# Effects of primitive photosynthesis on Earth's early climate system

## TL;DR

This study models how primitive, oxygen-free photosynthesis could have significantly influenced Earth's early climate by amplifying methane cycles and expanding conditions for warmth, highlighting complex biosphere-atmosphere feedbacks.

## Contribution

It introduces a biogeochemical model demonstrating the impact of primitive photosynthesis on early Earth's climate and expands understanding of biosphere-atmosphere interactions in anoxic conditions.

## Key findings

- Primitive photosynthesis could amplify methane cycles.
- Hybrid ecosystems broaden warm climate conditions.
- Early climate was regulated by feedbacks linking biosphere and geochemical cycles.

## Abstract

The evolution of different forms of photosynthetic life has profoundly altered the activity level of the biosphere, radically reshaping the composition of Earth's oceans and atmosphere over time. However, the mechanistic impacts of a primitive photosynthetic biosphere on Earth's early atmospheric chemistry and climate are poorly understood. Here, we use a global redox balance model to explore the biogeochemical and climatological effects of different forms of primitive photosynthesis. We find that a hybrid ecosystem of H2-based and Fe-based anoxygenic photoautotrophs - organisms that perform photosynthesis without producing oxygen - gives rise to a strong nonlinear amplification of Earth's methane (CH4) cycle, and would thus have represented a critical component of Earth's early climate system before the advent of oxygenic photosynthesis. Using a Monte Carlo approach, we find that a hybrid photosynthetic biosphere widens the range of geochemical conditions that allow for warm climate states well beyond either of these metabolic processes acting in isolation. Our results imply that Earth's early climate was governed by a novel and poorly explored set of regulatory feedbacks linking the anoxic biosphere and the coupled H, C and Fe cycles. We suggest that similar processes should be considered when assessing the potential for sustained habitability on Earth-like planets with reducing atmospheres.

---
Source: https://tomesphere.com/paper/1907.12995