26 October 2006

Blind dates?

Scientists looking at some of the first rocks to be dated have decided that rocks which had taken “10 million years” to form — instead found under study that “most of the formations originated during the Ireviken event, which lasted for only 1 million years or so.”

Really, that replaces about 10 megayears with “only 1 million years or so”, and since many, many other rocks are dated based on these ages, it looks like much other rock is about to lose 9 million or so years.

What surprises me is that they’re basing these dates on “the ratio between two isotopes of carbon, carbon-13 and carbon-12, in a rock sample,” but carbon isotopes decay fairly fast — maybe 100 kiloyears tops — so I wonder about this being used on rock which is aged at hundreds of millions of years old. Well, perhaps that’s another thing that will be re-considered while they’re analysing everything.

It’s going to be interestig to see what various implications arise (what ideas change) as rocks with formally “certain” dates gradually get new birthdays. Will formations change as a unit, or will parts “move” relative to the rest? What events are going to swap places? What pet theories will have to find new homes?

4 comments:

Major said...

some carbon isotopes decay fast.

C-12 and C-13 are both regarded as "stable" (not radioactive); their half-life in the billions of years.

Major said...

This "9 million year difference" needs to be put into context. The calculated age of the bottom if the formation has not changed. The age of the top of the formation has been re-calulated at 418 million years rather than 426 million years; a correction of roughly 2%.

All of which stikes me as a much more serious problem for psuedo scientists who want to prove that the earth is 10k years old than for real goeologists.

Leon Brooks said...

C-12/C-13: yup, sorry, ’tis C-14 which vanishes so fast, so a C-14 date for any of this would be nonsense but the stabler isotopes make a better argument.

2% difference: the correction is across the absolute rate of formation, not across the rocks’ entire lifespan. That’s why there is a fuss in the first place — much other rock dated using the same process is going to need editing. One of the risks of basing everything on one’s optimistic first guess, probably.

The dudes wanting 10ka — AFAICT — are down on the whole set of assumptions underlying this method of dating, rather than the “mere” 5- to 10-fold change in elapsed time which is distressing more-conventional geologists.

Major said...

Do you have some reason to believe that they measured the rate of formation directly as opposed to measuring the start and end times. The press release you linked is vague on this and the work does not appear to have made it into the formal literature yet.

If they measured the rate directly then this is indeed a big change but if they just measured start and end times then I stick by my conclusion that this only constitutes a 2% error on one end (both start and end times presumably being measured as years BP).