Mars O2 = 0.13% N2 = 2.7% CO2 = 95% -47oC
	Earth O2 = 21% N2 = 79% CO2 = .03% 17oC
	Venus O2 = 0% N2 = 1.7% CO2 = 98% 477oC

Goldilocks And The Three Atmospheres

Atmospheric differences among the inner planets are influenced jointly by their proximity to the Sun and individual aspects of their evolution. Earth is our solar system's "Goldilocks": Venus is too hot; Mars is too cold; Earth is just right. One of the big questions is: Why are the inner planets, so similar in origin and relative composition of elements, so different? What accounts for the strange nature of Earth's atmosphere?

Life makes the difference. Carbon-dioxide-consuming and -producing beings of the biosphere, tightly coupled with geological processes, have influenced Earth's faces and flows for thousands of millions of years.

Planetary Atmospheres

Percent by weight of oxygen, nitrogen, and carbon dioxide.

Mean annual surface temperature in ^o C.

Global temperature, gaseous atmospheric composition, and oceanic salinity and alkalinity fall under active biological modulation. Chemical, geological, and geophysical forces influence our environment. The biosphere forms a living body, an aggregate of interactive Earth. (Illustration adapted from graphic by Jesse Anderson, courtesy New England Science Center)