<Table> Composition of Earth's mantle in weight percent <Tr> <Th> Element </Th> <Th> Amount </Th> <Th> </Th> <Th> Compound </Th> <Th> Amount </Th> </Tr> <Tr> <Td> O </Td> <Td> 44.8 </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> Mg </Td> <Td> 22.8 </Td> <Td> SiO </Td> <Td> 46 </Td> </Tr> <Tr> <Td> Si </Td> <Td> 21.5 </Td> <Td> MgO </Td> <Td> 37.8 </Td> </Tr> <Tr> <Td> Fe </Td> <Td> 5.8 </Td> <Td> FeO </Td> <Td> 7.5 </Td> </Tr> <Tr> <Td> Ca </Td> <Td> 2.3 </Td> <Td> Al O </Td> <Td> 4.2 </Td> </Tr> <Tr> <Td> Al </Td> <Td> </Td> <Td> CaO </Td> <Td> 3.2 </Td> </Tr> <Tr> <Td> Na </Td> <Td> 0.3 </Td> <Td> Na O </Td> <Td> 0.4 </Td> </Tr> <Tr> <Td> </Td> <Td> 0.03 </Td> <Td> K O </Td> <Td> 0.04 </Td> </Tr> <Tr> <Td> Sum </Td> <Td> 99.7 </Td> <Td> Sum </Td> <Td> 99.1 </Td> </Tr> </Table> <Tr> <Th> Element </Th> <Th> Amount </Th> <Th> </Th> <Th> Compound </Th> <Th> Amount </Th> </Tr> <Tr> <Td> O </Td> <Td> 44.8 </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> Mg </Td> <Td> 22.8 </Td> <Td> SiO </Td> <Td> 46 </Td> </Tr>

What is the mantle and describe its characteristics