Origin of life. A simpler nucleic acid.

What was the genetic material of the earliest life forms on Earth if it was not RNA? As Orgel explains in his Perspective, the answer may be simpler nucleic acid polymers perhaps like the RNA analogs called (L)-a-threofuranosyl oligonucleotides or TNAs (Schöning et al.). These molecules have threose rather than ribose in their sugar-phosphate backbones and yet retain many of the properties of RNA including the ability to pair up in double helices.