Which compound was abundant in Precambrian Earth's oceans, before complex life evolved on Earth?

dissolved oxygen

dissolved carbon dioxide

dissolved methane

dissolved ammonia

The Precambrian time refers to the time 4.5 billion to 542 millions year ago. This period is characterized by having reduced atmosphere and included reduced compounds. Scientists believed that atmosphere at that time was devoid of free oxygen and CO2 was present in excess. Before the complex life evolved on the Earth, the Precambrian Earth's ocean contained dissolved carbon dioxide.