Today, August 14, 2013 is Day 91 of the Papa’s Walk Challenge.

Getting up the hill was a little easier today, and as I came down the hill and walked into the flatlands I was rewarded with the most  stunning sidewalk art!  About 30 concrete panels were covered in chalk drawings in pink, blue, yellow, green, and white.

I stepped gingerly over the artwork, admiring pictures of the sun, rainbows, stars, moons, hearts, people, houses, and palm trees. Plus, there were peace signs throughout the work with words printed in chalk that included “peace,” “love,” “happy,” “mom,” and “sister love.” Those last two words made me think of two young girls – sisters – who spent an afternoon using sidewalk chalk to share their happiness with the world. That just made my day. 🙂

I recalled that Papa used to give me chunks of carpenter’s chalk to draw with on the sidewalk in front of our home. I started wondering about chalk, what it’s made of, and the history of chalk.

On Wikipedia it says, “Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms.”

As I searched a little further, I found a wonderful science essay on the NPR website, Thinking Too Much About Chalk, by Robert Krulwich. He wrote that in the 1860s a British naturalist and evolutionary theorist named Thomas Huxley looked at chalk under a microscope and discovered that chalk is composed of the ancient skeletons of marine life (see picture on left). Krulwich further commented:

“But 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.’  

At one time carpenter’s chalk, as well as blackboard and sidewalk chalk, were composed of natural chalk, but today it’s made from a mineral called gypsum (calcium sulfate).

You can make your own sidewalk chalk – try this DIY recipe from Martha Stewart.