Tutor profile: Alison W.

How do we use rocks to date things and determine how old they are?

Through a method called decay rate, or radioactive dating. Rocks and sediments contain unstable atoms called isotopes that decay over time. Different isotopes decay at different rates. If we know the time it takes for an isotope to decay, and we find that isotope within a rock or sediment we can use that information to determine how long the rock has been there and how old it is. A common isotope used to date rocks is Carbon.

What does the Law of the Conservation of Mass have to do with a chemical equation needing to be balanced?

The Law of Conservation of Mass states that matter can neither be created nor destroyed. In a balanced chemical equation, you need to have the same number of each atom on both the reactant and the product side, this is because we need to account for all of the matter. We should have the same amount going in as we do going out because matter is only transferred, not made or destroyed.

Two parents with brown eyes have two children. One of the children has brown eyes as well, but the other has blue eyes. How is it possible for the blue eyed child to be the real child of these parents?

The parents must be heterogenous for the eye color trait, meaning that both of their genotypes are Bb. The capital B represents the dominant trait, brown eyes and the lowercase b represents the recessive trait, blue eyes. If we set up a Punnett square, we'd see that their children have a 25% chance of having the combination BB for brown eyes, a 50% chance of having the combination Bb for brown eyes, and a 25% chance of having the combination bb for blue eyes. Therefore it is possible for that to be their child.