The faint young sun paradox describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the sun's output would be only 70% as intense during that epoch as it is during the modern epoch. Water (from the Old English word wæter and the German word Wasser) is a colorless, tasteless, and odorless substance in its pure form that is essential to all known forms of life and is known also as the most universal solvent. ... Earth, also known as the Earth, Terra, and (mostly in the 19th century) Tellus, is the third planet outward from the Sun. ... History Forums - History is Happening -Discuss all historical topics, as well as current events, in an academic setting. ... Spiral Galaxy ESO 269-57 Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature and chemical composition) of astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... A sun is the star at the center of a planetary system. ...

The standard solar model describes the history and evolution of stars. An aspect of this model is that stars similar to the sun should gradually brighten over their life time (excluding a very bright phase just after formation). This prediction is supported by the observation of lower brightness in young stars of solar type. However, with the predicted brightness 4 billion (10⁹) years ago and conditions like the modern Earth, any liquid water exposed to the surface would quickly freeze solid. This contradicts geological observations of sedimentary rocks which require the presence of flowing liquid water to form. The word billion, and its equivalents in other languages, refer to one of two different numbers. ... Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history, and the processes that shape it. ... Two types of sedimentary rock: limey shale overlaid by limestone. ...

Most scientists confronting this contradiction propose that the answer is to posit some form of super greenhouse environment early in the Earth's history. It is possible that outgassing from volcanoes during this period led to extraordinary concentrations of carbon dioxide, methane and other greenhouse gases. Because free oxygen was very rare during this period, these gases may have persisted in the atmosphere for longer than during modern atmospheric conditions. Such greenhouse gases may have increased the impact of the greenhouse effect to levels capable of sustaining liquid water even in the presence of significantly reduced solar input. A greenhouse in Saint Paul, Minnesota. ... A volcano is a geological landform (usually a mountain) where magma (rock of the earths interior made molten or liquid by high pressure and temperature) erupts through the surface of the planet. ... Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. ... The simplest hydrocarbon, methane, is a gas with a chemical formula of CH4. ... Increasing CO2 levels Greenhouse gases (GHG) are gaseous components of the atmosphere that contribute to the greenhouse effect. ... Atmosphere may refer to: a celestial body atmosphere, e. ... The greenhouse effect, first discovered by Jean Baptiste Joseph Fourier in 1824, is the process by which an atmosphere warms a planet. ...

It is also noteworthy, that even though evidence of flowing water exists even from very early in Earth's history, there may still have been a number of examples of periods when the Earth's oceans froze over completely. See: snowball Earth. The most recent such period was ~630 million years ago and may have been instrumental in leading the Cambrian explosion of new multicellural life forms. Ocean (from Okeanos, a Greek god of sea and water; Greek ωκεανός) covers almost three quarters (71%) of the surface of the Earth. ... The Snowball Earth, also known as the Varangian glaciation, is an hypothesis that has been around for several decades but which has recently been reformulated by Paul F. Hoffman, Sturgis Hooper Professor of Geology at Harvard University. ... The Cambrian Explosion is the seemingly sudden appearance of a number of new complex organisms between 543 and 530 million years ago (MYA). ...