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

2. 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?

3. 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.

4. 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

5. 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

6. 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

7. 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.

8. 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

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

10. 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

11. 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.

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

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

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

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

16. 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

17. 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

18. 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?

19. 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

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

21. 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) NH3(g) ∆H = –92 kJ/mole

22. The nitrogen cycle

23. 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

24. 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.

25. 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.

26. 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.

27. 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