Cosmic abundance (by number) Element Abundance (per 100,000) Common molecules H 92,700 H2 (He) 7,200 O 50 H20 (Ne) 20 N 15 NH3 C 8 CH4 Si 2 Mg2SiO4 Mg Fe 1 Fe3O4

Condensation by temperature Condensation temperature Materials Examples 1400-1700 K Ca Al Ti compounds Al2O3 CaTiO3 refractory elements common elements 1300-1400 K Mg, Si compounds Mg2SiO4 MgSiO3 1350 K metallic iron alloys Fe 370 K magnetite Fe3O4 180 K water ice H20 volatile Elements 130 K ammonia hydrate NH3·H20 40-80 K methane, methane ices CH4 CH4·7H20

Migration

Elemental abundance (by number) Universe Element Abundance (per 100,000) H 92,700 (He) 7,200 O 50 (Ne) 20 N 15 C 8 Si 2 Mg Fe 1 Human body Element Abundance (per 100,000) H 60,563 O 25,670 C 10,680 N 2,440 Ca 230 P 130 S

Carbon-silicate cycle and climate stabilisation Walker et al. 1981

Habitable zones

Earth spectrum Selsis

Detecting life? Selsis 2007

A search for life on Earth Sagan et al, 1993, Nature 365, 715

Vegetation Red Edge Sagan et al, 1993, Nature 365, 715

Earth transit transmission spectroscopy Kaltenegger et al 2008

Darwin, ESA

Aim of Darwin is to select light from earth-like planet in the habitable zone, take a spectrum, and search for biomarkers, ozone in particular. Darwin, ESA