Why did the buffalo disappear
from the Wind River prairie
ecosystem?​

Calcium and argon have the same atomic mass but have a different atomic mass because the atomic number depends upon a number of protons which is mainly different. Argon has 18 number of protons which is its atomic number and calcium has 20 number of protons. A number of neutrons and protons are different. But atomic mass (A=Z+n)  is the same. Atomic mass is the sum of the atomic number number of protons and number of neutrons.