CO2 in the biosphere

At 464ºC Venus is the hottest planet in the Solar System, although it is twice as far from the Sun as Mercury. This extreme temperature is due to an atmospheric composition with 96% CO2, which causes an infernal greenhouse effect. On the other hand, the Earth has 0.04% of CO2 and an average temperature of 15ºC, consequently water is found in the three states (solid, liquid and gas) and life has been given. CO2 is an essential gas for the biosphere for two reasons: it regulates the temperature of the planet and allows photosynthesis of plants. Without CO2 the average temperature of our planet would be 0ºC and life would not be as we know it. During the last 2.5 million years the Earth has experienced the alternation of glacial periods with interglacials in which self-regulation mechanisms have been established. With the burning of fossil fuels, humans have altered the atmospheric composition and have jeopardized the planetary equilibrium.