Final answer:
The most likely first self-replicating molecules were RNA molecules, according to the RNA World Hypothesis, which suggests early life was based on RNA's ability to encode genetic instructions and catalyze chemical reactions. Option D.
Step-by-step explanation:
The question posed here centers around the hypothesis of the first self-replicating molecules on Earth. Scientific research and theories have led to the RNA World Hypothesis, which proposes that early life was solely based on RNA because it had the capability to both store genetic information and catalyze chemical reactions.
This hypothesis resolves the 'chicken-and-egg' problem of which organic molecule, required for the continuation of life, came first since RNA can perform the crucial functions of both DNA and proteins.
Considering the evidence provided and the current scientific consensus, the most likely answer to the posed question is D. RNA molecules. The hypothetical first cell likely contained RNA within a phospholipid bilayer, making RNA a fundamental part of the earliest forms of life.
Although other alternatives like Amino-Adenosine Triacid-Ester (AATE) are known to be self-replicating autocatalysts today, RNA is more widely accepted as the original self-replicator due to its dual functionalities and its role in contemporary cellular machinery. So Option D.