Freethought & Rationalism Archive

ps418 · 12-28-2002, 09:53 AM

New sulpher isotopic evidence for very low oxygen Archean atmosphere. The new evidence is in the form of sulpher isotopic ratios preserved in sulphide inclusions in diamonds from the Orapa kimberlite mine.

Earth's early atmosphere

Quote:

There is considerable evidence that before 2400 million years ago, oxygen was at best a minor component (less than 1%) of Earth's atmosphere. The subsequent onset of "red beds" (sediments with a red color from iron oxidation) and oxidized "paleosols" (soil horizons) and the disappearance of detrital pyrite, uraninite, and siderite have been attributed to the rise of oxygen (1, 2). But not all geologists accept this evidence. It has, for example, been argued that the oxygen content was at least 50% of the present atmospheric concentration throughout the last 4000 million years (3).

The recent discovery of mass-independent fractionation in the isotopic composition of sulfur in sedimentary iron sulfides (pyrite) and sulfates makes a change in the oxygen content of the atmosphere between 2400 to 2100 million years ago almost inevitable (4-7). The rate of chemical reactions usually depends on the mass of the atoms or molecules involved, and thus changes slightly for isotopically substituted but otherwise identical molecules. Only one natural process is known to produce mass-independent sulfur isotope effects: atmospheric photochemical reactions in the absence of ozone or oxygen, which shield the atmosphere from the ultraviolet (UV) radiation required for the reactions.

Also:

Calibration of Sulfate Levels in the Archean Ocean

Mass-Independent Sulfur of Inclusions in Diamond and Sulfur Recycling on Early Earth

Jobar · 12-28-2002, 02:12 PM

I thought it was long established that high O2 / low CO2 is a result of photosynthesis. Who argues for a pre-biotic oxygen atmosphere, and how do they explain the maintenance of oxygen levels without photosynthesis?

lpetrich · 12-28-2002, 03:12 PM

They're claiming that this is evidence for low concentration (<1%), not oxygen concentration comparable to the present day's.

A mechanism that can create free oxygen is photodissociation of water; the hydrogen may evaporate into outer space, leaving the oxygen behind.

Dr.GH · 12-28-2002, 04:55 PM

Thanks for the links. I was going to spend the day drinking beer and playing games. Instead, I spent the day drinking beer and downloading articles.

Oh Boy!

jobar, Let me try to get to you in the AM. It involves J. Wells and the Icons of Evolution, Chp. 2 crap as well as the abiogensis as opposed to evolution, the Baumgardener flood/continental subduction model, the only living early high O2 advocate (Hiroshi Omotto), and a bunch of other stuff. OR, somebody else could do it (please???).

GH

Bubba · 12-28-2002, 06:26 PM

Thanks for excellent links again, Patrick.

Chris

Dr.GH · 12-29-2002, 02:17 PM

Quote:

I thought it was long established that high O2 / low CO2 is a result of photosynthesis. Who argues for a pre-biotic oxygen atmosphere, and how do they explain the maintenance of oxygen levels without photosynthesis?

Jobar, Jon Wells in his book [i]The Icons of Evolution� echos the argument of his master, Phillip Johnson, in Darwin on Trial that the Miller/Urey experiment is the only line of inquirey on the origin of life, that the Miller/Urey experiment �failed� because it did not creat life, and that without the strongly reduced gas mixture used by Miller and Urey there could be no organic moleculles produced. Wells extends his argument to the point of absurdity by claiming that any elemental oxygen in the early atmosphere would preclude the abiotic formation of complex hydrocarbons.

The only living scientist to argue for an early oxic atmosphere is Hiroshi Ohmoto and some of his students ( sample papers cited below). He has been countered by Holland 1997 among others.

What is interesting about the Farquhar et al paper that Patrick brought to our attention is that it supports the heterogeneity of the mantle, and extends the data reported by Canil. This is particularly relevent to the results reported by Delano, who argues that the volcanic outgasing in the Hadean and Archean could not have provided a strongly reduced atmosphere. Wiechert�s commnetary also points out additional interests, including the observation that the results of Farquhar et al , and Habicht et al taken together seem to rule out significant ammonia concentrations in the lower Archaen atmosphere and that there could be significant uV radiation even at the Earth�s surface. These last two points raise issues for the original Miller/Urey experiment's significance to the OOL. But Miller, as well as others, have repeatedly shown that complex molecules can form under less reduced conditions, and even the original apparatus produes interesting molecules with different gas mixtures.

Canil, Dante
2002 �Vanadium in peridotites, mantle redox and tectonic environmnets: Archean to
present� Earth and Planetary Science Letters 195 (2002) 75-90.

