Model theoretic answer for having algebraic closure

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I am beginner at the model theory and I learn compactness theorem at the class and I saw some application of it and one of them is that "every field has an algebraic closure". How can I prove it with compactness theorem ?

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Given a field $F$, start by using the compactness theorem to show that there exists a field extension $F^*$ of $F$ such that every nonconstant polynomial in $F[x]$ has a root in $F^*$. (When applying compactness, you should be considering a theory over a language that includes constants for the elements of $F$.)

What happens when you iterate this process?