From your toothpaste, to the classroom, to road construction, chalk is a material we use more than we realize. These white hills are all chalk. But where does it come from?👉Planktonic microfossils.
Plank-what?
Chalk is a type of limestone that originated from a type of marine phytoplankton (“microscopic plants”). Mainly, coccolithophores.
Back in the time of the dinosaurs, these microorganisms absorbed CO2 from the atmosphere and with other minerals (i.e. calcium) they protected themselves by creating an external skeleton of calcium carbonate (CaCO3 – limestone). When they died, they formed part of the “marine snow” that falls and accumulates at the bottom.
All this, by the way, still happens today.
For many years we had this accumulation of coccolithophores under the sea in relatively shallow areas. In fact, if it had been deeper – due to increased pressure – it could have turned into marble.
Almost alongside the meteorite and weather conditions of 65 My ago, the tectonic plates were already moving towards the continental formation we know today. As the African and Eurasian plates began to collide, along with changes in sea level, these chalk hills as we know them today began to appear out of the water.
So if you go for a walk there, you’re literally walking on top of layers of microfossils of coccolithophores accumulated over millions of years. Just don’t get too close to the border!
Have you been there already?
Recommended read:
Müller, M.N. 2019. On the Genesis and Funciton of Coccolithophore Calcification. Frontiers in Marine Science.
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