three isotopes of oxygen are oxygen-16, oxygen-17, and oxygen-18. write the symbol for each, including the atomic number and mass number.

Layer r contains a well-known index fossil that is 100 million years old. based on this information and the principle of superposition, a. layers t and m are older than 100 million years, and layers x and g are younger than 100 million years. b. layers t, m, x, and g are all older than 100 million years. c. layers t and m are younger than 100 million years, and layers x and g are older than 100 million years.