Did the first cells evolve in soda lakes?
According to a new study by Zachary R Cohen of the Chemistry Department of Washington University, Seatle, WA, USA and colleagues, soda lakes which are rich in sodium and carbonates could have provided the right conditions for the simplest, RNA-based cells to have arisen.
It is widely assumed that the earliest simple cells were based on RNA enclosed in a lipid membrane but there is a problem in that RNA requires divalent ions such as Magnesium (Mg2+ to function, but Mg2+ damages lipid membranes, so it isn't easy to explain how they could have co-existed within the same cell structure.
So the question is whether the low levels of (Mg2+ found in soda lakes, such as the Last Chance Lake in British Columbia, Canada, could have provided the right conditions of enough (Mg2+ for RNA to function but not so much as to prevent the formation of an enclosing membrane.
To explore this possibility, Zachary Cohen and his colleagues collected water from Last Chance Lake and the similar but subtly different Goodenough Lake after seasonal evaporation. According to information from Washington University published in phys.org:
These soda lakes each contained ~1 M Na+ and ~1 mM Mg2+ at pH 10. The authors found that spontaneous extension of short RNA primers occurred in lake water at a rate comparable to the rates in standard laboratory conditions.The scientists give more technical details in their open access paper in PNAS Nexus:
The authors added fatty acids, which could have been available on the early Earth, to the lake water to see if the molecules would assemble into membranes. The membranes formed in dilute water that simulates a rainfall event, and the membranes persisted even when surrounded by concentrated lake water from the dry season.
According to the authors, soda lakes on the early Earth could have supported key features of protocell development, with RNA copying and ribozyme activity taking place in the dry season and vesicle formation occurring during the wet season.