The Young Faint Sun Paradox

Because I'm such a whacko ("kook" is much too mild a term), I've been reading some Young Earth Creationist arguments. I don't know if they are any good, but they are interesting. For example:

The Young Faint Sun Paradox and the Age of the Solar System:

"According to theory, the Sun derives energy by the thermonuclear conversion of hydrogen into helium, deep inside its core. There is convincing evidence that the Sun is getting at least half of its energy by this method. Such a thermonuclear source could power the Sun for nearly 10 billion years. Most scientists think that the Sun (along with the rest of the solar system) is about 4.6 billion years old, which means it would have exhausted approximately half its ‘life’.

Over the Sun’s lifetime, the thermonuclear reactions would, according to theory, gradually change the composition of the core of the Sun and alter the Sun’s overall physical structure. Because of this process, the Sun would gradually grow brighter with age. Thus, if the Sun is indeed 4.6 billion years old, it should have brightened by nearly 40% over this time.1

Evolutionists maintain that life appeared on the Earth around 3.8 billion years ago. Since then, the Sun would have brightened about 25%,2 though there is some uncertainty in that figure.3 This would appear to present a temperature problem for the evolution of life and the Earth. With the current hand-wringing over global warming, one would expect that such a large difference in the solar output would have greatly increased the Earth’s temperature over billions of years. Yet most biologists and geologists believe that the Earth has experienced a nearly constant average temperature over the past 4.6 billion years, with perhaps warmer conditions prevailing early on.4 The problem of how the Sun could have increased in brightness while the Earth maintained a constant temperature is called the ‘early faint Sun paradox’.

Just how great is the problem? A simple calculation can be made assuming that, over time, there has been no change in the Earth’s reflectivity or the ability of the Earth to radiate heat. While this approach is almost certainly unrealistic, it is useful to illustrate the problem. With these assumptions, we find that a 25% increase in solar luminosity increases the average temperature of the Earth by about 18°C. Since the current average temperature of the Earth is 15°C, the average temperature of the Earth 3.8 billion years ago would have been below freezing (-3°C). Thus when life supposedly was just beginning, much of the Earth would have been frozen."