DATING PAST ERUPTIONS

Taupo Times, Volume IV, Issue 174, 27 May 1955, Page 7

DATING PAST ERUPTIONS

Modern Research Method It is only in the last year or so that any degree of certainty has been reached by scientists as to when, in terms of years, the vast eruptions took place which covered so many square miles of the central North Island with pumice. And when it was recentlyxdisclosed that modern methods of research had established that the most recent of these devastating outbursts occurred some 1700 years ago, considerable interest was roused as to what these methods were. The method used for "dating" prehistoric remains is one which records the radiations from carbon-14 (the radio-active isotope of carbon). The Taupo eruptions have been "dated" by applying this method of inquiry, which originated in America, to specimens of the carbonised wood associated with the volcanic deposits. All living matter maintains a constant balance of the rare radio-active isotope carbon-14 and the ordinary isotope carbon-12, but when theanimal or plant dies it gradually loses the carbon-14 at a defined rate 'by radio - active decay. By measuring the amount of this activity left in fossilised remains scientists can tell to within certain limits the years the animal, plant, etc., existed as living matter. Previous Limitation Until rec^ntly chemically-prepared pure solid carbon was placed in the specially-designed Geiger-Muller apparatus for measuring radio-activity. The chemical procedure was long and tedlous, the success of the preparation depended largely on the radio-chemical purity of the chemicals used (particularly the magnesium metal), and the dating was limited to 25,000 years ago. From the commencement of the development of this work in New Zealand, research workers sought better processes, especially as at times the work had to stop because magnesium metal free from radio-chemical impurities could not be obtained. The task - set was to develop a simpler method that would be more accurate, less time-consuming in sample preparation, and to be able to date back further than was possible with the solid carbon method. Looking Fiirther Back ' After considerable study and re-

search a process has been developed that more than meets the task set the physicists and chemists, and thorough tests and checks have just been completed. In- one day, the new detecting equipment will give ages up to 42,000 years, and to 15,000 years in two days. The new method greatly simplifies the chemical operations, and it would be difficult to plan a simpler chemical procedure to yield a gas havlng good counting characteristics. It is now possible to commence the combustion of a carbonaceous specimen, purifying the carbon dioxide, and fill the counter in a working day. The sample can be checked for contamination by a few minutes counting and after an overnight - count of 1000 minutes the age of the specimen is determined.