Just take a look at the age of Adam's bridge :1,750,000 yrs old.In all possibilities,this was Rama's bridge which he created.So say he was 30 yrs of age then,(assume) which wont a difference anyways,we are talking about 1748000 B.C approximately as the real age of Rama Empire.
Now say if life started 3 million years back.And there were Nine Avatars,so,approximately you have 333,333333.3 years for each avatar.So 1st Avatar was from 3 Billion B.C to 2,666,666,667 B.C.Now 2nd avatar was from : 2,666.666.667 to 2,333,333,334 Billion B.C old ; 3rd Avatar was from 2,333,333,334 B.C to 2,000,000,001 B.C,4th Avatar was from 2,000,000,001 to 1,666,666,668 B.C.;5th avatar from 1,666,666,668 B.C to 1,333,333,335 B.C;6th Avatar from 1,333,333,335 B.C to 1,000,000,002 B.C;7th Avatar from 1,000,000,002 B.C. to 666,666,669 B.C. ;8th Avatar was from 666,666,669 B.C. to 333,333,336 B.C and 9th Avatar from 333,333,336 B.C. to 2 B.C.(recently!) and tenth avatar can come upto what 333,333,333 A.D approximately so we have lots of time left.But these calculations are only valid if there was not time lag between those periods PLUS Each period was equal which is highly unlikely.
But since the Rama's bridge was found to be 1,750,000 B.C. there fore we can say that since 1,750,000 years have passed from 333,333,333 years and there was another avatar in between this period which was Krishna's avatar BTW,so our assumption was wrong about time period of each avatar...krishna's avatar period started from say 1,738,000 B.C and ended in the ice ages...
just some random thoughts...
bye!