A new study suggests it might have been:
In simulated ancient seawater, clay forms a hydrogel — a mass of microscopic spaces capable of soaking up liquids like a sponge. Over billions of years, chemicals confined in those spaces could have carried out the complex reactions that formed proteins, DNA and eventually all the machinery that makes a living cell work. Clay hydrogels could have confined and protected those chemical processes until the membrane that surrounds living cells developed.
Scientists previously suggested that tiny balloons of fat or polymers might have served as precursors of cell membranes. Clay is a promising possibility because biomolecules tend to attach to its surface, and theorists have shown that cytoplasm—the interior environment of a cell—behaves much like a hydrogel. And, Luo said, a clay hydrogel better protects its contents from damaging enzymes (called “nucleases”) that might dismantle DNA and other biomolecules.
(Colour emphasis added to signify certainty.)
Clay isn’t a new origin of life idea. It has been championed by origin of life (OOL) researcher A. G. Cairns-Smith, as a rival to “RNA world” (RNA, they claim, happened to evolve before DNA), which he labelled “absurd to imagine” because there are “14 major chemical/molecular hurdles”against more primitive nucleotides like RNA. Remember this; you won’t hear it from tax-funded textbooks introducing RNA world.
Information theorist Hubert Yockey dismisses clay world because clay crystals offer very little information. A crystal structure repeats the same information indefinitely, whereas life’s minimum information density is somewhere around the level of DNA. And OOL theorist Leslie Orgel (1927–2007), who championed RNA world, noted that if clay had the structural irregularities needed to enable RNA to emerge, it probably wouldn’t reproduce it accurately. 
But these guys wrote this stuff a while back, so it is doubtless time to throw some clay again. The hydrogel thing sounds new; let’s see what RNA world supporters (and others) say about that.
A. G. Cairns-Smith, Seven Clues to the Origin of Life: A Scientific Detective Story, , Cambridge University Press: Cambridge UK, 1993, reprint, pp.46-48.
 Hubert Yockey, “Self Organization Origin of Life Scenarios and Information Theory,” Journal of Theoretical Biology, Vol. 91, 1981, p. 14.
 Leslie Orgel (1927–2007), “Origin of Life on the Earth,” Scientific American, vol. 271, October 1994, p. 78.