Friday Sprog Blogging: dating.

I do not know why, in December, the Free-Ride offspring turn their attention to questions of evidence and testimony. (I do worry, however, that by this time next year the elder Free-Ride offspring may become a 12-25 truther.) This week, the sprogs considered ways to establish dates that don't rely solely on the testimony of someone who was there.

Younger offspring: I wonder when the first paper airplane was invented.

Dr. Free-Ride: Sometime after the invention of paper, I imagine.

Dr. Free-Ride's better half: Paper was invented a looong time ago.

Elder offspring: By the ancient Egyptians.

Dr. Free-Ride's better half: And how far back do you have to go for a civilization to count as ancient?

Younger offspring: More than fifty years ago.

Elder offspring: My book says the people we call the ancient Egyptians started farming around 8,000 years ago. And we know a lot about ancient Egyptian civilization because they kept written records.

Dr. Free-Ride: That's pretty handy. So, how do we know when those things were written down? Even if they dated the records, they weren't using the same calendar that we do.

Younger offspring: Hmmm.

Elder offspring: Hmmm.

Dr. Free-Ride: I can tell you one way I know about. One of the things that got recorded in ancient Egypt was astronomical observations.

Younger offspring: What?

Elder offspring: Things about where the stars and the planets were in the night sky.

Dr. Free-Ride: Exactly. And since things like planetary motions go in cycles that regularly repeat themselves, you can work backwards from where the planets are now to find the years that could have matched what the Egyptian astronomers observed.

Elder offspring: Sometimes people figure out how old things are -- like pottery or even fossils -- by what layer they're in when a site is excavated.

Younger offspring: Excavated?

Dr. Free-Ride: Dug up.

Younger offspring: Oh.

Dr. Free-Ride: That's true. And there are some other ways to figure out how old things are.

Younger offspring: With a tree, you can count its rings, and the number of rings tells you how many years the tree has been growing.

Elder offspring: There's at least one kind of tree that doesn't grow a ring each year. It lives in Madagascar.

Dr. Free-Ride: I didn't know that.

Younger offspring: Me either.

Dr. Free-Ride: There's another way I know of that you can tell the age of really old stuff that used to be alive. Have either of you heard of carbon dating?

Younger offspring: Does it have to do with going on dates?

Dr. Free-Ride: No. Let's see ... all living things contain a lot of carbon.

Elder offspring: Even bacteria?

Dr. Free-Ride: Yes.

Younger offspring: And fungi?

Dr. Free-Ride: Yes. Also plants.

Elder offspring: And viruses?

Dr. Free-Ride: Look, bub, I'm not going to mix it up with you over whether viruses are alive or not. But they do contain carbon.

Younger offspring: Do I contain carbon?

Dr. Free-Ride: Kid, you're a carbon-based life form, and so is everyone you know and love. It's time to come to grips with that.

Elder offspring: So, what's carbon dating?

Dr. Free-Ride: I'm getting there. If you look at all the carbon atoms in a carbon-based life form, most of them would have atomic weight 12, but there would be a whole bunch that have atomic weight 13 and a whole bunch that have atomic weight 14.

Younger offspring: Some carbons are heavier and some are lighter?

Dr. Free-Ride: Yep. And the heavier carbons and lighter carbons are in a pretty regular proportion to each other when the carbon-based life form that they're in is alive.

Elder offspring: But then?

Dr. Free-Ride: Over time, the heavier carbons are more likely to break down through radioactive decay.

Younger offspring: But not the lighter carbons?

Dr. Free-Ride: No. So what does that mean?

Elder offspring: The older something is, the more of its heavy carbons have broken down?

Dr. Free-Ride: Uh huh. Which means you can look at the proportions of the different kinds of carbons in an old bone or an old piece of wood or an old basket woven from grasses and get a pretty good guess about how old it is.

Younger offspring: That sounds harder than counting tree rings.

Elder offspring: Yeah, but not everything you want to know the age of is a tree.

