Life on Earth
Earth formed around 4.54 billion years ago, approximately one-third the age of the universe, by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere and then the ocean, but the early atmosphere contained almost no oxygen. The earliest life forms we know of were microscopic organisms (microbes) that left signals of their presence in rocks about 3.7 billion years old. The signals consisted of a type of carbon molecule that is produced by living things. Oxygen is the gas that is required for the life of most creatures. This is present in the Earth's atmosphere and also in water. Oxygen is constantly put into the atmosphere by plants and trees. Earth's atmosphere also contains a small amount of carbon dioxide. I n March 2017, putative evidence of possibly the oldest forms of life on Earth was reported in the form of fossilized microorganisms discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec,