Question: How is the ratio of uranium to lead determined?

One form of uranium–lead dating depends on measuring the ratio of the amount of helium trapped in the rock to the amount of uranium present (since the decay 238U → 206Pb releases eight alpha-particles).

What is the ratio between uranium and lead?

137.7:1 All naturally occurring uranium contains 238U and 235U (in the ratio 137.7:1). Both isotopes are the starting points for complex decay series that eventually produce stable isotopes of lead. U decays to 206Pb (half-life = 4510 Ma, see decay constant) by a process of eight alpha-decay steps and six beta-decay steps.

What does the ratio of uranium and lead in rock tell scientists?

Scientists discovered that rocks could be timepieces -- literally. By measuring the ratio of lead to uranium in a rock sample, its age can be determined. Using this technique, called radiometric dating, scientists are able to see back in time.

How is the uranium to lead ratio in a rock used to estimate its age?

Uranium-Lead Dating Two isotopes of uranium are used for radiometric dating. Uranium-238 decays to form lead-206 with a half-life of 4.47 billion years. Uranium-235 decays to form lead-207 with a half-life of 704 million years. Uranium-lead dating is usually performed on crystals of the mineral zircon (Figure 11.26).

How old would a sample with 50% uranium-238 and 50% lead-206 be?

After a second half-life, the 50 gm of U-238 would drop to 25 while the 50 gm of Pb-206 would increase to 75. Thus, two half lives. Since the half-life of U-238 is 4.5 Billion years, this rock must be 9 BY old. 1d.

How much uranium 206 is in the rock sample?

Problem #58: A sample of rock contains 64.27 mg of U-238 (isotopic mass 238.0508 amu) and 22.66 mg of Pb-206 (isotopic mass 205.9745 amu). Assuming that radioactive decay of U-238 is the only source of Pb-206, estimate the rocks age. Half life of U-238 radioactive disintegration is = 4.468 x 109 years.

How long does it take for uranium to become lead?

RADIOMETRIC TIME SCALEParent IsotopeStable Daughter ProductCurrently Accepted Half-Life ValuesUranium-238Lead-2064.5 billion yearsUranium-235Lead-207704 million yearsThorium-232Lead-20814.0 billion yearsRubidium-87Strontium-8748.8 billion years2 more rows•13 Jun 2001

How long does it take for 50% of U-238 to decay to PB-206?

about 4.5 billion years After conducting careful measurements on large numbers of U-235 atoms, scientists determined that each U-238 atom has a 50% chance of decaying into Pb-206 during about 4.5 billion years. In other words, the half-life of U-238 is 14 billion years.

What is U-238 and PB-206 used for?

The uranium radioactive series has been used to estimate the age of the oldest rocks in the Earths crust. The ratio of U-238 to Pb-206 in a rock changes slowly as the U-238 in the rock decays.

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