More like this

A conversation that bubbled up at the dinner table last night, some time after the Free-Ride offspring were informed that the cassoulet they were eating had, as one of its ingredients, white wine. Younger offspring: Why do they call booze "spirits"? Dr. Free-Ride's better half: I think that goes…
Both Free-Ride offspring are charter members of the Order of the Science Scouts Special Children's Auxiliary. They have not, as yet, built their own fire, either in a fire pit or a laboratory. However, a discussion this week about the strange vapor seen emanating from a car's tailpipe one morning…
Yes, it's a day late. Dr. Free-Ride and Dr. Free-Ride's better half are currently engaged in sprog retrieval maneuvers at the home of the Grandparents Who Lurk But Seldom Comment. What follows is this morning's attempt to get the Free-Ride offspring to tell us something science-y. Dr. Free-Ride…
Dr. Free-Ride: So, you know this Friday is Mole Day. Elder offspring: It is? What does that mean exactly? Dr. Free-Ride: Do you remember what a mole is? Not the animal, but the quantity. Elder offspring: Not really. Dr. Free-Ride's better half: It's a convenient unit of measure for things like…

As I understand it, most tropical trees don't have growth rings. Tree rings form because of the differences in growth rates between winter and summer. Since the tropics are a relatively constant temperature all year round, the trees have a near constant growth rate, and thus don't have rings. (Although some places do have rainy/dry seasons, and I think there may be tree rings for those locations.)

> Dr. Free-Ride: Look, bub, I'm not going to mix it up
> with you over whether viruses are alive or not.

I'm not precisely sure why, but this just cracked me up.


Young lady, I must inform you that even at 54 I did not know Gaius Julius Caesar personally.

I must also inform you that the Egyptians did not invent paper. What they used instead is called papyrus. Papyrus is made from a fibrous marsh plant called papyrus. You take some stalks, sort of unroll them, and lay them out on a flat surface. Each layer after the first is laid down with the grain at right angles to the one just below it to give it strength. (Wood has grain. Look for the lines in a piece of wood, the way they go is the wood's grain. Papyrus grain is the way the fibers in the plant's stalk run, which is up and down in a living plant.) Once you have the layers laid out you pound on them a bit with a wooden mallet covered in hide, then put heavy weights on the smushed sheets.

Real paper was invented by the Chinese just a couple of millennia ago, and is made from wood pulp, cotton and linen fibers, and stuff like clay for glossy paper (Mom's scientific journals are printed on glossy paper). Real cheap paper is made mostly from pulp, while the expensive stuff is made from more cotton fiber than any thing else. Paper money is a special type of paper that is more cloth than paper. When you're older, and your hand-eye coordination is much better, you might try calligraphy; which is the art of forming letters using pen and ink real well. Calligraphy uses special pens, special inks, and special papers with a very fine grain and a very smooth texture that like the dollar bill is more cloth than paper. Calligraphy is very much drawing with a continuous line and takes lots of practice.

Now, can you name the paper you can eat?

Coincidentally, it's Nobel Prize winner Willard Libby's 100th birthday on December 17th (not that he's around to celebrate). I'm serving cake at my high school library because he was born in my little town in Colorado.

I know that Alan Kellog is looking for "rice paper" as the answer to "paper you can eat", but that's too narrow an answer now. Paper can be made from potato starch, soy starch, and a lot of other starches now. Chefs have edible menus printed on papers made from such starches. Some cake printers actually can run thin sheets of icing through them, rendering sugar into a sort of "paper".

The domestic and laboratory goddess has a painting of the ancient goddess Isis on papyrus in her office that she obtained during her last trip to Egypt. The paper really is exquisitely well crafted. Plus, you can wash papyrus paper (not that I would wash my painting). It is that much more durable than wood pulp paper. If there is one thing that struck me on our recent trip it's that the Egyptians were amazing engineers.

Glad to know that Duke and I have been firmly categorized (of an ancient civilization > 50 yr. ago). Now if the markets would just right themselves we might be able to retire...

By Super Sally (not verified) on 15 Dec 2008 #permalink