when did life begin on our planet?
Four billion years ago
Earth
Chemical reactions led to the first self-replicating molecules about four billion years ago. A half billion years later, the last common ancestor of all current life arose. The evo
where does the sun lie within the milky way galaxy The Sun is near the inner rim of the Orion Arm, within the Local Fluff of the Local Bubble, and in the Gould Belt what is this way exactly? The Milky Way is the galaxy that contains our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye is it visible from our planet? Yes, it is visible from Earth as a hazy band of white light, some 30° wide, arching across the night sky
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Earth [SEP] Origin of life and evolution
Chemical reactions led to the first self-replicating molecules about four billion years ago. A half billion years later, the last common ancestor of all current life arose. The evolution of photosynthesis allowed the Sun's energy to be harvested directly by life forms. The resultant molecular oxygen () accumulated in the atmosphere and due to interaction with ultraviolet solar radiation, formed a protective ozone layer () in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes. True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized Earth's surface.