19th January 2014 Sol 517

On Earth rocks that are as ancient as those we are studying on Mars have been destroyed by the tectonic recycling process or heavily metamorphosed.  Outcrops like this Harrison outcrop have escaped high temperature and pressure alteration and so have preserved their original mineralogy and textures.  The clast arrowed in the middle of the field of view, with light (probably feldspar) and dark minerals may be fragments of the original crust of Mars which formed 4.5 billion years ago.  Fragments were broken up by physical weathering and brought down rivers into Gale Crater.

Thus studying the surface of Mars with Curiosity allows us to look back at the earliest terrestrial crustal formation processes.