I found this amidst the roots of a tree I was digging up in my backgarden yesterday. It was relatively near the surface mixed in with the roots, but I live at the top of a hill in the Chilterns, and I am baffled as to how it got there!?
It weighs 170g and measures 6.2x5x4.8cm.
Can anybody help please?
A small explanation as to how it got there would be lovely if anyone has any ideas too.
The specimen is a fossil echinoid (sea urchin).
It would have been within the chalk or the soil covering it (having weathered out of the chalk). As the tree grew, it happened to entwine the echinoid in its roots.
The echinoid itself is composed of flint - much harder and hence persistent than the chalk, hence likely to persist and get caught-up in the roots.
You seem surprised at it being at the top of a hill. That hints at you recognizing it as a fossil sea creature.
Well you are right about what it is. Perhaps the thing to appreciate is that the majority of the sedimentary rocks we see on the surface of the earth were created a very long time ago. Back then, the environment would have been very different, for pretty much whichever part of the planet you consider. The current positions of land and sea as we know them today are largely irrelevant. In the case of the Chiltern chalk, it was laid down 95-65 million years ago, and the area was at that time a warm shallow sea. Since that time, the sediment was buried by a great depth of other sediments, turned to rock, and the rocks as a whole were moved and deformed as a result of such forces as the continents moving about the surface of the earth.Those earth-moving events resulted in the chalk and other strata being raised well above sea level. Later erosion happens to have removed the higher rocks, leaving the chalk exposed at the surface in many places, including hilltops -,just by chance.
I could tell you a bit more about your sea urchin if you gave us a more exact location.
Echinocorys scutata, from the upper chalk. Sea levels were up to around 300m higher than they are today during the depoistation of the chalk group. What we now call the chilterns was situated around the latitude to where you see the Bahamas.