Explain how radioactive dating works, and why it works only with ...

[krzymel]

Explain how radioactive dating works, and why it works only with igneous rocks.
 
  What will be an ideal response?

Question 2

Why are supermassive galaxies often found at the cores of rich galaxy clusters?
 
  A) Most of the matter forming the cluster fell into the center to form one large galaxy.
  B) They are the result of many galactic mergers; one galaxy growing at the expense of others.
  C) Such a large galaxy attracted smaller galaxies around it to form a cluster.
  D) Large galaxies, passing a cluster, get captured into the center.
  E) Many globular clusters swarmed together to form it.

[gasdhashg]

Answer to Question 1

Radioactive dating compares the amount of a radio isotope left in a rock with its decay product; the older the rock, the less original radioactive material remains, and the more decay product has built up. Since this rate of decay is steady and predictable, that will let us get the age of an igneous rock. The igneous rocks have not been changed since they crystallized; metamorphic ones have often been heated enough to recrystalize minerals and reset the atomic clock, while sedimentary rocks are mixtures of many specimens of differing ages.

Answer to Question 2

B

[krzymel]

Both answers were spot on, thank you once again

[gasdhashg]

Great! Please up vote