The 18o: 16o abundance ratio in some meteorites is greater than that used to calculate the average atomic mass of oxygen on earth. is the average mass of an oxygen atom in these meteorites greater than, less than, or equal to that of a terrestrial oxygen atom?

The terrestrial oxygen atom is the atom that has an atomic mass of 16. The atomic mass of the element is calculated through the equation,

               (x₁)(M₁) + (x₂)(M₂)

where x₁ and x₂ are the percentage abundance of each of the isotope of the element. M₁ and M₂ are the atomic masses. 

In this item, it is given that the value of x₁, say corresponding to percentage abundance of 18O. With this increase, the value of x₂ will decrease then, the value of the atomic mass of the element is GREATER than that of the terrestrial oxygen atom.