Igneous rocks are made mainly of compounds of
carbon and hydrogen
silicon and oxygen
carbon and silicon
carbon and oxygen

Suggest two reasons why irrigation is important for human development of the desert

1. crust 1 the metallic layer at the earth's center 2. inner core 3 the firm layer between the crust and the asthenosphere 3. lower mantle 2 the layer surrounding the inner core 4. asthenosphere 4 the semi-solid layer between the top layer and the upper mantle 5. upper mantle 5 the layer between the asthenosphere and lower mantle 6. top layer 6 the earth's outermost layer 7. outer core 7 the hottest part of the mantle

During which era in earth's history were the first insects? mesozoic precambrian cenozoic paleozoic