The Chemistry of the Earth CHAPTER 19 The Chemistry of the Earth 19.3 Chemistry of the Land

Do we know what the inside of the Earth looks like? We know that a peach is not homogeneous inside Do we know what the inside of the Earth looks like?

What we think of as “land” is just the crust. The inner core is the center of the Earth, where temperature and pressure are very high.

Earth’s crust The two most abundant elements, O and Si, form a class of compounds called silicates Eight elements make up 98.5% of the crust Silicates make up most of the different types of rocks and minerals on Earth

Underground activity Although the surface of the earth appears to be still, there are large scale motions of the crust and upper mantle Volcanoes show evidence of underground activity

Magma is molten rock found below the surface of the upper mantle Magma is molten rock found below the surface of the upper mantle. It contains suspended crystals and dissolved gases. Volcanoes show evidence of underground activity

Lava is molten rock or magma released from the vent(s) of a volcano. As it cools, it crystallizes to form igneous rock. Igneous rock covers more than 90% of Earth’s crust.

If only eight elements make up 98 If only eight elements make up 98.5% of Earth’s crust, and most of it is igneous rock, where does the diversity of rocks and minerals come from? Feldspar Quartz

mineral: a natural nonorganic solid with a definite chemical formula, typically crystalline in structure. rock: a mixture of minerals. Feldspar Quartz

Effects of pressure and temperature Atoms are arranged differently: Carbon atoms in a trigonal planar arrangement form graphite Carbon atoms in a tetrahedral lattice form diamond Diamond Graphite

Effects of composition Effects of pressure and temperature Atoms are arranged differently Effects of composition The melting temperature will vary: Low-silica lavas solidify more slowly and travel farthest Basalt is a low-silica type of lava, with of 45-50% SiO2.

The rock cycle Different types of rock on Earth are interconnected sedimentary rock: rock formed from the compression of small pieces of igneous rock.

The rock cycle metamorphic rock: rock created from igneous and sedimentary rock under conditions of heat and pressure.

Rock tells a story about Earth that reaches far beyond our human history record.

The rock cycle The different kinds of rocks and minerals in Earth’s crust come from magma or molten rock.

We have seen that both animals and plants need to make amino acids Amino acid structure They need to access nitrogen to do this The backbone of all proteins require the presence of nitrogen

We have seen that both animals and plants need to make amino acids Nucleotide structure Animals and plants also need nitrogen to build DNA molecules Nitrogenous bases in DNA require the presence of nitrogen

946 kJ/mole to break N–N bond The triple bond in N2 requires a lot of energy to break. How can living system access this nitrogen source?

946 kJ/mole to break N–N bond The nitrogen cycle Atmospheric nitrogen fixation There is enough energy to break the N–N bond when lightning reacts with the air. NO3– and NO2– are formed, and enter the nitrogen cycle. 946 kJ/mole to break N–N bond

The nitrogen cycle Bacterial nitrogen fixation Some bacteria contain a nitrogenase enzyme capable of breaking the N–N bond.

The nitrogen cycle Production of synthetic fertilizers With a growing population, we need more fertilizer than can be produced by nature alone. The Haber-Bosch process takes nitrogen gas from the atmosphere and makes liquid ammonia. This reaction takes place under high pressure and in the presence of a catalyst: N2(g) + 3H2(g) 2NH3(g) ∆H = –92 kJ/mole

The nitrogen cycle

Phosphorus Living systems also need phosphorus Nucleotide structure ATP molecule The ATP molecule carries energy in the bonds between phosphate groups The DNA backbone relies on the phosphate group of nucleotides

The phosphorus cycles The phosphorus cycle is also a chemical process. Notice that the phosphorus does not come from the atmosphere, but cycles among land, the ocean, and living systems. The phosphorus cycle is also a chemical process.

Soil chemistry Soil is a mixture of: - minerals (inorganic solids) - organic matter (living microorganisms, and decaying plant and animal matter) - water - air The soil that develops over time is influenced by climate, types of minerals in the soil, organisms living in the soil, and the geography of the land itself.

Soil chemistry The pH should be 6 – 7.5 The pH of the soil influences the plant’s ability to take up nutrients from the soil. The pH should be 6 – 7.5 If the pH is too high, ions form precipitates and cannot be absorbed by the plant. If the pH is too low, nutrients can be leached from the soil.

The nitrogen cycle The phosphorus cycle Soil chemistry The nitrogen in the atmosphere becomes available to living system through: - atmospheric nitrogen fixation - bacterial nitrogen fixation - production of synthetic fertilizers Phosphorus does not come from the atmosphere, but mostly from rocks and minerals in the soil. Soil chemistry Plants need a specific pH range in order to uptake nutrients efficiently