I am not sure I agree. WIthout going out on a limb and allowing an exotic explanation, we do know what allows the mechanics of life to operate. We have quite and array of life here, with Cephalopods we have an example of one good alternative to our system, they use hemocyanin, a copper-containing protein, rather than hemoglobin, to transport oxygen. Silicone has also been studied as an alternative to carbon based existence, and also found wanting:
The absence of silicon-based biology, or even silicon-based prebiotic chemicals, is also suggested by astronomical evidence. Wherever astronomers have looked – in meteorites, in comets, in the atmospheres of the giant planets, in the interstellar medium, and in the outer layers of cool stars – they have found molecules of oxidized silicon (silicon dioxide and silicates) but no substances such as silanes or silicones which might be the precursors of a silicon biochemistry.
Link - Silicone Based Life
For life to form, again, as we know it, and under the conditions of an earth like planet, there seems little wriggle room outside of carbon based life, suggesting an identical beginning. Environment would shape the inhabitants to a large extent, but that puts us back with the standard evolutionary model, and with many examples of convergent evolution taking place amongst our 50 billion species, it stands to reason the same would happen on any one of the many earth like planets, offering a similar path to intelligence. I cannot see how one can rationalise life outside of this model without any examples, particularly when nature has had 50 billion of them to experiment with on or own planet unless invoking the great unknown as do the proponents that equate UFO to ET?