The faint sun problem

The early history of our planet poses many scientific conundrums, for creationists as well as for the orthodox view. The following list is a sample:

• Why are there no rocks dating to the first 700 million years of Earth's history (called the Hadean)? All that remains from that time are tiny, rare, zircon crystals.

• Those crystals tell us that there was abundant water on the primeval Earth. Where did the water come from?

• Towards the end of the Hadean the Earth-Moon system was bombarded by asteroids. Nearly all the craters on the Moon formed in this event and some are hundreds of miles in diameter. Most of the Earth's oceans would have evaporated as a result of the energy released, yet the oldest rocks on Earth, immediately after this cataclysm, show that water was everywhere.

• When and how did the first forms of life evolve into existence? Credible explanations for the 'origin of life' still elude us, and the earliest evidence is controversial.

• Since there were oceans from 3.9 to at least 1.8 billion years ago, why were they not frozen over? According to astronomers, the Sun 3.9 billion years ago radiated only 75% of the heat it gives out today.

• Why were the oceans throughout that time not only not cold, but much warmer than today?

Some of these points are discussed on the website Earth History: A New Approach. Here we will just say a little about the last two.

The first of these is known as 'the faint young sun problem' (or 'paradox' as some call it). According to current ideas about how stars evolve, stars with the same mass as the Sun's gradually become warmer and brighter. At the time of the oldest rocks the Earth's oceans would have been frozen over, and would have remained so for much of its history.

We know from geological evidence, however, that the Earth was not frozen over. So how do we resolve the problem? One approach is to look for some 'fix', such as the hypothesis that there was much more methane or carbon dioxide in the atmosphere then than we previously supposed, and that this created a greenhouse effect. Such proposals have problems of their own, however. Another approach is to question whether the Sun is billions of years old. But this too is not satisfactory, for, just as there is good evidence that a lot of radioactive decay has taken place on Earth (see An Earth billions of years old?), there is also good evidence that a lot of hydrogen-burning has taken place in the Sun, in keeping with the idea of a faint early Sun. Thus, while disagreeing about the age (i.e. the rate at which hydrogen was burned) we accept that the Sun is likely to have once been 25% cooler than now.

Or a non-problem?

There is a problem, however, only if the Earth is billions of years old. If instead rates of radioactive decay were faster in the past, then the Earth’s interior would have been considerably hotter, and having reached its peak, it would then have started to cool. With a more molten, fluid and convective interior, the rate of seafloor spreading at the mid-ocean ridges would also have been faster. This is indeed one of the main ways in which the Earth has lost its internal heat: seafloor spreading is like the sweating of a body in hot weather. Although cooler than in the past, the Earth is still losing more heat than it generates – supposedly after 4.6 billion years!

Thus, early on, the biosphere did not need as much heat from the Sun. It was sufficiently well insulated by the atmosphere, and faster rates of seafloor spreading kept the oceans warm – warmer than today.

Recolonisation theory predicts high ocean temperatures after the asteroid storm that terminated the Hadean. Although water flooding up from under the original land counteracted the heat energy of the impacts, the new oceans were still very warm, and continued to be warm for thousands of years – well into the Proterozoic (2.5 to 0.54 billion years ago) – because of the very high rates of ocean crust formation. In the vicinity of the spreading centres marine temperatures could have been in excess of 60-70° C. For a long time, prokaryotes (archaea and bacteria) are likely to have been the only kinds of organism that could have flourished and made a mark on the geological record.

High ocean temperatures would also account for the evidence of very low levels of atmospheric oxygen during the Archaean and Proterozoic. Most of the evidence comes from marine deposits. Although these show extremely small amounts of oxygen in the surrounding water, the solubility of oxygen decreases as water temperature increases. Marine sediments may therefore not be a reliable indicator of oxygen levels in the atmosphere.