<Tr> <Th> Most Abundant Elements of Earth's Crust </Th> <Th_colspan="1.5"> Approximate% by weight </Th> </Tr> <Tr> <Td> O </Td> <Td> 46.6 </Td> </Tr> <Tr> <Td> Si </Td> <Td> 27.7 </Td> </Tr> <Tr> <Td> Al </Td> <Td> 8.1 </Td> </Tr>

Where is the maximum thickness of crust found and why