Tag Archives: relative time

Marrying Fossils, Isotopes and Geological time

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Aportion of William Smith's wonderful geology map of England, Wales and Scotland

Fossils and Strata; Relative geological time

When one sedimentary layer overlies another, we can be fairly certain that the lowermost is the older of the two.  The important step of codifying this relationship in a set of rules was taken up by Nicholas Steno in 1669 (the Law of Superposition). Although fairly obvious now, this was an important intellectual step in understanding what we now call relative time; that things, especially sedimentary strata, are older or younger than other strata.  This is the essence of the science we call stratigraphy. Continue reading

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How do we know which way is up? #1. Getting started

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How Geologists Interpret Ancient Environments. 1 Getting started

You are confronted with rock formations that might look something like this…

Folded sandstone exposed on a ridge - great place to examine the rocks

The local geologist tells you that the rocks you see here originally were deposited as sands and muds in shallow seas, where beaches and broad coastal tidal flats passed seawards to deeper waters, and landwards to marshes and scrubby coastal plains across which rivers and streams coursed. How did our geologist figure this out? What is it that geologists see in the rocks that help them paint this picture of an idyllic world that existed so many millions of years ago – a world beyond memory, where, in a different eon, a summer cottage would have been rather nice. Continue reading

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