Crust (geology) magma ocean and floated to the top; however, it is unlikely that Earth followed a similar pattern, as the Moon was a water-less system and Earth had water. The Martian meteorite ALH84001 might represent primary crust of Mars; however, again, this is debated. Like Earth, Venus lacks primary crust, as the entire planet has been repeatedly resurfaced and modified. Secondary crust is formed by partial melting of silicate materials in the mantle, and so is usually basaltic in composition. This is the most common type of crust in the Solar System. Most of the surfaces of Mercury, Venus, Earth, and
Geology of the Iberian Peninsula in the study of geology in Spain. In 1972 the MAGNA plan was created to produce 1:50000 scale maps of Spain (this work began in Portugal in 1952). Between 1986 and 1987 a Spanish-French collaboration called ECORS-Pirineos made a seismic vertical reflection profile 250 km long through the Pyrenees. By 2000 there were six seismic profiles through the Pyrenees which provided a wealth of information of the thickness of the crust and the internal structure of the orogen. Between 1852 and 1857, Carlos Ribeiro made a geological map at 1:480 000 scale of the Portuguese region between the Douro and