Answer
b. iron-sulfide cofactors
Work Step by Step
Because iron-sulfide cofactors are found in modern organisms, researchers hypothesize that the first life emerged from rock chambers next to deep-sea hydrothermal vents. Rocks around the vents are infused with iron sulfides, and gases such as carbon dioxide and hydrogen cyanide spewing from the vents accept donated electrons coming from the iron sulfides. By accepting these electrons, the gases become reactive, forming organic compounds such as pyruvate. The new compounds build up inside small rock chambers that are the size of cells. The accumulation of these compounds gave rise to the first catalytic molecules called enzymes.
