3 Things You Should Know About Evolution | Testbook.com

Oxygen, being the third most abundant element in the universe, is found at the core of stars. However, over 3 billion years ago, our planet was without oxygen. The life forms during that period were reliant on other prevalent elements such as methane and hydrogen. The first to harness the sun's energy were the cyanobacteria. These organisms had the ability to produce their own food and release oxygen as a by-product of their metabolism, much like today's photosynthetic plants. Gradually, oxygen infiltrated the landscape and accumulated in the atmosphere.

Life as we understand it today did not appear abruptly within a brief time frame. It is believed that life's precursors started as straightforward, nonliving chemicals that could replicate themselves. The DNA structure, which underpins all life on earth, evolved from RNA. Stanley Miller's experiments in the early 1950s partially supported this theory. He replicated the conditions of ancient earth in his experiment and managed to produce essential organic compounds required for life. However, the shift from these basic organic compounds to the complex, self-replicating structure that characterizes all life on earth today remains unexplained.

Presently, we know that there are five oceans and seven continents on the earth. But 270 million years ago, all the continents converged into a massive landmass surrounded by a vast ocean, named Pangea and Panthalassa respectively. This setting led to extreme climatic and weather conditions. There were enormous temperature variations, and super-hurricanes and storms that devastated the ancient landscape.

In summary, life on earth did not appear suddenly. It is the product of billions of years of evolution shaped by countless factors. Essentially, all life on earth is interrelated to some extent. For instance, humans and the sea anemone, though it resembles a plant, both belong to the animal kingdom.