Faint Young Sun Paradox

Theories of stellar evolutionChanges in a stars luminosity and temperature over its lifetime; conventionally, plotted on an Hertzsprung-Russell (HR) diagram. All stars, irrespective of their mass spend most of their lifetime on the main sequence. The more massive a star, the more luminous and hotter it is. As all stars age, they enter indicate that as stars mature on the main sequence, they grow steadily hotter and brighter. About the time of the formation of Earth (~4.56 Ga), the Sun’s luminosityBasic property used to characterize stars, luminosity is defined as the total energy radiated by a star each second. An object’s luminosity is often compared to that of the Sun (Lsun = 4 × 1033 ergs/s = 3.9 × 10 Watts). Luminosity has the same units as power (energy per was roughly two-thirds its present value; the surface temperature of early Earth would have had a mean temperature of -15 °C (258 K). However, there is no geological evidence on Earth for a cooler SunOur parent star. The structure of Sun's interior is the result of the hydrostatic equilibrium between gravity and the pressure of the gas. The interior consists of three shells: the core, radiative region, and convective region. Image source: http://eclipse99.nasa.gov/pages/SunActiv.html. The core is the hot, dense central region in which the. For example, there is evidence of liquid water on Earth as early as ~4 Ga. To resolve this disparity, it is often proposed that Earth’s greenhouse effect was greater early in its history (probably enhanced by high concentrations of methane, CH4). Indeed the Gaia hypothesis argues that the Earth’s temperature has been regulated by life throughout its existence.

The paradox less easily resolved in the case of Mars, which has features like those produced by running water, but would have had a mean temperature of -77 °C (196 K). It is possible the fluid eroding martian channels was not water but instead fluidized avalanche debris (a mixture of dust, rocks, and ice) supported by CO2 vapor and no unusual past climate needs to be invoked.