Plate Tectonics, Ammonites, Caterpillars

Plate Tectonics

The rocks at the bottom of the ocean tend to be younger than the rocks on the land masses. This is because the plates which form the earth's crush are pulling apart, and new rock forms between. At the boundaries of these plates, three different things can happen. These are constructive, destructive, and conservative.

Constructive

This is when the plates pull apart and new rock is formed between them. Here, in some rocks, the changing magnetic field of the earth can be seen as in some places in ocean rocks where the field points north and in others it points south in a symmetrical pattern around the fault line.

Destructive

In other places, rocks are destroyed as plates push against each other, and one is buried under the other.

Conservative

This is when plates slide along each other. An example of where this happens is on the west coast of the USA where the Pacific plate slides alongside the North American plate at the San Andreas Fault.

Ammonites

Today I bought a cross section of an ammonite. It's at least 75 million years old. Let that sink in. 75 million years. This beautiful spiral shell once housed a squid-like creature which lived only in the outer chamber. Maybe this is the shell it died in, or perhaps it shed it and became one of the metre wide ones before finally expiring.

Caterpillars and Trees

In our walk today at Kingsbury Waterpark, we saw some strange lines hanging down across the road. They were white with wider black sections. When we got closer we saw that this black sections were hordes of caterpillars hanging in groups from threads from the trees above. The trees were covered in white webs, with very few leaves left. A quick google informs me that these are the caterpillars of ermine moths. I think they are spindle ermine moths which grow on the spindle tree. Spindle trees are so named because their wood used to be used to make spindles for spinning.