select the correct answer.\nwhich compound was abundant in precambrian earths oceans, before complex life…

Brief Explanations:

Before complex life evolved, the atmosphere and oceans had different compositions. Photosynthetic organisms like cyanobacteria later changed the oxygen levels. In the Precambrian, before extensive oxygen - producing life, dissolved carbon dioxide was more abundant. Dissolved oxygen (A) became more prominent after photosynthetic life (like cyanobacteria in the Great Oxidation Event). Dissolved methane (C) and ammonia (D) were not as abundant as carbon dioxide in the context of oceanic composition before complex life evolution related to the key role of carbon - based early chemical and biological processes (even before oxygen - rich environments).

Answer:

B. dissolved carbon dioxide