Coccolithophores are unicellular marine algae, just a few microns in diameter. They make up for their small size by their abundance: it’s estimated that they dump around 1.4 billion kg of calcite every year into the world’s oceans. This comes from their microscopic plates of calcite, called coccoliths, that once formed exoskeletons (‘coccospheres’) around them. The North and South Downs are chalky white because they’re largely made up of coccoliths. Coccolithophres have been around since at least the Late Triassic, over 200 million years ago, and are still active. Here, one explains:
I’m an armour-plated alga,
Once something’s tried to eat me,
It won’t come back for more!*
We can’t see what we’re doing
’Cos we haven’t any eyes,
So we don’t eat other creatures –
My coccolithic coat
Of calcite plates I made;
But when I die, they’ll be
On the ocean floor arrayed.
My ancestors did likewise,
Their plates make up the Chalk:
You’re treading on their armour
When you take a Downland walk.
Although we are so tiny,
We’re useful carbon stores.
We don’t need lots of nutrients,
As we drift from place to place,
But when we get together
We’re visible from space!
- This might be wishful thinking, according to the results of a 2017 study reported by Suzanne Strom and others at Shannon Point Marine Center, Washington University.
See also Chalk talk.