Missing half billion The first evidence of widespread oxygen in the atmosphere occurs in rocks that

Missing half billionThe first evidence of widespread oxygen in the atmosphere occurs in rocks that are about 2.5 billion years old. That time marks one of the major boundaries on the geologic timeline, the boundary between the Achaean and the Proterozoic. However, that time does not match up with the evolution of oxygen producing bacteria. Geologic evidence indicates that organisms producing oxygen as a byproduct existed at least as early as 2.8 billion years ago, a gap of several hundred million years. That difference creates a geologic question; how was life generating oxygen if it didn’t build up in the atmosphere?A team led by Dr. Dawn Sumner from UC Davis investigated a site in Antarctica called Lake Fryxell, in the Dry Valleys of Antarctica. This lake is permanently covered by about 5 meters of ice on average, thin enough for sunlight to get through but thick enough that the waters cannot exchange oxygen with the atmosphere.The team drilled small cores through that layer of ice and widened it using copper heaters to allow divers into the lake. Those divers went deep enough to observe the environment at the bottom, where the environment goes anoxic (no free oxygen in the water).In this environment, the scientists found surprising patches of green; the classic color of photosynthetic organisms. They investigated these patches and found that they were small batches of photosynthetic bacteria. During the long Antarctic summer, a small bit of light gets to these depths and the organisms use that light for energy, giving off oxygen.That tiny bit of oxygen enters the surrounding environment, but it isn’t enough to overwhelm the surrounding anoxic environment. In other words, these pods create a tiny oasis of oxygen around them. A similar environment could explain how oxygen first arrived in the oceans. Tiny bits of oxygen could have formed oases in the ocean over hundreds of millions of years, giving time for other organisms to adapt to the presence of free oxygen in the ocean before the Great Oxygenation Event.-JBBImage credit: Tyler Mackeyhttp://bit.ly/1KuHBAlOriginal paper:http://bit.ly/1ZRUYai -- source link

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