If you were able to dive in a submersible on the continental shelf in the ocean that used to cover much of southern Europe in water depths between 50 and 150m you would see reefs that looked a lot like the sponge reefs we see today on the BC shelf. The seabed in these areas would have been carbonate (limestone) or marl - that is a limestone with some mud added. The time of greatest distribution of the glass sponge reefs was the late Jurassic - about 145 million years ago. The ocean covering this part of the world was known as the Tethys and in the Jurassic the continents looked quite different. Abundant organisms from that period were many species of Ammonites, which are often found in the fossilized sponge reef rock formations, and marine reptiles such as pleisiosaurs that also swam in the late Jurassic seas.

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