Why did God create the earth?

God isn't something rational, he is the cause himself. The creation is the beginning of everything, nothing existed before the creation, therefore there couldn't be any reason for the creation. The bible itself starts with the sentence- " In the beginning God created the heaven and the earth". If the creation is the beginning, no event could have occurred before that including any rational process of cause-consequence. The question of "Why god created earh" has no answer from it's very own essence.

The question invites another question, "If there is a landslide in the desert and no one is around, is there a loud noise?" If there were no earth and no people populating it who would be around to recognize the awesome power of God and his creation of the universe?

I think you can find the answer in the Book of Genesis: "God saw all that he had made, and it was very good." (1:31 for example).

The Earth was created because it is good. 

God created the earth to sustain us and demonstrate love to us. He has no need for this planet other than to love us.

God Himself did not create the earth. God is around all things big and small but there are spirits who work at different levels and are responsible for the creation of all things. God as you call the Eternal loving emotion is not a interfering One but exists in all realems. Everything we do is our own responsibility and are accountable for it. The bible is only a guide and no all interpetations are correct.

Almighty God created the earth for it to be lived upon by perfect humans. Though sin entered into the picture from disobedience, the purpose for the earth will still be completed (Isaiah 55:11) and please read Isaiah 45:18 which is a direct answer to your question.