Ideas and perspectives: Development of nascent autotrophic carbon fixation systems in various redox conditions of the fluid degassing on early Earth
<p>The origin and development of the primary autotrophic metabolism on early Earth were influenced by the two main regimes of degassing of the Earth – reducing (predominance <span class="inline-formula">CH<sub>4</sub></span>) and oxidative (<span class=&quo...
| Main Authors: | , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-04-01
|
| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/16/1817/2019/bg-16-1817-2019.pdf |
| Summary: | <p>The origin and development of the primary autotrophic metabolism on
early Earth were influenced by the two main regimes of degassing of the
Earth – reducing (predominance <span class="inline-formula">CH<sub>4</sub></span>) and oxidative (<span class="inline-formula">CO<sub>2</sub></span>). Among
the existing theories of the autotrophic origin of life in hydrothermal
environments, <span class="inline-formula">CO<sub>2</sub></span> is usually considered to be the carbon source for nascent
autotrophic metabolism. However, the ancestral carbon used in metabolism may
have been derived from <span class="inline-formula">CH<sub>4</sub></span> if the outflow of magma fluid to the surface
of the Earth consisted mainly of methane. In such an environment, the
primary autotrophic metabolic systems had to be methanotrophic. Due to the
absence of molecular oxygen in the Archean conditions, this metabolism would
have been anaerobic; i.e., oxidation of methane must be realized by
inorganic high-potential electron acceptors. In light of the primacy and
prevalence of <span class="inline-formula">CH<sub>4</sub></span>-dependent metabolism in hydrothermal systems of the
ancient Earth, we propose a model of carbon fixation where the methane is
fixed or transformed in a sequence of reactions in an autocatalytic
methane–fumarate cycle. Nitrogen oxides are thermodynamically the most favorable
among possible oxidants of methane; however, even the activity of oxygen
created by mineral buffers of iron in hydrothermal conditions is sufficient
for methanotrophic acetogenesis. The hydrothermal system model is considered
in the form of a phase diagram, which demonstrates the area of redox and <span class="inline-formula"><i>P</i></span>
and <span class="inline-formula"><i>T</i></span> conditions favorable for the development of the primary methanotrophic
metabolism.</p> |
|---|---|
| ISSN: | 1726-4170 1726-4189 |