The oceans, which cover more than 71% of the earth's surface, are enigmatic and vital ecosystems that play a pivotal role in the planet sustainability. Oceans are believed to have formed from volcanic outgassing and the accumulation of water vapor during the cooling phase of the planet. Ocean water contains essential elements that sustain rich biodiversity and contribute significantly to the global water cycle. The interconnected nature of the oceans influence weather patterns, nutrient cycling and distribution of heat around the planet. Ocean productivity plays a major role in regulating the climate by influencing carbon sequestration and their burial. As anthropogenic activities introduce a large spectrum of pollutants and radioactive substances into the ocean, comprehensive monitoring is essential for developing effective management strategies to minimize the impacts. A comprehensive introduction to the oceans, biogeochemistry and the challenges in the Anthropocene epoch are presented here.