Science Quiz

What percent of a radioactive element remains undecayed in a sample of rock after one half-life? Two half-lives? Three? Four?

After one half life, 50% of the radioactive element remains undecayed. After two half-lives, 25% remains undecayed. After three half-lives, 12.5% remains undecayed. After four half-lives, 6.25% remains undecayed.

Radioactivity

An element has the property of radioactivity when it emits rays

3. Radioactive

An element that can undergo radioactive decay is radioactive.

Radioactive dating.

Finding the age of an object by measuring the amount of a radioactive element remaining in .

Rate of decay

How quickly radioactive atoms break down into atoms of another element.

Why are layers of extrusive igneous rock near a fossil a better indication of its age?

Igneous rock extrusions are formed when lava erupts onto the surface of the earth and quickly cools into rock that is all the same age.

How does the composition of igneous rock change over time? How do scientists use this to determine the absolute age of the rock?

Over time, the amount of a radioactive element in igneous rock decreases at a steady rate. At the same time, the stable element that is formed increases at a steady rate. By measuring the amount of radioactive element remaining in the rock, scientists can determine its absolute age.

Why is potassium-argon dating used to measure the age of the most ancient rocks? Why is carbon-14 dating used to measure the age of the remains of living things?

Potassium-40 has a very long half-life (1.3 billion years) which makes it useful for dating the most ancient rock. Carbon-14 dating is used to measure the age of the remains of living things because living things are made of mostly carbon, including radioactive carbon-14.

The half-life of Potassium-40 is 1.3 billion years. What percent of potassium-40 remains undecayed in a rock that is 3.9 billion years old?

The 3.9 billion year old rock has undergone three half-lives (3.9 divided by 1.3 = 3). After 3 half-lives, 12.5% of the potassium-40 remains undecayed.

Half-life

The time it takes for half of the atoms of a radioactive element to decay.

Scientists do not use radioactive dating to determine the age of the sedimentary rock layer in which a fossil is found. Why?

Sedimentary rock is composed of sediments from rock of many different ages and is therefore not a reliable indication of the age of the fossil.

Radioactive decay

When the atoms of an element break down, releasing particles and energy.