In the 1860s, the naturalist (advocate of evolutionary theory) Thomas Huxley looked at chalk under a microscope. Here's what he found, according to Robert Krulwich:
Chalk is composed of extremely small white globules. They look, up close, like snowballs made from brittle paper plates. Those plates, it turns out, are part of ancient skeletons that once belonged to roundish little critters that lived and floated in the sea, captured a little sunshine and carbon, then died and sank to the bottom. There still are trillions of them floating about in the oceans today, sucking up carbon dioxide, pocketing the carbon. Over the millennia, so many have died and plopped on top of each other, the weight of them and the water above has pressed them into a white blanket of rock, entirely composed of teeny skeletons. Scientists call these ancient plates "coccoliths." Technically, they are single-celled phytoplankton algae.
That's really amazing:
I'm charmed by the idea that when a school teacher writes her name on a blackboard on the first day of class, what she's really doing is crushing the skeletons of terribly ancient earthlings into a form that spells out the name "Mrs. Guttenheimer." Does she know? Thomas Huxley thinks she should.
Whoever knows the true history of chalk, he told the workers at Norwich, will have "a truer, and therefore a better, conception of this wonderful universe."