How salty has the sea been over the past 541 million years?

Take a bottle of water from the sea and try to drink it. You gag and your lips pucker. After all, dissolved in that liter of the ocean are around 35 grams of salts (mostly sodium chloride). Now, imagine you tried to do this same thing 1 million years ago, 10 million years ago, 100 million years ago, even 500 million years ago (that is, throughout the Phanerozoic eon). Would you ever be able to drink the water? Alternatively, would the sea ever have been so salty that today’s ocean creatures would not have survived? A 2006 article by Hay et al. helps answer precisely these questions. The authors tracked variable chloride levels to demonstrate how salinity has changed throughout the Phanerozoic, noting a significant overall decline. These changes have had important effects on ocean circulation and on plankton levels — and possibly contributed to the explosion of complex life in the Cambrian, 541–520 million years ago. Continue reading