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When James Hutton in 1785 presented to the Royal Society of Edinburgh his ideas on the uniformity of earth processes (over vast tracts of time), he did so with both feet planted firmly on good Scottish ground. Hutton’s Principle, for which Archibald Geikie later (1905) coined the phrase “The present is the key to the past” gave to geologists a kind of warrant to interpret the geological past using observations and experiments of processes we see in action today (see an earlier post for a bit more discussion on this philosophy). One wonders whether either of these gentlemen gave thought to the Principle being used to interpret processes elsewhere in our solar system.
There is of course, no logical reason why we cannot use terrestrial environments and physical-chemical-biological processes to unravel the geology on our solar neighbours. We may need to extend our thinking beyond purely earth-bound processes, but the Principle remains a starting point for scientific thinking, interpretation, and discovery. Mars provides the perfect opportunity for this scientific adventure. Continue reading →
How Geologists Interpret Ancient Environments. 6 The value of missing time
When you next look at sedimentary strata exposed in a hillside, cliff or road-cut, don’t just think of it as a pile of rock but as an expression of time; the length of time it took to deposit all that sediment. The mountain exposure in the accompanying image is a great example. Here, thousands of sedimentary layers, or strata accumulated one at a time, one upon the other. Geologists tend to think of a succession like this as representing relatively continuous deposition of sediment, not necessarily uniform, but certainly continuous. However, we also recognize that between each stratum there is probably some missing time that represents the amount of time taken to change from one set of environmental conditions to another. For example, one layer may have been deposited as beach sand and the overlying layer in an estuary or tidal channel. The length of time that is missing may be minutes, weeks, 100s or even 1000s of years that, from a geological perspective are like the blink of an eye. Continue reading →