View Full Version : "but **exactly** how do we know how old the earth is?"

06-24-2014, 11:47 PM
So my curious 7th grader asked me this question and now I am in search of resources (preferably documentaries or accessible books). We've watched a few youtube videos together. The one from the Smithsonian was great. But he wants to dig a little deeper and I am coming up empty and I can't get to the library for a couple of days. We're not ready for adult level books on the topic just yet. Hoping for middle school-ish.

does anyone have suggestions? We have done a little earth science and big bang stuff but his questions centre specifically on how we know how old the earth is.
help? please?

06-25-2014, 12:25 AM
There is an episode of Cosmos which answers this exact question. It is to do with the rate at which uranium decays, IIRC. Can't remember which one but look on the website

06-25-2014, 08:34 AM
I was going to suggest Cosmos also. The entire series would probably be enjoyed.

Also, check the Howard Hughes Medical Institute. I found this one, but there may be more (all of their resources are free). Changing Planet: Past, Present, Future | HHMI's BioInteractive (http://www.hhmi.org/biointeractive/changing-planet-past-present-future)

06-25-2014, 09:08 AM
Thanks so much!

06-25-2014, 10:11 AM
I second (third?) Cosmos, we even bought the DVDs.

For more info though I am not sure if you've seen this unit study website (http://www.squidoo.com/chronologicalhistorystudies), crunchymum? It has some good info about the Hadean era, how earth and all the terrestrial planets formed by a process called "core accretion." Cosmos covers this pretty well...the earth was so molten for so long that none of the terrestrial rocks can be easily dated, so smart scientists look to meteorites and date them that way (because they're as old as all the stuff floating around when the earth glommed together). The kid really loved this. Lightbulb moment: "of course!"

There was a blurb recently about how the earth (and moon) might be slightly older than thought (http://www.iflscience.com/space/earth-and-moon-are-60-million-years-older-previously-believed). Interesting that it's a moving target...shows there's so much more to know!

06-25-2014, 10:12 AM
while its not quite that exact question, this video does a great job of showing the process scientists go through to determine similar questions - and it free (we managed to get a free dvd of it). Looks like they even have additional resources with it, too (the material is all on the right-hand box, which took me a minute, not at the bottom of the page) you can download the movie or watch it on youtube

The Day the Mesozoic Died | HHMI's BioInteractive (http://www.hhmi.org/biointeractive/day-mesozoic-died)

Their whole website is great, but this is one of the more kid-accessible ones, I think.

06-25-2014, 10:57 AM
Another option is Bill Bryson's book A SHort History of Nearly Everything (and I believe there's a version for kids/younger people), too. It's less technical, but it does go through how scientific knowledge progressed from believing the earth was a few thousand years old to the billions now understood. He's a great writer (if you haven't previously read his stuff) and it also has interesting material about many of the people themselves. He has a knack for painting vivid pictures of people!