1. which characteristic of potassium makes it useful for dating rocks?

it has a long half-life.
it decays at an unknown rate.
it produces lead as it breaks down.
it can be used to date all types of rock.

2. which statement describes the law of superposition?

sedimentary rocks were originally in horizontal layers.
in horizontal rock layers, each layer is younger than the one below it.
rock layers must be in existence before something can happen to them.
rocks that are not in horizontal layers were shifted by some geologic event.

1.) the first option. Its half life is 10 to the 9th power YEARS!

2.)The last option. There must have been diversion or something if it is not horizontal.!

Hope this helped!!!^_^

1- option (A)

2- option (B)

Explanation:

Potassium is widely used in the Potassium-Argon dating method. It is efficient in determining the age of rocks, that is up to about 4 billion years old. Potassium-40 is highly unstable and found to be present in many rocks. It has a very long half-life which is about 1.3 billion years and gives an accurate age of the rocks.

According to the law of Superposition, in a set of horizontal layers of rocks, the rock layers that are at the bottom are the oldest rocks and the rocks that are present at the top are the youngest rocks.

Thus, the correct answers to the given questions are given above.

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.