Within the first billion years of Earth’s history, life appeared in the oceans and began to affect the Earth’s atmosphere and surface, leading to the proliferation of anaerobic and, later, aerobic organisms. Some geological evidence indicates that life may have arisen as early as 4. 1 billion years ago. Since then, the combination of Earth’s distance from the Sun, physical properties and geological history have allowed life to evolve and thrive. In the history of life on Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that ever lived on Earth are extinct. Estimates of the number of species on Earth today vary widely; most species have not been described. Over 7. 7 billion humans live on Earth and depend on its biosphere and natural resources for their survival. Humans have developed diverse societies and cultures; politically, the world has around 200 sovereign states.
The need to comprehend and explain our origins--the world of natural phenomena--cannot be properly viewed as exclusively scientific. Instead, it should be viewed as something generally human. Through enchanting, magical narratives involving super-human heroes and heroines, as well as anthropomorphic gods and goddesses, ancient pre-scientific societies attempted to explain and make some order out of the mysterious complexities of the Cosmos. Earth's Moon has always held a place of special fascination for our species, inspiring our human imagination to escape its troubling limitations and--as we search beyond our Earthbound lives--help us to move towards an understanding of who we are, in all our human complexity. Therefore, ancient gods and goddesses mimic our bewitching Moon's unending, gentle tug on the forces of life. In this sense, it may be detrimental to completely dismiss these ancient myths--ascribing them to an unsophisticated and archaic past. Ganymede: Ganymede is both the largest moon of Jupiter, our Solar System's planetary behemoth, as well as the largest moon in our entire Solar system. Observations of Ganymede by the HST in 2015 suggested the existence of a subsurface saline ocean. This is because patterns in auroral belts and rocking of the magnetic field hinted at the presence of an ocean. It is estimated to be approximately 100 kilometers deep with a surface situated below a crust of 150 kilometers. But there is an important difference. On our own planet, lakes and seas are flowing with water, while Titan's lakes and seas are filled primarily with methane and ethane, that slosh around within these liquid reservoirs. In this never-before-seen cycle, the hydrocarbon molecules evaporate and condense into clouds that send an exotic "rain of terror" back down to this strange moon-world's carbon-slashed surface.