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.
TAGS: Geology, Ammonites