Why is it reasonable to assume that Venus Earth and Mars sta

Why is it reasonable to assume that Venus, Earth, and Mars started with roughly the same primordial atmospheres?

Solution

Earth, Venus, and Mars all formed from the same material found in the Solar Nebula, but the origin of the atmospheres was the volcanic outgassing of H₂O, CO₂, SO₂, and N₂. Since volcanic activity was important on all three planets early in their evolution, Hence their primordial atmospheres should have been very similar.