Why did God create dinosaurs, and then kill them?

The dinosaurs thrived for 250 million years on Earth. If God created them, and then later decided to destroy all of them, what will He do when He tires of us? The dinosaurs represent a kind of race which permeated and controlled the world in complete domination. They existed in perfect balance as their 250 million years attests to. So why were they eliminated. If an asteroid struck earth and destroyed them--it is still by God's hand. If there is no God, and life forms on earth are random and meaningless, where does that leave the human race. We may not need to destroy ourselves with our own bombs. For if we are valued as highly as the race of dinosaurs, which once completely dominated the planet, then we are doomed either way, and we may be discared by whatever power began it all, when that power is sick of us, and longs for something new. Discarded the way we flush a gold fish down the toilet when we are tired of caring for it. What do you think about this idea?