<Tr> <Td> 23 </Td> <Td> 37 </Td> <Td> rubidium </Td> <Td> Rb </Td> <Td> 300 </Td> <Td> 90 </Td> <Td> 60 </Td> <Td> </Td> <Td> 90 </Td> <Td> </Td> </Tr> <Tr> <Td> 24 </Td> <Td> 28 </Td> <Td> nickel </Td> <Td> Ni </Td> <Td> </Td> <Td> 80 </Td> <Td> 90 </Td> <Td> 190 </Td> <Td> 84 </Td> <Td> 2,250,000 </Td> </Tr> <Tr> <Td> 25 </Td> <Td> 30 </Td> <Td> zinc </Td> <Td> Zn </Td> <Td> </Td> <Td> 75 </Td> <Td> 79 </Td> <Td> </Td> <Td> 70 </Td> <Td> 11,900,000 </Td> </Tr> <Tr> <Td> 26 </Td> <Td> 29 </Td> <Td> copper </Td> <Td> Cu </Td> <Td> 100 </Td> <Td> 50 </Td> <Td> 68 </Td> <Td> </Td> <Td> 60 </Td> <Td> 19,400,000 </Td> </Tr>

What are the 4 most common elements on earth