Radioactive Decay & Half Lives

Explain that populations of organisms (“species”) have changed across time and identify the evidence scientists use evidence to support this theory.

Analyze data and use data as evidence to support an idea.

Summarize the evidence for change across time from the perspective of many fields of science.

So one fossil sees another fossil off in the layer above him. He says, “So, how long have you been dating?”

The other fossil didn’t respond.

“Yeah, forget about it!” he responded, “I’m half the Dinofish I used to be!”

Read the following essays and answer the questions in your journal:

Fossils: Traces of Life Gone By List three ways fossils can be formed. What parts of the organisms are typically fossilized? Observe the diagrams on p.103(figure E2-1) – and write down

one observation.

Technologies That Strengthen Fossil Evidence Generally describe how radioactive carbon dating tells us the

age of fossils. Explain why this method is important for studying fossils

Radioactive Isotope: Elements that undergo steady decay and can be useful for determining the age of objects. Examples: C-14

Half-Life: the rate at which radioactive isotopes decay (which varies for each element/ substance.)

One half-life is the amount of time it takes for half of the atoms to change into something else.

Scientists can apply the concept of half life and calculate approximate age by looking at how much “stuff” is left in the fossil.

If the half-life of an element is 30 days,

How much time would it take to reduce the amount of the element to 2.5 grams, if you started with 10grams of the element??

It takes 2 half lives or 60 days for the element to reduce to 2.5 grams.

Ready to try one on your own?

If an Element’s half life was 10 days, and you began with 75 grams of an element, how many half lives would it take to reduce the element to less than 5 grams?

How much time would it take?

Hint: Draw a table!

4 half lives or 40 days