Plant-like bacteria existed in the oceans for hundreds of millions of years while the Earth’s air was not fit to breathe, research suggested today. Life evolved at least 200 million years before oxygen began to build up in the atmosphere, a study has shown.
During this period in its history, known as the Archaean, the Earth was covered by a poisonous smog of methane, ammonia and other toxic gases.
Similar conditions exist today on Saturn’s moon Titan. Life as we know it today could not have survived on the early Earth.
The new study involved an analysis of ancient preserved seabed rocks from South Africa dating back two to three billion years.
US scientists at Rutgers University in New Brunswick, New Jersey, found chemical evidence of nitrogen cycles that could not have taken place without the presence of free oxygen.
Nitrogen cycles relate to the way living things obtain and use nitrogen to produce complex organic molecules. Evidence of nitrogen cycles provides a ”fingerprint” of life.
The researchers, Dr Linda Godfrey and Dr Paul Falkowski, concluded that organisms which produced oxygen as a by-product of photosynthesis must have evolved by around 2.5 billion years ago.
Oxygen did not begin to enrich the atmosphere until at least 200 million years later.
The scientists wrote in the journal Nature Geoscience: ”Nitrogen is a relatively inert molecule and has an atmospheric lifetime of the order of around one billion years. In contrast, oxygen.. is highly reactive and must be produced continuously by oxygenic photosynthesis.
”It is unlikely that the gas was present above trace levels in the atmosphere of the Earth during the first two billion years of the planet’s history, but when oxygenic photosynthesis first arose on the Earth is not known with certainty.”
If we are looking to re-create the way life appeared on earth, it seems we need to look for life forms that can exist in a smog of methane, ammonia and other toxic gasses for 200 million years. This makes Titan very interesting. Is there some bizarre form of life on Titan similar to the earliest life on our planet?
In 1954, J. B. S. Haldane, speaking at the Symposium on the Origin of Life, suggested that an alternative biochemistry could be conceived in which water was replaced as a solvent by liquid ammonia. Part of his reasoning was based on the observation that water has a number of ammonia analogues. For example, the ammonia analogue of methanol, CH3OH, is methylamine, CH3NH2. Haldane theorized that it might be possible to build up the ammonia-based counterparts of complex substances, such as proteins and nucleic acids, and then make use of the fact that an entire class of organic compounds, the peptides, could exist without change in the ammonia system. The amide molecules, which substitute for the normal amino acids, could then undergo condensation to form polypeptides which would be almost identical in form to those found in terrestrial life-forms. This hypothesis, which was developed further by the British astronomer V. Axel Firsoff, is of particular interest when considering the possibility of biological evolution on ammonia-rich worlds such as gas giants and their moons (see Jupiter, life on).
On the plus side, liquid ammonia does have some striking chemical similarities with water. There is a whole system of organic and inorganic chemistry that takes place in ammono, instead of aqueous, solution. Ammonia has the further advantage of dissolving most organics as well as or better than water, and it has the unprecedented ability to dissolve many elemental metals, including sodium, magnesium, and aluminum, directly into solution; moreover, several other elements, such as iodine, sulfur, selenium, and phosphorus are also somewhat soluble in ammonia with minimal reaction. Each of these elements is important to life chemistry and the pathways of prebiotic synthesis. The objection is often raised that the liquidity range of liquid ammonia – 44°C at 1 atm pressure – is rather low for biology. But, as with water, raising the planetary surface pressure broadens the liquidity range. At 60 atm, for example, which is below the pressures available on Jupiter or Venus, ammonia boils at 98°C instead of -33°C, giving a liquidity range of 175°C. Ammonia-based life need not necessarily be low-temperature life! …
– via daviddarling