mesure des temps

OBS: géologiques par la radioactivité (René Coppens) Méthode des halos pléochroïques (pleochroic halos) de (à) l'hélium (helium) du (au) plomb total, commun (techniques modernes, p. 17) (lead) des plombs isotopiques; du strontium (du rubidium et du strontium) (rubidium-strontium) au strontium (techniques modernes, p. 17) du plomb-alpha (lead-alpha: Larsen's)

CONT: ... it would be wrong to think of these common-lead and common-strontium methods as competing with the conventional dating techniques, since the radioactive decay processes occurred in systems which are unknown or which are not available for study. This is a substantial handicap in evaluating an age determination, but does not illuminate the ultimate origin of the lead and strontium now found in common rocks and minerals.