Water vapor (H2O)
Carbon dioxide (CO2)
It is supported by the discovery that RNA can act as a catalyst.
It is supported by the fact that some viruses have RNA as their genetic material.
It suggests that there was an "RNA world" about 4 billion years ago.
It says that first RNA, then DNA, then proteins would have been necessary to interact in the chemical evolution that would have led to the development of the first cells.
Here's an interesting quiz for you.