Field Trip - Na Federation series, #1

In 1973, five college graduate students accidentally stumble on information in a file folder that leads them to discover that Earth is in contact with an alien race called the Na. The alien peaceful contact mission to Earth is abruptly abandoned to investigate the strange loss of communications with a joint Human-Na science team on a remote planet called Origin. To avoid government prosecution and imprisonment for discovering this secret, Lawrence McAllister and his four friends are maneuvered into joining the Na search party headed to Origin to locate the missing Na and Earth scientists, one of whom is Lawrence's older, smarter and well-regarded brother.
Arriving at Origin the Na discover that an old enemy from their past, a race they call the Amph, who was thought to have been destroyed, have reappeared. While the Humans and Na search Origin for the missing science team, an asteroid, guided by the Amph, impacts the planet with devastating results. Lawrence's group is challenged and threatened at every turn, and must use their knowledge of science, art and history to survive.
Back on Earth, an ancient Amph spaceship has been discovered submerged in the Persian Gulf. With the Na obsessed by their desire to destroy the Amph once and for all, they decide to make an extremely risky, experimental attempt to travel back in time and space to Earth and ancient Sumeria to discover why the Amph hid a spaceship there 5, 000 years ago. What they find, among the beginnings of human civilization, will force Lawrence and his friends to make some cataclysmic decisions that will change their lives forever.