07.3 Dating Planetary Surfaces

What is one way that astronomers have actually gotten an idea of the age of the surfaces of terrestrial planets other than the Earth?

• looking at the colors different surfaces show

• bringing back samples and run radioactive dating tests

• counting craters

• measuring the thickness of the atmosphere above each surface

• looking in the instruction manual that comes with each planet

In studying the surfaces of solid bodies in the solar system, astronomers have learned that the number of craters (per unit area):

• is about the same on every world

• is greater as you get closer to the Sun

• is greater as you get further and further from the Sun

• is roughly proportional to the age of the surface we are examining

• follows no discernible rules or relationships at all

The rate at which a collection of the same radioactive atoms will decay depends on:

• the amount of radio waves falling on the material

• the amount of light falling on the material

• the temperature of the material

• the size of the planet or moon on which the material is located

• only on internal processes within the atoms; nothing external matters

In a bad late-night science fiction film, a villain is using a large collection of rare radioactive atoms as energy for a weapon to threaten the good guys. The atoms have a half-life of 1 hour. The villain has 4 kilograms of the radioactive material now, and he needs a minimum of 1 kg. for his weapon to work. After how much time will the weapon no longer be a threat?

• just a little after 1 hr

• just a little after 2 hrs

• just a little after 4 hours

• just a little after 16 hours

• can't be determined from the information given

In radioactive dating, the measure scientists use to note how long (on average) a particular radioactive nucleus will take to decay is called its

• radioactive ratio

• parent-daughter criterion

• half-life

• geological activity

• Tinder activity

On Earth, we can get the age of various parts of our planet by finding rocks that contain radioactive atoms. Which other world do have a good number of rocks from to do this kind of age analysis?

• Venus

• The Moon

• Halley’s Comet

• Jupiter

• You can’t fool me, there is no other world from which we have rocks

Radioactive dating techniques have revealed that our Earth and Moon are approximately how old?

• about 6,000 years

• about 2 million years

• about 100 million years

• about 4.5 billion years

• you can't fool me, we have no way of measuring ages as old as the Earth's

Put the following % of the radioactive isotope (parent) in order from 0 half-lives to 4 half-lives:

• 12.5% parent

• 50% parent

• 6.25% parent

• 100% parent

• 25% parent

Answer explanation

0 half-lives --> 100% parent

1 half-life --> 50% parent

2 half-lives --> 25% parent

3 half-lives --> 12.5 % parent

4 half-lives --> 6.25 % parent

Put the following % of the stable daughter in order from 0 half-lives to 4 half-lives:

• 93.75% daughter

• 75% daughter

• 0% daughter

• 87.5% daughter

• 50% daughter

Answer explanation

0 half-lives --> 0% daughter

1 half-life --> 50% daughter

2 half-lives --> 75% daughter

3 half-lives --> 87.5 % daughter

4 half-lives --> 93.75 % daughter

Which radioactive isotope should be utilized to date a rock from the Archean Eon?

• Carbon-14

• Nitrogen-14

• Calcium-40

• Uranium-238

Answer explanation

Uranium-238 has a long half-life so it will be utilized to date very old things.