Delano, John W.
2001 �Redox History of the Earth�s Interior since ~3900 Ma:Implications for Prebiotic
Molecules� Origins of Life and the Evolution of the Biosphere v.31(4-5):311-341

J. Farquhar, B. A. Wing, K. D. McKeegan, J. W. Harris, P. Cartigny, and M. H. Thiemens
2002 Mass-independent Sulfur of Inclusions in Diamond and Sulfur Recycling on Early
Earth Science 2002 298: 2369-2372

Holland, Heinrich D.
1999 �When did the Earth�s atmosphere become oxic? A Reply.� The Geochemical
News #100: 20-22

Kirsten S. Habicht, Michael Gade, Bo Thamdrup, Peter Berg, and Donald E. Canfield
2002 Calibration of Sulfate Levels in the Archean Ocean Science 298: 2372-2374

Ohmoto, H.
1996 Evidence in pre-2.2 Ga paleosols for the early evolution of atmospheric oxygen and
terrestrial biota. Geology, 24:1135-1138

Ohmoto, H.
1997 �When Did the Earth�s Atmosphere Become Oxic?� The Geochemical News, 93:
12-13, 26-27.

Uwe H. Wiechert
2002 Earth's Early Atmosphere Science 298: 2341-2342

Coragyps · 12-29-2002, 02:38 PM

While we're on early, early life, the newest Nature (vol 420, pp 841-844, 19/26 Dec 2002) has an article by J S Reader and G F Joyce titled "A ribozyme composed of only two different nucleotides."
Abstract:

Quote:

RNA molecules are thought to have been prominent in the early history of life on Earth because of their ability both to encode genetic information and to exhibit catalytic function. The modern genetic alphabet relies on two sets of complementary base pairs to store genetic information. However, owing to the chemical instability of cytosine, which readily deaminates to uracil, a primitive genetic system composed of the bases A, U, G and C may have been difficult to establish. It has been suggested that the first genetic material instead contained only a single base-pairing unit. Here we show that binary informational macromolecules, containing only two different nucleotide subunits, can act as catalysts. In vitro evolution was used to obtain ligase ribozymes composed of only 2,6-diaminopurine and uracil nucleotides, which catalyse the template-directed joining of two RNA molecules, one bearing a 5'-triphosphate and the other a 3'-hydroxyl. The active conformation of the fastest isolated ribozyme had a catalytic rate that was about 36,000-fold faster than the uncatalysed rate of reaction. This ribozyme is specific for the formation of biologically relevant 3',5'-phosphodiester linkages.

Dr.GH · 12-29-2002, 09:08 PM

A good article. I was interested that there were only 3 guanine locations in the original ribozyme that could not be substituted without loss of catalytic function

Dr.GH · 12-29-2002, 09:08 PM

opps

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12-28-2002, 02:12 PM	#2
Jobar Veteran Member Join Date: Jun 2001 Location: secularcafe.org Posts: 9,525	I thought it was long established that high O2 / low CO2 is a result of photosynthesis. Who argues for a pre-biotic oxygen atmosphere, and how do they explain the maintenance of oxygen levels without photosynthesis?

12-28-2002, 03:12 PM	#3
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	They're claiming that this is evidence for low concentration (<1%), not oxygen concentration comparable to the present day's. A mechanism that can create free oxygen is photodissociation of water; the hydrogen may evaporate into outer space, leaving the oxygen behind.

12-28-2002, 04:55 PM	#4
Dr.GH Veteran Member Join Date: Jul 2001 Location: Dana Point, Ca, USA Posts: 2,115	Thanks for the links. I was going to spend the day drinking beer and playing games. Instead, I spent the day drinking beer and downloading articles. Oh Boy! jobar, Let me try to get to you in the AM. It involves J. Wells and the Icons of Evolution, Chp. 2 crap as well as the abiogensis as opposed to evolution, the Baumgardener flood/continental subduction model, the only living early high O2 advocate (Hiroshi Omotto), and a bunch of other stuff. OR, somebody else could do it (please???). GH

12-28-2002, 06:26 PM	#5
Bubba Veteran Member Join Date: Mar 2001 Location: Orient, OH USA Posts: 1,501	Thanks for excellent links again, Patrick. Chris

12-29-2002, 09:08 PM	#8
Dr.GH Veteran Member Join Date: Jul 2001 Location: Dana Point, Ca, USA Posts: 2,115	A good article. I was interested that there were only 3 guanine locations in the original ribozyme that could not be substituted without loss of catalytic function

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