Identify the formal fallacy committed in the following argument: 'One way humanity could die out is, if the Sun stopped functioning then we would surely go extinct. If we all go extinct it must have been because our Sun stopped working.'

The argument commits the fallacy of affirming the consequent.

The conditional says if the Sun stops functioning, then humanity goes extinct.

It then observes the consequent, that humanity has gone extinct.

From this it wrongly concludes the antecedent, that the Sun must have stopped.

Affirming the consequent to reach the antecedent is an invalid conditional form.