From my facebook feed.
It’s been recently reported that 4 out of 10 Americans believes the earth is around 10,000 years old.
I can sympathize with this belief. I used to think the earth was that young, but then I got interested in learning about this issue and discovered a shocking fact: those professionals who do the work, carry out the experiments, and study this for a living actually know what they are talking about.
The continents were all connected at one point (they all fit together!). The continents move at a rate of just a few inches per year. Africa and South America are over 1500 miles apart. So let’s simplify: let’s pretend that both Africa and South America are each moving five inches per year (much faster than they actually move, by the way) so that the divide between the two would grow by ten inches every year.
Twelve inches are in a foot, 5280 feet are in a mile, so one mile has 63,360 inches to it. 1500 miles is over 95 million inches. At a rate of ten inches of movement per year, it would take over 9.5 million years for Africa and South America to move to their present positions. And that’s with us using simple numbers that assume plate tectonics works faster than it really does (the tectonic plates have never been known to move five inches in a year, they tend to move, on average, a fraction of an inch every year).
And here’s the clincher: There are cracks in the Earth’s crust separating the continents that churn up lava. That lava hits the ocean floor and turns to rock, and so as the tectonic plates shift, where the lava flows gradually shifts. When we date these rocks radiometrically, the rock near the cracks (the youngest rock, because it is the most recent to be churned up) has a young age compared to the rock further away that was churned up many millions of years ago. So it all fits together. It’s hard to visualize this stuff about tectonic plates, but luckily there is a book with an easy-to-understand illustration of what I am talking about, you can find it in “The Greatest Show On Earth” by Richard Dawkins.
And Radiometric dating is a perfectly valid way to date things. There are lots of reasons to believe it is accurate, but I’ll just stick to one: we’ve tested it against historical artifacts of a known age and it gave us the right date. Pliny the younger talked about a volcano eruption that occurred over 1900 years ago, and when scientists dated the lava from this volcano it was… surprise, surprise, about 1900 years old. The folks who don’t believe radiometric dating have their own things to say on this, but those really boil down to a bunch of urban myths, and I’ll leave a link for more info at the end of this note.
References
Pliny the Younger and the Volcano Eruption Radiometrically Dated
http://www.sciencemag.org/content/277/5330/1279.abstract
Radiometric Dating Myths DESTROYED!!!
