## How long will it take for a quarter of the uranium 238 atoms in a rock to decay to lead 206?

about 4.5 billion years

Radiometric Dating Some examples: the half-life for the decay of potassium 40 atoms into argon 40 atoms is about 1.3 billion years, the half-life for the decay of uranium 238 into lead 206 is about 4.5 billion years, and the half-life for the decay of carbon 14 into Nitrogen 14 is 5730 years.

**What is the approximate age of an igneous rock that contains only one fourth of its original Potassium 40 content due to radioactive decay?**

The rock’s age is approximately 2.6 billion years.

**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.

### Why is uranium 238 used to measure the age of rocks?

The more lead the rock contains, the older it is. The long half-life of uranium-238 makes it possible to date only the oldest rocks. Also, the half-life of potassium-40 is only 1.3 billion years, so it can be used to date rocks as young as 50,000 years old.

**How long is the half-life of uranium-238?**

The half-life of uranium-238 is about 4.5 billion years, uranium-235 about 700 million years, and uranium-234 about 25 thousand years.

**How old is a rock which contains uranium-238 and has undergone 2 half-lives?**

The half – life of U 238 is about 4.5 billion years. As time passes, the ratio of Pb 206 to U 238 will increase and it is this which enables the age of the rock to be estimated.

#### What is the half-life of uranium 235?

about 700 million years

**Is the half-life the same length of time for carbon-14 and uranium 238 transitions?**

Explanation: Carbon 14 with a half life of 5,700 years can only be used to date fossils of approximately 50,000 years. Most fossils are thought to be much older than 50,000 years. Uranium 238 has a half life of 4.5 billion years.

**What is the half-life of uranium-238?**

## How old is a rock which contains uranium-238 and has undergone 2 half lives?

**Why does uranium-238 have such a long half-life?**

Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. Due to its natural abundance and half-life relative to other radioactive elements, 238U produces ~40% of the radioactive heat produced within the Earth.

**What is the half life of uranium 238 and 235?**

The half-life of uranium 238 is of 4.5 billion years, while uranium 235 has a half-life of ‘only’ 700 million years. Though both isotopes were at the time of Earth formation equally abundant, natural uranium today consists today of 99.3% uranium 238 and only 0.70% uranium 235. Rest of the detail can be read here.

### How much uranium is in the a rock?

A rock is found contains uranium-238 and also lead-206. Scientist analyze the rock for these two elements and find that the total mass of uranium in the rock is 2.40 g, while the amount of lead is 1.11 g.

**What is the mass of uranium-238 and lead-206?**

A rock is found contains uranium-238 and also lead-206. Scientist analyze the rock for these two elements and find that the total mass of uranium in the rock is 2.40 g, while the amount of lead is 1.11 g. How old is this rock? Uranium-238 ( λ = 4.5×109 yr) decays through several steps until it finally decays into lead-206.

**What is the half-life of Pb 206 and U 238?**

The half – life of U 238 is about 4.5 billion years. As time passes, the ratio of Pb 206 to U 238 will increase and it is this which enables the age of the rock to be estimated. We need to do some “math” to show this:

https://www.youtube.com/watch?v=ZRmABgecY00