Some zircons are obviously disturbed and can be ignored, while other cases are harder to judge.In these cases, the concordia diagram is a valuable tool.
Uranium easily substitutes for zirconium while lead is strongly excluded.
This means the clock is truly set at zero when zircon forms.
Lead atoms created by uranium decay are trapped in the crystal and build up in concentration with time.
If nothing disturbs the grain to release any of this radiogenic lead, dating it is straightforward in concept.
Though the teen birth rate has declined to its lowest levels since data collection began, the United States still has the highest teen birth rate in the industrialized world.