Deep Time and Uniformitarianism

Deep time was discovered by James Hutton on a scientific basis in 1788. However, deep time became deeper since then we know now the earth is older than 4.5 Ga. Since that time, our earth has been cooling considerably. In the Archean the heat flow out of our earth was 6 times more than today. That means strict uniformitarianism cannot be applied for the entire earth history. The question becomes whether the fundamental processes on earth have changed in any fundamental way. Things we do not have actualist examples of the Archean environments today, these forces are to resort to the first principles of physics and chemistry. We have to ask ourselves what mechanism may have dominated heat loss of the planet in the Archaean and the early Proterozoic that governed the tectonic regime of the earth. What mechanism has governed the tectonic regime of the earth in the Archean and the early Proterozoic? The most efficient way is to lose heat with convection. Therefore, we can assume that the convection has always dominated terrestrial tectonics. However, there is a problem; in the Archean the mafic crust was thicker, but the lithosphere was thinner. This arises a doubt whether the subduction was possible under such circumstances. Geochemical work showed that wet melting was going on the earliest Archean. This indicates some sort of subduction must have been going on. On Venus, shortening amounts of hundred kilometers or more in the margins of the Tesserae seems to be accomplished by the décollement folding and thrusting. Then the question is what happened to the underthrust crust? Similar process on early earth may have produced wet melting by transporting ocean water in to the earth’s mantle. This tells us that plate tectonics must have been operative since the earliest time on earth. However, at the time spreading centres and subduction zones must have been much longer than they are today at consequently plates were slower. Continent grow by smashing island arcs against one another including their large subduction accretionary complexes. The principal task in deep earth research today is to be able to track the transition from the tectonics of the very hot earth to the present one.