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In hindsight, both theories were deeply misguided, for similar reasons.
They assumed that current rates—of sediment deposition and of salt transport by rivers—were the same as historical rates, despite the evidence they had that our own age is one of atypically high geologic activity. The rock cycle, as we now know, is driven by plate tectonics, with sedimentary material vanishing into subduction zones.
One outstanding feature of this drama is the role played by those who themselves were not, or not exclusively, geologists.
Most notable is William Thomson, ennobled to become Lord Kelvin in 1892, whose theories make up an entire section of this collection.
The first of these referred to the rate of heat loss from the earth and the length of time it would have taken to form its solid crust.
The second referred to such topics as the detailed shape of the earth (bulging slightly at the equator) and the dynamics of the earth-moon system.
The Talmudic rabbis, Martin Luther and others used the biblical account to extrapolate back from known history and came up with rather similar estimates for when the earth came into being.
The most famous came in 1654, when Archbishop James Ussher of Ireland offered the date of 4004 B. Within decades observation began overtaking such thinking.
The first argument was completely undermined after taking into account the amount of heat generated by radioactive decay.We, of course, know the final outcome, but we should not let that influence our appreciation of the story as it unfolds.Even less should we let that knowledge influence our judgment of the players, acting as they did in their own time, constrained by the concepts and data then available.By 1788 Hutton had formulated a theory of cyclic deposition and uplift, with the earth indefinitely old, showing “no vestige of a beginning—no prospect of an end.” Hutton considered the present to be the key to the past, with geologic processes driven by the same forces as those we can see at work today.This position came to be known as uniformitarianism, but within it we must distinguish between uniformity of natural law (which nearly all of us would accept) and the increasingly questionable assumptions of uniformity of process, uniformity of rate and uniformity of outcome.