Chapter 36: Geochemistry of Théxar

"Théxar is an alchemist. It turns mantle into crust, crust into soil, soil into life. Every atom we carry within us has passed through this forge." — From the treatise "Elements," Guild of Scientists, +2 900 E.U.

Related sections: → see [Ch.12, "Geology"], → see [Ch.19, "Resources"], → see [Ch.04, "Biochemistry"]

36.1 Element Abundance

Element	Crust (%)	Mantle (%)	Planet (avg.)
Fe	5.8	6.5	32.0
O	45.2	44.0	28.5
Si	22.4	22.0	14.0
Mg	4.2	18.0	12.0
Ni	0.08	0.2	4.0
S	0.05	0.3	2.2
Ca	6.8	2.5	1.8
Al	8.2	2.0	1.6
Na	2.6	0.5	0.6
K	2.4	0.3	0.5

36.2 Geochemical Cycles

Carbon Cycle

Reservoir	C mass (Gt)	Flux (Gt/year)	Turnover time
Atmosphere (CO₂)	52 000	—	—
Biosphere	1 200 000	120 (photosynthesis)	10 000 years
Soils	380 000	60 (respiration)	≈6 333 years
Ocean	1 800 000	90 (dissolution)	20 000 years
Crust (limestones)	12 000 000	0.5 (weathering)	24 000 000 years
Mantle	800 000 000	0.2 (volcanism)	4 000 000 000 years

Sulfur Cycle

Reservoir	S mass (Gt)	Feature
Atmosphere (H₂S, SO₂)	12	Volcanism + biota
Biosphere	18 000	S-amino acids
Ocean (SO₄²⁻)	42 000 000	Dissolved
Crust (sulfides, sulfates)	800 000 000	FeS₂, CaSO₄