Final answer:
Oxygen was discovered in the 1770s by chemists including Joseph Priestley and Carl Wilhelm Scheele, even though it was present in the atmosphere much earlier. Antoine Lavoisier named it and discovered its role in combustion and the formation of the Earth's ozone layer.
Step-by-step explanation:
Oxygen was indeed discovered much later than it existed in Earth's atmosphere. It can be surprising to consider that elemental oxygen, a substance vital to the survival of many forms of life, wasn't recognized until the 18th century. Despite the presence of oxygen in the atmosphere for billions of years, its discovery is attributed to multiple chemists in the 1770s, including Joseph Priestley and Carl Wilhelm Scheele. The formal recognition and naming of oxygen as a chemical element were done by Antoine Lavoisier, who coined the name and also identified its pivotal role in the process of combustion.
Oxygen's presence in the Earth's atmosphere began accumulating approximately 2.4 billion years ago, transforming the planet's environment and making it possible for life to thrive on land as well as in the sea. The interaction of sunlight and atmospheric oxygen also led to the creation of the ozone layer, which protects from harmful ultraviolet radiation.