Wednesday, March 28, 2007

Prehistoric Sidewalk

Last weekend, I decided to have a break, and visited friends who have a house in France and had invited me since long to join them there. So, I took off Thursday and Friday, and enjoyed the wonderful mild weather of early sprintime with my friends, mostly hiking and walking. The landscape around their place is just great, but what was most fascinating to me: You can literally walk over fossil remains of million years ago!

What looks like simple, terrace-like sheets of rocks in a small grove, at closer inspection, turns out to be a former seabed!

Can you spot it? There it is, next to the centre of the photo, the petrified shell of an ammonite! This is what you see when you take a closer look:

As every self-respecting amateur geologists would do, I put a hammer next to the fossil to better convey its size. This special specimen had been spotted by someone else before, who also had cleaned the spot a little bit. Wolfgang, my friend, was lucky and found another one some twenty metres away, which we could dig out using the hammer.

Our geological map told us that this spot shows rocks form the apto-albian period in the Lower/Early Cretaceous, in the time of the dionosaurs. They are called marnes bleus, or marls, and can contain quite large ammonites. They are about 100 million years old!

It is really hard to get a feeling for this enormous span of time - this nice interactive explorer of Deep Time may be a start.

When I came back, I learned from a report on BBC and the Scientific American about paper in Science just from last week, that I could walk over rocks about 40 times older! All I have to do is travel to Greenland. Some volcanic rocks there are now the oldest known rocks on the Earth's surface - more than 3.8 billion years old.

Update: There is a nice post about Geological Basics: the difference between chronology and stratigraphy at Highly Allochthonous, with a scheme of the different geological series that make up the geological timescale.



  1. That's awe-mazing!

    But anyway, we KNOW that the Earth is only ~6000 years old! ;-)

  2. with a gamma factor of 10^6 things can look very differently. maybe the bible was just written in a different reference frame. everything is relative.

  3. The bible is both literal and incorruptible. Scrambling the letters does not degrade the meaning,
    The Anagrammed Bible

    OTOH, like Aristotle and Scientific Socialism, it's empirical crap. Empirical reality offers lethal comments to those who walk a different path. Priests and politicians know the truth: "Hodie mihi, cras tibi."

    String theory currently straddles the line.

  4. I'd never thought of that, Bee. I always figured that the Bible has truth to about the extent that the stories my parents told me when I was a child had truth.

    That is, when human society was very young, it would be a disservice to give them, for example, the knowledge of how to make atom bombs. We were lucky enough as it was to have the invention only used twice.

  5. with a gamma factor of 10^6 things can look very differently


    But 10^6 is an enormous gamma factor... And yet, it is the factor to go from 6000 years to 6 billion years.. I mean, that's elementary arithmetics we have all learned in school, but nevertheless, it's hard to really grasp these big numbers..

    BTW, inspired by the ammonites, I 've dug up a nice little book by Stephen Jay Gould from my shelves, which I wanted to read since quite a long time. The book tells the story of people like Hutton and Lyell, who in the 18th and 19th century first became aware of the huge timespans of geological processes and the history of the Earth. It's a fascinating reading.

    It compares the importance of this discovery of "deep time" to Copernicus. And indeed, the idea of a "short" history of 6000 years is probably as "natural" as the idea that the sky with the planets and stars is made up of several spheres around Earth, and not so big and empty as we know today that it is...

  6. I like artifacts of cultures that existed. Rock paintings. Medicine Wheels.

    I imagine standing there in the picture, it would seem strange that one could perceive it as the bottom of some ocean?

  7. What is the name of the place you visited in France?

  8. Hi lobachevsky,

    the place is close to Sisteron, between the Provence and the Dauphiné. It's not especially famous for fossils - it seem that you can find ammonites at many places, when you know where to look for them.


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