Was it true that ancient earth did not contain much oxygen?

The assertion that ancient Earth did not contain much oxygen is indeed true. During the early stages of Earth's history, particularly in its formative years, the atmosphere was primarily composed of gases like methane, ammonia, and hydrogen, with very little free oxygen present. It wasn't until photosynthetic organisms, particularly cyanobacteria, began to thrive around 2.4 billion years ago that significant amounts of oxygen started to accumulate in the atmosphere through the process of photosynthesis. This marked the beginning of the Great Oxidation Event, which dramatically changed the composition of the atmosphere and allowed for the evolution of aerobic organisms.

Understanding this context is crucial, as it highlights the transformative role of early life forms in shaping the Earth's environment. Prior to the proliferation of oxygen-producing organisms, the conditions on Earth were vastly different and not conducive to the complex life forms that we see today.