Believe it or not there is an answer to this question. There are specifically 2 reason's for us being here on Earth. Both of them deal with where we came from and where we are going, so if you haven't checked out my blog, "God's Plan For You:We Lived Before This" it will help you understand this blog. So the first reason I will explain for us being here is the objective to get a body.
You may wonder, why would getting a body be a reason for us being here, well if we remember God has a corporeal body, or a tangible physical body. And we wanted, in the pre-earth life, to be like our Father and get a body just like His. So He prepared a way for that to happen. Adam and Eve were introduced to the world and with their transgression those spirit's from Heaven were now able to receive their bodies. We have our bodies here on Earth and they will be with us in the next life because of Jesus Christ's Atonement.
The other reason we are here is to progress in righteousness. We are here to be tested and to see if we will obey God's commandments at all costs. We are faced with trials and obstacles everyday so that we can become stronger in our faith and our relationship with God. God said to Jesus Christ after creating the Earth," And we will prove them herewith, to see if they will do all things whatsoever the Lord their God shall command them..." Unfortunately we all mess up and make mistakes, hence the Roman's scripture,"For all have sinned, and come short of the glory of God; being justified freely by his grace through the redemption that is in Christ Jesus:" Clearly we all have fallen short of the glory of God and are not qualified to enter into the presence of God and abide with Him through all eternities, but there is hope and help that would allow us to overcome sin and death. And that is... through the atoning blood of the Good Shepherd, even Jesus Christ.