Geological Time

Posted: May 18, 2013 in Chat
Tags: , ,

1

Current estimates on the Grand Canyon suggest that the Colorado River has been gouging its way through the Colorado bedrock for about 17 million years.

The position now is that with the uplifting of the plateau the river has been able to cut down through nearly 2 billion years’ worth of rock strata.

 

That means that sediment has been laid down there for more than 2 billion years; that the area was a fairly level, fairly stable sea or lake bed for that time.

It means that the sediment has been weathered from neighbouring rock formations, then washed down there, laid down there, built up over, over that amount of time.

It means that previous rock formations existed there, and were weathered down. Which means those previous rock formations were uplifted rocks before the weathering began.

 

It means the sediment was fossilized by tremendous weight , creating frictional heat bonding the sediment together, to form rock minerals and crystals. To create a rock landscape.

And it also means that this fairly level, stable area has also been uplifted to its current height above the plain.

 

2

The time scale is phenomenal – how can we begin to imagine that length of time? And the energies needed to uplift that weight of rock – greater than any earthquake or volcanic activity we have ever known.

 

It is estimated that 25 to 30 million years ago the ape -monkey-man split occurred. This was around the time the great African Rift Valley… rifted. Previously to this it was a fairly level sedimentary plain. The rock layers crumpled and pulled apart. The upper region of this rift can still be seen and active on the Somali/Red Sea coast.

 

It is estimated that plate tectonics, which accounts for all this rifting and lifting, has been going on for about 3 billion years. It has also been estimated the most active tectonic period was about 1.1 billion years ago; after which it has slowed down as the earth cooled, as the plates became thicker, heavier.

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Comments
  1. liminal city says:

    Great post. The enormity of it all weighs heavy on our species.

  2. Gee thanks.
    Ironically this posting was all in a bit of a rush – meant to do more on time scale mentioned and likely plate-tectonic positions, but… time is a tricky beldame at times.

  3. Malou says:

    My husband who is a geologist always point out to me that the decades and centuries that seem like forever when we reckon time is pittance from a geological time scale. When we were at the Grand Canyon many years ago, he explained that this geological wonder is the best way to see the earth and its history with the naked eye.

  4. This is excellent Malou: I am only writing from a desk top, I have never been there!
    We do take so much for granted; I wonder at times whether the subject of Geological Time is going to be the next Big Thing in the public mind.

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