How to solve a radiometric dating problem
A less sophisticated word for midden is “pile of garbage and often poo”.Generally speaking, archaeologists make the assumption that if the grains in and around of a clay pot are, say, 8,000 years old, then the pot itself is roughly the same age. If you had an ancient amphora sitting around, would you use it for fresh strawberry preserves? A life spent potentially confusing future archaeologists is a life well spent.At that time there would have been zero lead in it. So it was, after years of attempting to measure the age of the Earth (or, more specifically, the time since it was last molten) in a regular lab, that Clair Patterson bravely announced “Dudes and dudettes of science… ” Turns out that burning gasoline, among its other little known deleterious effects, throws lead into the air.
uranium, you’re measuring how long it’s been since that zircon formed. Radiometric dating generally involves tallying up trace amounts of material, so it’s not the sort of thing you do out in the field; you need a clean lab.
Since uranium-238 (the isotope comprising more than 99% of natural uranium) has a half-life of billions of years, it’s useful for figuring out the age of (among other things) zircons that crystallized billions of years ago. And, not for nothing, it’s also caused a thousandfold increase in lead contamination in the bodies (or bones at least) of everything that breathes and/or eats.
If you’ve ever wondered why gasoline should be “unleaded”: that’s why.
Not being made of carbon, we can’t carbon date them.
Fortunately, the stuff ancient civilization leave lying around tend to be found in clumps called “middens”.