What do they claim?
TNA 4 explains that the nuclear fusion in the Sun's core would have been weaker leading to a Sun that was 25% fainter 3.5 billion years ago. This decreased luminescence would lead to a temperature on Earth that was below freezing during the time that life was beginning to form on Earth. TNA 4 allows that scientists have proposed several solutions including increased greenhouse gas levels in the atmosphere, but claims that there is no evidence for this and that there is no way that the greenhouse gas levels and the sun's luminosity could change in sync.
Where's the problem?
This explanation is a great example of a YEC propaganda trick I think of as "Tell the truth, just not the whole truth." I'm going to recopy the previous paragraph and underline all of the true statements in the paragraph. I'm also going to bold a true statement that TNA 4 hoped you missed.
TNA 4 explains that the nuclear fusion in the Sun's core would have been weaker leading to a Sun that was 25% fainter 3.5 billion years ago. This decreased luminescence would lead to a temperature on Earth that was below freezing during the time that life was beginning to form on Earth. TNA 4 allows that scientists have proposed several solutions including increased greenhouse gas levels in the atmosphere, but claims that there is no evidence for this and that there is no way that the greenhouse gas levels and the sun's luminosity could change in sync.
The vast majority of what is in TNA 4 for this section is true, but incomplete.
What does science really say?
The Faint Young Sun Paradox was proposed by Carl Sagan and George Mullen in 1972. They were bringing up a good point - the Sun was warming the Earth so much less that the Earth should have been frozen 2.3 billion years ago. However, even as they brought this up, the proposed one of the current solutions.
From the abstract published in Science (an very prestigious and selective journal), they state "Solar evolution implies, for contemporary albedos and atmospheric composition, global mean temperatures below the freezing point of seawater less than 2.3 aeons ago, contrary to geologic and paleontological evidence."
Two important points:
- Sagan and Mullen did the math based on current albedos (reflectiveness of the Earth's surface) and the percentage and characteristics of gases found in the atmosphere now. They never state that the albedo or atmosphere characteristics were unchanging; in fact, they demonstrate how adding some greenhouse gases at certain points removes the problem.
- Sagan and Mullen imply that the geologic and paleontological record - which was solid in 1972 and has advanced mightily since then - show that the Earth wasn't freezing 2.3 billion years ago.
That's where the "several solutions" come into play.
1) The atmosphere was different. Scientists have neat tricks for capturing tiny gas bubbles trapped in ancient zircons to get an idea of what gases were present and in what amounts. Scientists aren't exactly sure of the atmospheric composition, but there was more than enough carbon dioxide to wrap the Earth in a greenhouse effect atmosphere.
2) The Earth was still cooling down from formation and heat generated by radioactive decay. Again, scientists are currently working out the details from age of zircons, but the Earth itself was releasing more heat 3 to 4 billion years ago than it is today.
3) The planet as a whole was darker colored leading to better capture of heat and had fewer clouds. The darker color came from the fact that the continents were in the process of forming. Continental rocks are lighter in color than the oceans so a world with more oceans captured sunlight more efficiently. The fewer clouds idea is based on the fact that most clouds form around biological nuclei that allow water to condense. Since life was just getting started, there were fewer nuclei and fewer clouds.
These solutions may work together as well. The warmer Earth could have heat captured from the Sun more effectively by the oceans and both sources of heat were better maintained by an atmosphere with more greenhouse gases.
What about the intricate interplay of solar luminosity and greenhouse gases brought up by TNA 4?
Strawman. No one - well, outside of YEC - has claimed that solar luminosity and greenhouse gases moved in perfect sync. Changes in the rock cycle and plate tectonics eventually dropped the amount of carbon dioxide in the atmosphere. Meanwhile, the Sun's fusion power got stronger and stronger. The two are correlated in a vague way but there is no causation that I've seen evidence of.
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