the standards for 'life' (as we know it) are actually fairly low. bacteria count as living. viruses typically don't (though there is a great deal of controversy around whether they are living or not).

someone or other computed some probabilities or other and figured that it would be improbable indeed if we were the only planet with life (as we know it). *intelligent* life though... or *intelligent* (as we know it) life (as we know it) would be super cool... perhaps...