# The ratio of strontium isotopes in seawater, which should change due to long-term erosion, has varied by only 0.35% throughout history. In fact, its value today is exactly the same as in the oldest samples, which are claimed to be from 500 million years ago. | # The ratio of strontium isotopes in seawater, which should change due to long-term erosion, has varied by only 0.35% throughout history. In fact, its value today is exactly the same as in the oldest samples, which are claimed to be from 500 million years ago. |