Hiatus: Some Geological Truths May Never Be Known...

A hiatus in geology is a significant interval of time where there is no rock record in an area. The boundary between the two beds is called an unconformity. Here a granite deposited 1,100 million years ago is directly touching a 500 million sandstone.  This unconformity represents a 600 million year hiatus.

Sometimes in geology we're very lucky and the right "recipe" leads to amazing insights into a period of time.

The Burgess Shale is a great example. Strange, soft animals living more than 500 million years ago were suddenly buried under a sheet of fine mud. The mud kept away scavengers and oxygen, locking the animals away like mummies in a tomb. Half a billion years of lucky chances lead these fossils to survive erosion and tectonic activity, leaving the exquisitely preserved remains to be discovered in Canada in 1909. It is an amazing snapshot of some of the earliest complex animals on Earth.

But usually we're not so lucky.

Sometimes rocks are destroyed or altered by the squeezing forces and heat that move continents, turning sandstone and shale into quartzite* and schist. Sometimes wind, ice and water scour away any trace of the rock. Sometimes the rock is never deposited at all.

We don't always know what causes a hiatus - a gap in the time represented in the rock record. Like a cut in video footage it can skew our interpretations of events.

But I have always loved the idea of a hiatus because it means that we not only don't know everything, we literally can't know everything. There will always be some mystery.

My favorite quote on the idea of hiatus comes from Darwin's "On the Origin of Species":

"For my part, following out Lyell's metaphor, I look at the natural geological record, as a history of the world imperfectly kept, and written in a changing dialect; of this history we possess the last volume alone, relating only to two or three countries. Of this volume, only here and there a short chapter has been preserved; and of each page, only here and there a few lines. Each word of the slowly-changing language, in which the history is supposed to be written, being more or less different in the interrupted succession of chapters, may represent the apparently abruptly changed forms of life, entombed in our consecutive, but widely separated formations." - Charles Darwin, On the Origin of Species

*Pro tip: play "quartzite" on a triple word in Scrabble and your opponent will never know what hit him!

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