Rocks show life could have flourished on Earth 3.2 billion years ago

[gary]

A University of Washington press release by Hannah Hickey dated Feb 16 2015
discusses a paper published in Nature that raises the possibility that
life on Earth may have appeared much earlier than generally thought.

Originally Posted by Hannah Hickey, University of Washington

The authors analyzed 52 samples ranging in age from 2.75 to 3.2 billion years old, collected in South Africa and northwestern Australia. These are some of the oldest and best-preserved rocks on the planet. The rocks were formed from sediment deposited on continental margins, so are free of chemical irregularities that would occur near a subsea volcano. They also formed before the atmosphere gained oxygen, roughly 2.3 to 2.4 billion years ago, and so preserve chemical clues that have disappeared in modern rocks.

Even the oldest samples, 3.2 billion years old – three-quarters of the way back to the birth of the planet – showed chemical evidence that life was pulling nitrogen out of the air. The ratio of heavier to lighter nitrogen atoms fits the pattern of nitrogen-fixing enzymes contained in single-celled organisms, and does not match any chemical reactions that occur in the absence of life.

Press release here -
http://www.washington.edu/news/2015/...ion-years-ago/


Paper here in Nature provided under their recent "content sharing initiative"
entitled "Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr" -
http://www.nature.com/articles/natur...O4KeZUw8TprrnH

[madbadgalaxyman (Robert)]

Thanks for the interesting post, Gary. It does seem that the estimated time of various critical waypoints during the evolution of life has a tendency to be pushed back, with further research.
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In this post, I provide some non-technical explanatory notes suitable for people without a substantial background in chemistry and biology. (here I cast aside my madbadgalaxyman persona and put on my "madbioman" outfit ! )

So....what is Nitrogen Fixation that I should be mindful of it?

Nitrogen is critically important for the survival of all living things, with nitrogen atoms being an essential component of amino acids, proteins, DNA, etc.

Oddly, Nitrogen makes up the majority of the Earth's atmosphere, but it is rare in the rocks of the Earth.

The diatomic nitrogen molecule which makes up the majority of the air we breath (about 3/4 of the air is nitrogen gas, by volume) has a strong triple bond between its two atoms which makes it very hard for its two linked nitrogen atoms to be separated. Thus, nitrogen molecules tend to be chemically inert.
Therefore, atmospheric nitrogen must be processed or "fixed", in order that the nitrogen atoms can be used by plants.

Some species of bacteria that live symbiotically in the roots of plants , and also certain types of bacteria found in the soil, contain biochemical machinery which breaks down the molecular nitrogen gas of the atmosphere into that specific form of nitrogen which is necessary and essential for plant life to survive and metabolize. In other words, it is absolutely necessary for plants to obtain nitrogen in the appropriate form in order that they should live, and the nitrogen has to be "fixed"; that is, the nitrogen has to be converted into a form where it can be utilized by plants. (Indeed, nitrogen availability is one of the critical limiting factors in nearly all ecosystems, and the amount of nitrogen (in available form) is a very major control on plant growth.)
This conversion of nitrogen into a form that is useful to plants is done using an enzyme called nitrogenase, which uses atmospheric nitrogen molecules to make that specific form of nitrogen which can be utilized by plants; ammonia. (note: this statement is rather oversimplified)
In chemistry jargon, this process is known as the "enzymatic reduction of dinitrogen to ammonia", and the nitrogenase enzyme ultimately acts to bond each atom of nitrogen to three atoms of hydrogen, thus forming molecules of ammonia ( hopefully we learned at school that the ammonia molecule is composed of one nitrogen atom plus three hydrogen atoms. ).

Therefore , nitrogenase is an absolutely essential molecule for the sustenance of all living things. So those bacteria that contain nitrogenase (e.g. various cyanobacteria, green sulfur bacteria, rhizobia, Frankia) accomplish an important chemical reaction, without which much of the life on our planet would not exist.

Bacteria which can convert nitrogen into the useable form that is necessary for plant growth & metabolism can be either free-living, or symbiotic with plant roots. The best known example of symbiotic nitrogen-processing bacteria is Rhizobium, which live symbiotically in the root nodules of legumes, and these Very Very Clever root bacteria can increase the fertility of poor soils by increasing their nitrogen content. (the genus of these bacteria is Rhizobium, and there are various species of Rhizobium bacteria)

Remarkably, there is only one known family of enzymes that accomplishes this vital process. Furthermore, the activity of the nitrogenase enzyme is very strongly diminished in the presence of oxygen, so some root nodules actually contain a form of haemoglobin to absorb the oxygen, which allows the bacteria to get on with their nitrogen conversion trick !!
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OK folks, how did I do with my non-technical explaining of nitrogen fixation.?
Have any of you "biochemistry" specialists got any criticisms or further comments?)

Sincerely yours,
madbadgalaxyman
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[ZeroID (Brent)]

Wow ! I actually understood all that. Well done madbioman..!

And yes, interesting as well.

Cheers

[madbadgalaxyman (Robert)]

Thanks, Brent,
glad you found my science writing to be illuminating.

The essence of good science writing is to make the concepts very clear in the mind of the reader; oddly, there are few people who have this type of writing talent. Unfortunately, the most typical sort of science writing makes the relatively straightforward concepts of science sound much much harder than they really are.

- Robert

[mental4astro (Alexander)]

WOW! I'm with Brent here!

Amazing article noted by Gary, and outstanding explanation by Maddie,

Very enlightening stuff. Thanks gentlemen

Mental.