Which of these three molecules-DNA, RNA, or proteins-most likely operated in the ancient past prior to the appearance of the other two molecules? Explain how this earliest "proto-life" chemical serves more than one function.

RNA

Explanation:

It's important to first acknowledge that in order to sustain life, there needs to exist molecules that can self-propagate. These molecules need to perform essential functions that include:

1) Storing genetic material that can be copied.

2) Be catalysts for processes such as replication and other functions.

Between the 3 molecules, RNA is the only one that has both properties. It is a polynucleotide, meaning that it stores genetic material that can be copied. It can also fold into complex tertiary structures that act as catalysts. Therefore, it is possible that it acted primitively as an autocatalyst making copies of itself, directly or indirectly.