2
$\begingroup$

Do we have any tangible proof, e.g. by studying fossils of primitive life forms, that during their time the ocean was already salty, and at roughly similar levels to today's, or on the contrary, that water has no or very low salinity?

Did life had to adapt to dramatic changes in sea water salinity, as it has (I believe) for changes in air composition?

$\endgroup$
  • 1
    $\begingroup$ I've answered your first question. I suggest you post the second part (concerning adaptation to changing salinity) as a standalone question. $\endgroup$ – Dirigible Jul 22 at 15:05
2
$\begingroup$

Current estimates suggest that last universal common ancestor of life on earth lived in hydrothermal vents 3.8–3.5 billion years ago.1 Petrologic examination of quartz formed near these vents during that time suggests that seawater had a higher salinity compared to current oceans 2 --

Our data are in agreement with six other data sets—from the 3.75 Ga Isua Greenstone Belt (W. Greenland), the 3.24 Ga Pilbara region (W. Australia), the ∼3.2 Ga Barberton Greenstone Belt (South Africa; 2), the ∼2.7 Ga Matagami area (Abitibi Greenstone Belt, Canada), and the Proterozoic (∼2.2 Ga) Ongeluk Formation (South Africa). The consistency of fluid inclusion data suggests that Archean and early Proterozoic seawater may have been more saline, and potentially stratified, compared to modern seawater.

Note: Ga (for gigaannum) – a unit of time equal to 109 years.


  1. Weiss, M., Sousa, F., Mrnjavac, N. et al. The physiology and habitat of the last universal common ancestor. Nat Microbiol 1, 16116 (2016).
  2. Weiershäuser, L., Spooner, E.T.C. Seafloor hydrothermal fluids, Ben Nevis area, Abitibi Greenstone Belt: Implications for Archean (∼2.7Ga) seawater properties. Precambrian Research, Volume 138, Issues 1–2, 2005, Pages 89-123.
| improve this answer | |
$\endgroup$
  • 1
    $\begingroup$ It's amazing that the ocean was actually more salty than today -- my intuition couldn't have been more wrong. $\endgroup$ – user209974 Jul 22 at 15:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.