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Questions for Naomi:

I'm having trouble truncating my explanation. In terms of your baseline understanding, are there any deleteable sections which are confusing and/or unnesecary?

Based on the other sections in the 'prebiotic environments' area of History of life, do you think shortening my section is imperative?

I added some small points of knowledge to the other prebiotic environment sections in History of life. Do you think these small points I added aid the information?

I tried my best to hedge my statements with "research shows" instead of "would have"...are there any areas where you still see this needing improvement?

Editorializing was something I tried to cut down on, but are there any areas that still need improvement?


Geothermal Springs

Potential bacterial fossils found on the Allan Hills Meteorite

Geothermal springs can accumulate aqueous phosphate in the form of phopshoric acid. Based on lab-run models, these concentrations of phoshate are insufficient to facilitate biosynthesis[1].


Life Seeded From Elsewhere

Meteorite ALH84001, which was once part of the Martian crust, shows evidence of carbonate-globules with texture and size indicative of terrestrial bacterial activity[2].


Carbonate-rich Lakes

One theory traces the origins of life to the abundant carbonate-rich lakes which would have dotted the early Earth. Phosphate would have been an essential cornerstone to the origin of life since it is a critical component of nucleotides, phospholipids, and Adenosine Triphosphate.[3] Phosphate is often depleted in natural environments due to its uptake by microbes and its affinity for calcium ions. In a process called ‘apatite precipitation’, free phosphate ions react with the calcium ions abundant in water to precipitate out of solution as apatite minerals.[3] When attempting to simulate prebiotic phosphorylation, scientists have only found success when using phosphorus levels far above modern day natural concentrations. [1]

This problem of low phosphate is solved in carbonate-rich environments. When in the presence of carbonate, calcium readily reacts to form calcium carbonate instead of apatite minerals.[4] With the free calcium ions removed from solution, phosphate ions are no longer precipitated from solution.[4]This is specifically seen in lakes with no inflow, since no new calcium is introduced into the water body[1]. After all of the calcium is sequestered into calcium carbonate (calcite), phosphate concentrations are able to increase to levels necessary for facilitating biomolecule creation. [5]

Though carbonate-rich lakes have alkaline chemistry in modern times, models suggest that carbonate lakes had a pH low enough for prebiotic synthesis when placed in the acidifying context of Earth’s early carbon dioxide rich atmosphere.[1] Rainwater rich in carbonic acid weathered the rock on the surface of the Earth at rates far greater than today. [6] With high phosphate influx, no phosphate precipitation, and no microbial usage of phosphate at this time, models show phosphate could have reached concentrations more than 100 times greater than they are today.[1] Modeled pH and phosphate levels of early Earth carbonate-rich lakes nearly match the conditions used in current laboratory experiments on the origin of life. [1]

Similar to the process predicted by geothermal hot spring hypotheses, changing lake levels and wave action deposited phosphorus-rich brine onto dry shore and marginal pools.[7] This drying of the solution promotes polymerization reactions and removes enough water to promote phosphorylation, a process integral to biological energy storage and transfer.[1][7] [8] When washed away by further precipitation and wave action, researchers conclude these newly formed biomolecules may have washed back into the lake - allowing the first prebiotic syntheses on Earth to occur.[1]

  1. ^ a b c d e f g h Toner, Jonathan D.; Catling, David C. (2020-01-14). "A carbonate-rich lake solution to the phosphate problem of the origin of life". Proceedings of the National Academy of Sciences. 117 (2): 883–888. doi:10.1073/pnas.1916109117. ISSN 0027-8424. PMC 6969521. PMID 31888981.{{cite journal}}: CS1 maint: PMC format (link)
  2. ^ McKay, David S.; Gibson, Everett K.; Thomas-Keprta, Kathie L.; Vali, Hojatollah; Romanek, Christopher S.; Clemett, Simon J.; Chillier, Xavier D. F.; Maechling, Claude R.; Zare, Richard N. (1996-08-16). "Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001". Science. 273 (5277): 924–930. doi:10.1126/science.273.5277.924. ISSN 0036-8075.
  3. ^ a b Schwartz, Alan W (2006-09-07). "Phosphorus in prebiotic chemistry". Philosophical Transactions of the Royal Society B: Biological Sciences. 361 (1474): 1743–1749. doi:10.1098/rstb.2006.1901. ISSN 0962-8436.
  4. ^ a b Nathan, Yaacov; Sass, Eytan (1981-11). "Stability relations of apatites and calcium carbonates". Chemical Geology. 34 (1–2): 103–111. doi:10.1016/0009-2541(81)90075-9. ISSN 0009-2541. {{cite journal}}: Check date values in: |date= (help)
  5. ^ Gulbrandsen, R. A. (1969-06-01). "Physical and chemical factors in the formation of marine apatite". Economic Geology. 64 (4): 365–382. doi:10.2113/gsecongeo.64.4.365. ISSN 1554-0774.
  6. ^ Zahnle, K.; Schaefer, L.; Fegley, B. (2010-06-23). "Earth's Earliest Atmospheres". Cold Spring Harbor Perspectives in Biology. 2 (10): a004895–a004895. doi:10.1101/cshperspect.a004895. ISSN 1943-0264.
  7. ^ a b Damer, Bruce; Deamer, David (2020-04-01). "The Hot Spring Hypothesis for an Origin of Life". Astrobiology. 20 (4): 429–452. doi:10.1089/ast.2019.2045. ISSN 1531-1074.
  8. ^ Ross, David; Deamer, David (2016-07-26). "Dry/Wet Cycling and the Thermodynamics and Kinetics of Prebiotic Polymer Synthesis". Life. 6 (3): 28. doi:10.3390/life6030028. ISSN 2075-1729.{{cite journal}}: CS1 maint: unflagged free DOI (link)
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