Earth surface observations:

1. Continents — granite — a few 100 meters above sea level — old (up to 4 Ga)
2. Oceans — basalt — about 4.5 km below sea level — young (<200 Ma)

Zonation is chemical and physical: Core: Fe-Ni (inner=solid, outer=liquid)

Mantle: solid but plastic; Mg-silicates (green minerals like olivine and pyroxene)

Crust: solid, made of the minerals Quartz (SiO₂), feldspar (Na,K)Si₃AlO₈ and micas

Minerals: combinations of elements (compounds); rocks: combinations of minerals

Formation of elements and the solar system:

Big Bang (15 Ga ago): formation of mainly H (76%) and He(24%). Clustering into galaxies and into stars — formation of elements in stellar furnaces through fusion processes. Fusion processes up to the formation of the element Fe give off heat (exothermic), heavier elements do not form through fusion. Large stars can get so hot that they explode — supernovas è sprays of neutrons and element creation through neutron capture. The heaviest elements are not stable (radioactive) and these decay to lighter elements (e.g., U and Th go to Pb). We mentioned elements and isotopes: share the # of protons (and electrons) but differ in # of neutrons.

Summary: the elements that make up the inorganic world (rocks) as well the elements that make up water, air and life, are all old and probably recycled before in the interior of old stars. The concept of RECYCLING is not new in this universe!!

H, He — Big Bang

up to ⁵⁶Fe Stellar fusion

⁵⁶Fe to ²⁰⁹Bi neutron capture during supernovas

>²⁰⁹Bi : radioactive and decaying to lighter elements

After 2-3 cycles of stellar element formation, 4.55 Ga: formation of sun and solar system: 4 rocky planets, asteroid belt, 4 gaseous planets and Pluto (+ comet belt somewhere in the back). Venus, Earth and Mars similar in composition and distance from the sun, very different climates.

Meteorites are mainly pieces from the asteroid belt, some from Mars and some from the moon. Special group are the carbonaceous chondrites: primordial material of original "solar composition" (minus H+He) in unprocessed form. They have been floating around since 4.55 Ga and nothing happened to them until they fell here on earth. Other meteorites consist of processed material, similar to chunks of earth.

How did the earth get from a homogeneous ball of such primordial material into an onion of core-mantle —crust? Planetary processing!