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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.
Other minerals sometimes used for uranium-lead dating include monazite, titanite and two other zirconium minerals, baddeleyite and zirconolite.
However, zircon is so overwhelming a favorite that geologists often just refer to "zircon dating." But even the best geologic methods are imperfect.
As a woman, I know that sometimes talking about gender with a male partner – even if he’s well versed in all things feminist – can feel exhausting.
Sometimes I don’t want to chat with someone who only has a theoretical understanding of gender oppression.
Uranium comes in two common isotopes with atomic weights of 235 and 238 (we'll call them 235U and 238U).
Both are unstable and radioactive, shedding nuclear particles in a cascade that doesn't stop until they become lead (Pb).
Consider the concordia: as zircons age, they move outward along the curve.The 235U–207Pb cascade has a half-life of 704 million years and the 238U–206Pb cascade is considerably slower, with a half-life of 4.47 billion years.So when a mineral grain forms (specifically, when it first cools below its trapping temperature), it effectively sets the uranium-lead "clock" to zero.With this background in the uranium-lead method, you may have a deeper appreciation of the research presented on the University of Wisconsin's "Earliest Piece of the Earth" page, including the 2001 paper in Nature that announced the record-setting date.
That is, unless you count my first boyfriend – José – who, in the second grade, long-distance collect-called me from Puerto Rico and got me in a lot of trouble with my dad. But I think it’s worth revisiting these concepts within the context of romantic or sexual relationships. And the way we practice our allyship in those contexts should reflect that.
But now imagine that some geologic event disturbs things to make the lead escape.