There seems to be a little discussion on this topic so I thought I’d throw in my .02 worth.  <big winkie-winkie/grin>
 
While we don’t know all the facts regarding the pre-adamite life, it is possible there was life on earth before God created Adam.
 
Before going there, to be sure, fallen angels cannot possess or enter into an object, person or animal as demons do.  Demons are disembodied spirits and are the offspring of the intercourse between fallen angels and ungodly women.   When God flooded the earth, wickedness was at all time high because the Nephilim or giants were roaming all over the place. (Genesis 6).
 
When they died, their bodies perished but not their spirits and thus these disembodied spirits are now called demons.  We read Jesus casting out demons but never casting out fallen angels.
 
Fallen angels are described in Ephesians 6:12 as principalities, as powers, as rulers of darkness and spiritual wickedness in high places.  In the Dark spirit world there is a hierchy:  Satan, Fallen Angels, demons.
 
The Prince of Persia described in Daniel was/is a fallen angel.  The angel who came to deliver an answer to Daniel’s prayer, most likely Gabriel, had to ask for Michael’s help to fight that powerful fallen angel.
 
To life on earth before God created Adam, it is possible God had placed Lucifer in charge of it, for in Isaiah he says “ I will ASCEND (go up) into heaven, etc....” From where was he ascending ? When he and the third of the fallen angels were cast out of heaven, Genesis 1:2 describes the earth being void and without form.  God would not have created the earth without form and void, darkness filling the earth!  God is LIGHT.  Lucifer was called ‘son of the Morning’.
 
The scriptures tell us as it was in the days of Noah, so shall it be at the coming of the Son of Man.  There is compelling evidence, Nephilim are trying to inhabit the earth.  Most of the stories and accounts on people being abducted by aliens (fallen angels) I believe are true.  But true Born Again, Blood bought and cleansed believers can not be abducted.  The purpose of these abductions is to create a Nephilim race more evil than the ones during the days of Noah.
 
Recommended books/teachings:
 
The Spirit World by Clarence Larkin
 
Alien Abductions by L.A. Marzulli
 
The Return of the Nephilim by Chuck Missler
 
Hope this was helpful !
 
Carol Garza