Hydrogen Bombshell: Rewriting Life's History

It's a fairly long article so I am only going to post some snippets from it. Really quite interesting!

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Oxygen is supposed to have driven the evolution of complex life – but the discovery of animals that thrive without it tells a different story


These tiny mud-dwellers are far more than a curiosity. They could be the best pointer yet to the origin of complex cells: the basis of most life on Earth, from amoebae to oak trees.



It was not until oxygen levels rose even higher, around half a billion years ago, that the oceans could support large multicellular organisms that got their energy by burning food. That led to the Cambrian explosion, when all kinds of animals appeared. The main point about this story is that it sweeps forward with a magisterial inevitability, waiting only on a rising tide of oxygen.

The broad outlines are true. Oxygen levels did rise in two steps; most eukaryotes do generate energy using oxygen, and are normally tolerant of its toxicity; and the earliest fossil animals did appear soon after a big rise in oxygen levels in the oceans. Yet there are grounds to suspect that oxygen was not the puppet master after all.

One is that the initial rise in oxygen did not cleanse the oceans, but converted them into a stinking mess, full of hydrogen sulphide. Far from having few refuges, anaerobes had whole oceans to themselves. What's more, these conditions lasted for more than a billion years, right through the period when the eukaryotes are thought to have evolved.


Back in the 1970s, Müller discovered that some single-celled organisms have structures that resemble mitochondria but do something quite different; they generate energy without using oxygen, by breaking food down into carbon dioxide and hydrogen - so Müller called them hydrogenosomes.


And now we have found animals that can live without oxygen lurking in brine lakes at the bottom of the Mediterranean. The three yet-to-be-named species were discovered by marine biologist Roberto Danovaro of the Polytechnic University of Marche in Ancona, Italy and his colleagues (BMC Biology, vol 8, p 30). They belong to an obscure group of microscopic animals, the Loricifera, found in ocean sediments around the world.

Indeed, if the hydrogen hypothesis is right, the implications for complex life are striking. The existence of animals that don't need oxygen means that oxygen is not the be-all and end-all of complex life in the universe. The anoxic oceans a billion years ago might have been full of tiny creatures - as indeed many anoxic basins probably are today, if we look properly - and these animals got larger and more active when oxygen levels rose.



New Scientist: [link to www.newscientist.com]