Early Earth Stuff

[lpetrich]

Meteorites reveal high carbon dioxide levels on early Earth | Penn State University

Iron micrometeorites found in ancient soils suggest carbon dioxide made up 25 to 50 percent of Earth’s atmosphere 2.7 billion years ago, and that pressure at sea level may have been lower than today, Penn State researchers said.

...
Those levels of carbon dioxide would suggest a warm planet, but other climate evidence finds Earth was cool at the time and partly covered by glaciers. Lower nitrogen levels resulting in lower pressure would allow for both high carbon dioxide levels and cool conditions.

“There are data, referenced in our paper, that support lower nitrogen concentrations during this time,” said Jim Kasting, Evan Pugh University Professor in the Department of Geosciences at Penn State and Payne’s adviser. “Our study of micrometeorite oxidation falls in line with that interpretation. The possibility that our major atmospheric gas, nitrogen, was less abundant in the distant past is really intriguing.”

Microbe lasagna tells us about what life was like billions of years ago – Sciworthy - very disappointing. Gives a lot of very elementary background on stromatolites, that microbe lasagna.

Early Microbial Ecosystems - 2002 Report

We investigate cyanobacterial mat ecosystems that have ancestors extending back billions of years. These mats allow us to examine microbiota and ecological processes that participated in early evolution, modified the early environment and created biosignatures.

Mentions oxic vs. sulfate respiration -- sulfate as an oxidizer. Also mentions release of H2 into the atmosphere as a form of respiration -- breakdown of biological molecules for energy.

Lipid biomarker and phylogenetic analyses to reveal archaeal biodiversity and distribution in hypersaline microbial mat and underlying sediment - JAHNKE - 2008 - Geobiology - Wiley Online Library -- "This study has utilized the tools of lipid biomarker chemistry and molecular phylogenetic analyses to assess the archaeal contribution to diversity and abundance within a microbial mat and underlying sediment from a hypersaline lagoon in Baja California." -- about 1-4% of biomass.

Stromatolites can have complicated ecologies, with several kinds of microbes in them living off of the primary producers in them.

 

[lpetrich]

Earth during a Faint Young Sun | News | Astrobiology

Research supported in part by the NASA Astrobiology Program provides new insight into the ‘faint young Sun problem.’ The ‘faint young Sun’ concept refers to a time during the first billion years of Earth’s history, when liquid water was present at the planet’s surface but output from the Sun was only seventy percent of what it is today. Scientists have long been trying to understand how the planet remained warm enough for liquid water when the Sun was providing significantly less energy to the Earth’s surface. The new study examines the potential role of the carbon-silicate cycle in stabilizing Earth’s early climate.

noting
Probable Cold and Alkaline Surface Environment of the Hadean Earth Caused by Impact Ejecta Weathering - Kadoya - 2020 - Geochemistry, Geophysics, Geosystems - Wiley Online Library

The Earth's environment during the Hadean eon, 4.5 to 4 billion years ago, is obscured by a lack of geological evidence. However, life likely arose then, so improving our knowledge of the early environment is essential for understanding the origin and evolution of life. Here, we build a geological carbon cycle model that simulates the early surface environment and generates probability distributions for the level of atmospheric carbon dioxide (CO2), average surface temperature, and ocean pH over time. During the Hadean, CO2 dissolved in water is consumed by reacting with material ejected from meteorite impacts, so CO2 levels tend to be low and the greenhouse effect weak. The consequences are low surface temperature and alkaline seawater. The probability that the surface temperature was lower than the freezing point of water and that seawater pH exceeded 7 is 70% at 4.3 billion years ago. Thus, if life began in the Hadean, it likely emerged in a cold global environment, and early life may have spread into an alkaline ocean.

In more detail,

log10(p(CO2) in bar) = -2.21+3.01-2.54
T = 259.2+84.1-14.4 K
pH = 7.90+1.21-1.60
(2 standard deviations)

The error bars are too big to provide definite conclusions.
So the stated conclusions do not seem very strong.