WHY WE ARE GETTING PAGE SCAN SPIKES AND ORACLE MEMORY FAR EXCEEDS THE ALLOCATED 8GB?

Database version 10.2.0.3

Platform Sun Solaris

Used memory exceeds sga_target and sga_max_size settings of 8Gb but, the server has always been rebooted - short on memory -

SQL> show parameter sga
------------------------------------ ----------- ------------------------------
lock_sga                             boolean     FALSE
pre_page_sga                         boolean     FALSE
sga_max_size                         big integer 8G
sga_target                           big integer 8G

SQL> select name,value from v$pgastat;
---------------------------------------------------------------- ----------
aggregate PGA target parameter                                   6442450944
aggregate PGA auto target                                         402653184
global memory bound                                               644239360
total PGA inuse                                                  1.0365E+10
total PGA allocated                                              1.0594E+10
maximum PGA allocated                                            1.0778E+10
total freeable PGA memory                                          16121856