Question

Are there any (other than DNA) coding schemes that could happen in the hydrosphere on The Earth just after its creation ?

There is extensive literature on the idea of an "RNA World". This is the notion that early life made use of RNA rather than DNA for information storage, but RNA also had the functionality of a protein. Hence, hypothetical "RNA organisms" might have been capable of both information storage (genetics) and metabolism (done by proteins today). However, RNA and DNA are so similar chemically that this doesn't really address the spirit of the question. Some attention has been given to the idea that defects in crystal structures could have formed a rudimentary, pre-DNA coding system. This was proposed by a creative scientist names A. G. Cairns-Smith. While it is an interesting idea, it's untested (and perhaps untestable), and it requires much speculation to see how such a coding system "transitioned" to the only system of which we know - where DNA is used for information storage, and proteins are used for metabolism (with RNA serving to link these two molecular realms). Some reading on these topics, accessible to the motivated non-scientist: Seven Clues to the Origin of Life : A Scientific Detective Story by Alexander Graham Cairns-Smith. This book lays out Cairns-Smith's thesis. And, Origins of Life by Freeman J. Dyson. This one outlines various theories of life's origin, with an emphasis on Dyson's idea that metabolism may have preceded information storage.
May 1, 2002