ps418

On the evidence for a low oxygen atmosphere prior to about 2.2-2.4bya see New evidence for anoxic Archean atmosphere. For information on the earliest life, particularly microfossil evidence, see this page. A very readable book the subject is William Schopf's book The Cradle of Life.

Patrick

Doubting Didymus

I have to pretty much agree with your assessment of microspheres here. They may play some part in abiogenesis, but I doubt they are themselves the original replicator.

I must admit to not knowing that much about these proteinoids, but exactly how 'protein' like are they? Are they similar enough to normal proteins to be susceptible to prion infection? If so, could that provide a basis for a form of 'inheritance' in microspheres?

Coragyps

SP - The book Cradle of Life by J William Schopf discusses exactly this. He has dug up microfossils from 3.5 Ga and before, with pretty tight constraints on the dating. He also gives the rationale for saying that the atmosphere was almost O2 - free until about 2.2 to 2 Ga - minerals like pyrite and uraninite in the form of "sands" that would have readily dissolved in water in an oxidizing atmosphere, as well as the "banded iron formations" which formed only when the atmosphere was reducing enough to let lots of iron stay in solution in the seas.

Link to book at Amazon.

Dr.GH

There is strong data that the early Earth had a reducing, or minimally, an anoxic atmosphere so that “oxidative degradation” could not occur (Hunten 1993, Kasting 1993, Kump et al 2001 among others, for a contrasting opinion see Ohmoto 1997, and for a direct counter argument to Ohmoto see Holland 1999, for a biochemical study see Des Marais 2000, and for some further theoretical considerations see Dismukes, et 2001, Lasaga, and Ohmoto 2002, ). Further, even had there been a merely anoxic atmosphere, and ocean for that matter, reductive reservoirs would be at least as common as they are today in hydrothermal systems.

Des Marais, David J.
2000 “When Did Photosynthesis Emerge on Earth?” Science 289 (5485): 1703

Dismukes, G. C., V. V. Klimov, S. V. Baranov, Yu. N. Kozlov, J. DasGupta, A.
Tyryshkin.
2001 “The Origin of Atmospheric Oxygen on Earth: The Innovation of Oxygenic Photosynthesis” PNAS-USA vl 98 no. 5: 2170-2175

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

Horita, Juske, Michael E. Berndt
1999 Abiogenic Methane Formation and Isotropic Fractionization Under Hydrothermal Conditions. Science 285 (5430): 1055

Hunten, Donald M.
1993 “Atmospheric Evolution of the Terrestrial Planets” Science 259:915-920

Kasting, J.F.
1993 “Earth's early atmosphere” Science 259: 920-926.

Kump, Lee R., James F. Kasting, Mark E. Barley
2001 “Rise of atmospheric oxygen and the “upside-down” Archean mantle” Geochemistry, Geophysics, Geosystems vol. 2 paper# 2000GC000114

Lasaga, A.C. and Ohmoto, H.
2002 “The oxygen geochemical cycle: dynamics and stability” Geochimica et Cosmochimica Acta vol 66, #3 361-381

Noll KS, Roush TL, Cruikshank DP, Johnson RE, Pendleton YJ.
1997 “Detection of ozone on Saturn's satellites Rhea and Dione. “ Nature, July 3; 388(6637):45-7

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

ps418

To Dr.GH's refs, I'd add these two:

Murakami et al., 2001. Direct evidence of late Archean to early Proterozoic anoxic atmosphere from a product of 2.5 Ga old weathering. Earth and Planetary Science Letters 184(2): 523-528.

Rye, R., and Holland, H. D., 1998. Paleosols and the evolution of atmospheric oxygen: A critical review. American Journal of Science 298(8): 621-672.

Dr.GH

Thanks for the references.

DNAunion

DNAunion: Out of curiosity...

Who accepts and who rejects the statements made about proteinoids and proteinoid microspheres a few posts above, and why?

Doubting Didymus

I'm not sure which ones you mean. You mean your statements, to the effect that proteinoid microspheres are no good as original replicators? I'ts just that there's quite a bit of discussionon microshperes further up.

I'd also like to repeat my question, for anyone who might know:
Is it possible for proteinoid microspheres to be susceptible to prion infection?

DNAunion

DNAunion: I meant "my statements", but I didn't want to actually say "my statements". Why? because I feel many people here would reject them simply because they were mine. I was trying to get people to look at the STATEMENTS, and not at WHO made the statements. I "feared" that if I said, "Who accepts my statements on proteinoid microspheres" the result would have been that no one did.


Who accepts and who rejects my statements on proteinoid microspheres, and why?

Doubting Didymus

Well, I've already given my agreement and I knew full well who you were. Propositions are always to be evaluated on their merits. I will again add the qualifier that prions may provide some semblance of inheritance, but I am not sure microspheres would be susceptible to them.

EDIT: As for 'why' I agree with you, I think that there are some minimum criteria that microshperes do not meet. An evolving population must at LEAST exhibit relatively high fidelity replication, and be mutable at the same time. To be impressive and to produce biodiversity as we know it, the population must also exhibit differential replication efficacy and have a high limit on the possible forms it may take (a replicating clay crystal is all well and good, but if it can never be anything but a clay crystal then evolution is not going to acheive anything interesting).

I think proteinoid microspheres exhibit mutability, obviously, but lack high fidelity replicability. This disqualifys them as evolvable entities.

Now, someone tell me about prions! Am I barking up the wrong tree or what?