I don't think they are a necessary condition for advanced life. Animal oils, trees and water/wind should EVENTUALLY allow a species to hit our level and more. It would just take a shitload longer because carrying capacity would be much lower and clearly those sources are less efficient. So maybe it takes a species 20,000 years instead of 200.

(http://www.autoadmit.com/thread.php?thread_id=4149257&forum_id=2챦�#37355157)

However, recent developments in biology suggest otherwise. It may be that vast quantities of free oxygen in the atmosphere are commonly a byproduct of the first life forms.

This waste product oxygen is thereafter consumed by more active O2-breathing life that develops in response to all the O2 waste product generated by the earlier co2-dependent life and now free for the taking. And oxygen packs a punch in terms of electrochemical energy that CO2 does not. The extra electrochemical energy that free oxygen provides (that the more commonly found carbon dioxide does not) can be used to power further evolutionary development.

If this pattern of early O2 production followed thereafter by O2-breathing life is a biochemically predetermined step in the evolution of complex life, as the evidence suggests, it may be that in most instances higher life forms, once present, will usually find themselves w ample fossil resources to utilize.

It may be that the Great Filter theory needs some modification.

(http://www.autoadmit.com/thread.php?thread_id=4149257&forum_id=2챦�#37359578)