Tag Archives: sedimentary environments

Astronomy, Cycles and Climate Change

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Cycle: ( noun) A series of events that are regularly repeated in the same order (Oxford Dictionary)

 

Jurassic conglomerate cycles - how did they form?

How Milankovitch cycles effect Earth’s climate

Natural cycles are all around us; tides, seasons, sun spots, birthdays, El Niño.  In geology we can identify cycles at many different scales, from the really grand to the wafer-thin (deference to Monty Python), from those that span eons, to cycles that repeat every few seconds.  Perhaps the grandest of earth cycles are those that last 100-300 million years and involve the formation and destruction of tectonic plates.  On a more human time scale there is the seemingly never-ending train of waves rushing to meet you on your favourite beach. Continue reading

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The Ancient Earth 7. The Art of the Stromatolite

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Algae, Fossil Slime and Organic Precambrian Art

Stromatolites are the earliest physical life forms on earth; they were the precursors to pretty well everything you see living today. There may be indications of earlier life forms preserved as chemical signatures, but as fossils go, something you can see and touch, stromatolites are it. The oldest stromatolites known are from Western Australia – about 3400 million years old. These ancient structures were built by primitive algae and bacteria, aka cyanobacteria, sometimes referred to as blue-green algae. Clearly life had already evolved to something quite complex by 3400 million years ago.

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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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