Free Astronomy Magazine March-April 2015

tween Martian structures and terrestrial struc- tures, definitely related (at least in the case of our planet) to bio- logical activity. On the right, the stretch of Mar- tian surface cov- ered by Curiosity after leaving Yel- lowknife Bay. Currently the ro- ver is scouting the Pahrump Hills. [NASA/JPL- Caltech/MSSS, No- ra Noffke, Univer- sity of Arizona] environmental conditions; both possessed an atmosphere sufficiently dense to protect their surfaces from harmful solar radiations; both had an ex- tensive network of rivers flowing into lakes and seas; both ultimately offered suitable conditions for the development of the most basic forms of life and surely these condi- tions persisted on Mars for several million years. Why life should not therefore have ap- peared also on Mars and gener- ated sedimentary structures similar to those found on Earth? verifications, remain some underlying facts that are now indisputable: about 3.5 billion years ago, Earth and Mars had very similar n MF