Seacoast of Bohemia

3 Responses to “dirt age”

1. #  Jessica Smith 8:48 AM

   i think some dirt is probably 26- years old. but that's young for dirt, i would think.  

2. #  Anonymous 6:21 PM

   Your dirt-related question has given me pause, which I appreciate because I don't want to study for this test thing I have in two hours.
   
   My association with dirt has been purely along the lines of carbon trapped in dirt, mostly by means of arboreal root respiration, plant litter, or decomposition. Carbon tends to go in and out of the soil pretty quickly -- a carbon atom in the soil right now probably wasn't there ten years ago. At least, not in that same bit of dirt. But there was probably another carbon atom in its place, because the total amount of carbon doesn't change much (unless you start tilling or burning or raising cattle or spilling gasoline).
   
   So I guess it depends on how you define dirt's lifetime. If dirt is born when it has its current chemical make-up, then it's probably pretty old. How old? Well, I'd say whenever the current local biota moved in for good and moved the dirt into its current chemical equilibrium. Now, that's another matter -- consider the dirt in your yard. How different is it from the dirt + biota that was there before the housing development went up? What about before then -- did Mr.Jefferson's neighbor have a farm on the property? If it was pristine when the development went up, maybe it would go back to the last forest fire when the old biota died, mixed in with the soil, and a new mix of biota grew up. Or maybe nothing much has changed since different species rules Virginia during the last Ice Age.
   
   This definition, however, could not apply to dirt in chemical disequilibrium. One could argue that no dirt is in true equilibrium because of continuous diurnal, annual, decadal, epochal variations in atmospheric composition, hydrology, biota, and so on.
   
   The other option is to consider dirt's age as the time it's made of the exact same molecules as it is at this very moment. In that case, dirt is crazy young. Surface soil is always exchanging chemicals with the air and water by means of tiny living goobers in the dirt and by purely physical adsorption. Deeper soil's age would be dictated more by hydrology. At any rate, if you were to pick up a handful of dirt, it would immediately start exchanging chemicals with your hand and the air, and then there's the whole matter of photolysis which will just make things worse. That definition would make dirt very, very young. Like, seconds to microseconds young. (Note that applying this definition to a person would also make the person terribly young because we're always breathing, eating, sneezing, etc. Fortunately a person is not purely defined by chemical or atomic make-up. Unless you are one of those little sparkly creatures on ST:TNG that called Picard a Bag of Mostly Water.)
   
   My general conclusion: we need a better restrictions on what defines dirt. Until such a time, dirt technically does not exist.  

3. #  ginny 10:03 PM

   David! Your erudite explanation's obvious validity is just as obviously negated by your omission of the fact that the alien life-form on TNG actually called Picard an "UGLY bag of mostly water!" It makes all the difference, as you will see.