Lithosphere: upper part of the solid earth. External energy: radiation from the sun, drives the water cycle and wind cycle. Internal energy: caused within the earth by radioactive decay (e. g. plate movements) Gradual: slow over millions/ billions of years. Rising human pop requires energy and resource consumption. Result: ozone hole, air/ water pollution, deforestation, etc. Universe created by a big explosion: the big bang. Hot clouds of hydrogen and helium formed giving rise to the stars and the planets. Radioactive decay caused melting of the early earth. Leading to internal differentiation: heavy elements (iron, nickel) settled in the inner core, lighter elements settled on the outside forming the mantle. Atmosphere had lots of gases especially co2 (kept the earth warm in the absence of ozone layer) and no oxygen. At 2. 4 bya, first photosynthetic bacteria evolved. Oxygen was entered into the atmosphere; ozone layer formed. Oxygen"s presence significantly decreased sulphur"s presence in the atm.