Answer:
Due to presence of these structures in ancient as well as modern organisms.
Explanation:
Homologous and vestigial structures are the evidences that show evolutionary relationships between organisms because these structure were also present in the ancient ancestor of that organism. These homologous and vestigial structures shows the relationship between the ancient and the modern organisms. Some structure has a purpose and function in the body of ancient organisms but with the passage of time those structure are useless and have no function in the body but these structure shows connection between modern and ancient organisms.
Oxygen and silicon make up most of earths crust
as in any liquid, as heat is added, solutions become more capable of holding more dissolved material . (not sure if this is what you're asking as it seems to be missing information)
The concentration of CO2 would drastically increase.
