava tubes, which are largely underground, are found associated with volcanic islands like Hawaii. Plants colonise the outside of these tubes and their long roots penetrate the walls of the tube and hang down into the cavities. Insects then colonise these tubes: including crickets and plant hoppers. In the complete darkness of the lava tube, animals have adapted to thrive in these alien underground conditions. Blind spiders move slowly amongst the roots, feeling for the vibration of the prey, whilst plant hoppers use a type of morse code, causing vibrations across the network of roots, to find and recognize each other in the darkness.
Life at the bottom of the ocean floor also has to survive extreme conditions. As in the lava tubes, sunlight does not penetrate to the ocean floor, but there’s another challenge. The pressure from the weight of all the water is hundreds of times greater than we experience at sea level. Until recently, scientists thought that little life could exist under such conditions now we know otherwise, when scientists discovered scalding water billowing from hydrothermal vents on the seafloor. Surrounding these underwater geysers were clusters of bizarre animals completely new to science including tubeworms and giant clams.
Hydrothermal vents form in places where there is volcanic activity. Paul Tyler, Professor of Deep Sea Biology, Southampton Oceanography Centre at the University of Southampton, recalls a journey down to these vents and describes how organisms survive here. The answer lies with the hydrothermal fluids. Bacteria extract chemicals from the fluid such as hydrogen sulphide, and use this chemical energy to manufacture sugars in a process called chemosynthesis. These bacteria form the base of the food chain. Some animals, like the tubeworms and clams have formed a symbiotic relationship with these bacteria ie the bacteria live in the “guts” of the animals. The tubeworms provide the bacteria with hydrogen suphide and oxygen and then use some of the sugars the bacteria produce as food.
Also deep down in the sediments of the marine environment are other organisms which eek out a living in the absence of light, and produce methane gas as a by-product of their metabolism. These menthanogens as they are called, are similar to those found in cows to aid their digestion!
Scientists have also discovered that organisms can survive deep down in the rocks of mines in South Africa, the basalt rocks of the Columbia basin, and deep under the sea. The common feature of these organisms is that their metabolism is quite unlike anything found above ground: because they do not have light as source of energy for their metabolism, and they are deprived of oxygen.
These bacteria which have been identified, can in essence, feed off rock. These subsurface lithographic microbial ecosystems (SLiMES, for short), are proving to be of enormous interest to science as they provide a model for the existence of contemporary life on Mars, because basalt rock, liquid water and bicarbonate (the essential ingredients for these microbes to function) are believed to be present within the Martian subsurface …. So rather then life beginning above ground, could it have started below ground … and if there is life below ground on THIS planet is it not possible that life may exist on other planets …what’s below our feet is proving even more fascinating than what is above ground, and even revolutionizing our ideas about the origin and evolution of life itself.
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Microbes deep inside the Earth, Scientific American, Oct 1996, p42-47
Natural History Museum of Berlin
Southampton Oceanography Centre
Woods Hole Oceanographic Institution
Idaho National Engineering and Environmental Laboratory
U.S. Department of Energy
Portland State University
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