Question

the graph shows calculations for potassium - argon dating.
which statement explains what geologists can learn from the graph?
they can estimate that all the potassium will have decayed within 6.5 billion years.
they can tell that 1/8 of the argon gas will be left after 3.9 billion years.
they can determine that a rock is 1.3 billion years old if 1/2 of the potassium has decayed.
they can see that potassiums half - life varies from every 1.3 billion years to every 5.2 billion years.

Explanation:

Step1: Analyze the graph

The graph shows the relationship between the remaining portion of potassium and time (in billions of years).

Step2: Check the key data point

When looking at the graph, for a rock with a certain proportion of potassium - argon, if we consider the point where the characteristics match (for example, when the proportion of potassium remaining corresponds to the time scale on the y - axis). In this case, when we look at the data points and the time - potassium relationship, we can see that when we want to determine the age of a rock, we can use the graph to find the corresponding time. For instance, if the conditions (based on the potassium - argon ratio) match the 1.3 - billion - year mark on the graph (by looking at how the potassium has decayed over time as shown in the graph), we can conclude the rock's age.
So, geologists can use the graph to determine that a rock is 1.3 billion years old.

Answer:

They can determine that a rock is 1.3 billion years old.