I have only self-studied logic a little bit, but let me take a stab at this.
First, let's review some terminology. (Source: The Power of Logic ISBN-9780078038198)
A deductive argument is one in which the premises are intended to guarantee the conclusion.
An inductive argument is one in which the premises are intended to make the conclusion probable.
Deductive arguments can be valid or invalid. A valid argument is one in which it is necessary that, if the premises are true, then the conclusion is true. An invalid argument is one in which it is not necessary that, if the premises are true, then the conclusion is true. A valid argument can have true premises and a true conclusion, false premises and a false conclusion, false premises and a true conclusion, or an unknown truth value. The one thing that a valid argument cannot have is true premises and a false conclusion. An invalid argument can have any of the above, even true premises and a true conclusion.
A sound argument is a valid argument that has all true premises.
A good lawyer should be able to construct a valid argument. But the soundness of his argument is determined by the jury. His argument will only be sound if all of its premises are true.
A strong argument is an inductive argument for which it is probable (but not necessary) that if the premises are true, then the conclusion is true. A cogent argument is a strong argument in which all of the premises are true. Note that a cogent argument can have a false conclusion.
To commit a fallacy in logic, is to construct an invalid argument. Wikipedia has a good list of over 50 fallacies.
Let's rewrite the argument in question into a well-crafted form.
- If the earth and the laws of physics allow humans to exist, then God must exist.
- The earth and the laws of physics allow humans to exist.
- Therefore, God exists.
This argument appears to be a substitution instance of the valid form called modus ponens. Therefore, it is formally valid. If its premises are true, then its conclusion must be true. In your opinion, you may affirm that the argument--although valid--is unsound, arguing (most likely) that the first premise is false.