Earth’s oceans were likely not always salty in the way they are today. Early in Earth’s history, during the Archean eon (about 4 to 2.5 billion years ago), the first oceans probably formed as freshwater from condensed water vapor released by volcanic outgassing. As this water interacted with the newly forming crust, it began dissolving minerals and salts from the rocks, gradually increasing the ocean’s salinity over hundreds of millions of years[1].
Research suggests that the early oceans may have been even saltier than today, possibly up to twice the current salinity, due to intense volcanic activity and limited continental land to remove salts[2][4][6]. Over geological time, processes such as the formation of continents, plate tectonics, and large-scale evaporite (salt deposit) formation acted as “sinks” that removed salts from seawater, balancing the inputs and stabilizing ocean salinity to around today’s average of about 35 parts per thousand (ppt) by the Miocene epoch (~23 million years ago)[1][3].
Thus, the oceans transitioned from likely fresh or low-salinity water to very salty conditions early on, and then gradually settled to a relatively stable salinity level through a dynamic balance of sources and sinks over billions of years. This long-term evolution influenced ocean chemistry, circulation, and the development of life.
Summary:
– Earth’s first oceans were likely fresh water formed from condensed volcanic water vapor.
– Over time, water dissolved salts from rocks, making oceans salty.
– Early oceans may have been saltier than today, possibly twice as salty.
– Geological processes removed salts, balancing ocean salinity to modern levels (~35 ppt) by about 23 million years ago.
– Ocean salinity has fluctuated but remained relatively stable over millions of years since then.
Sources:
[1] Geosciences LibreTexts – Salinity over Long Timescales
[2] Nature – Salinity history of the Earth’s early ocean
[3] Aliosha Bielenberg – How Salty Has The Sea Been Over the Past 541 Million Years?
[4] Yale News – Earth’s early oceans may have been heavy on the salt
[6] ScienceDirect – Temperature and salinity history of the Precambrian ocean
Read More
[1] https://geo.libretexts.org/Bookshelves/Oceanography/Our_World_Ocean:_Understanding_the_Most_Important_Ecosystem_on_Earth_Essentials_Edition_(Chamberlin_Shaw_and_Rich)/03:_New_Page/08:_The_Water_Cycle_and_Ocean_Salinity/8.05:_Salinity_over_Long_Timescales
[2] https://www.nature.com/articles/26879
[3] https://alioshabielenberg.com/how-salty-has-the-sea-been-over-the-past-541-million-years/
[4] https://news.yale.edu/2021/12/13/spice-world-earths-early-oceans-may-have-been-heavy-salt
[5] https://en.wikipedia.org/wiki/Paleosalinity
[6] https://www.sciencedirect.com/science/article/pii/S0031018204005905
[7] https://www.reddit.com/r/askscience/comments/7nu3an/has_the_salinity_of_the_earths_oceans_changed/
[8] https://www.britannica.com/science/seawater/The-early-oceans