About six weeks ago, Dr. Tara Harmer was aboard a research vessel and took part in a submarine dive to the bottom of the Pacific Ocean. But years before that, she was a student in the Hermitage School District.

Dr. Harmer, a post-doctorate fellow in the biology department at Harvard University in Cambridge, Mass., on Friday visited Delahunty Middle School to show students slides from her excursion on the research vessel Atlantis and the submarine Alvin. The R.V. Atlantis and Alvin both belong to the Woods Hole Oceanographic Institution in Massachusetts.

When Dr. Harmer came to the school, she brought with her foam cups the sixth grade students had decorated and mailed to her several months earlier. She took them in the submarine with her, and the pressure change in the submarine shrunk them to a fraction of their sizes.

Dr. Harmer attended Hermitage schools until she was in eighth grade, when her family moved to New Jersey. She studied marine biology at Boston University and molecular biology at Johns Hopkins University in Maryland before beginning her post-doctorate work at Harvard.

When she was in sixth grade, Dr. Harmer wanted to be an astronaut. But after a trip to Wallops Island in Virginia, where members of the QWEST program still go every spring, she became interested in marine biology.

"People know more about the surface of the moon than the surface of the sea floor," she said. "Exploring the deep sea is a lot like exploring space."

During her studies, Dr. Harmer developed an interest in symbiosis, which is when two separate organisms live together and benefit each other.

On her excursion, she studied giant tube worms, which live on the ocean floor. The tube worms don't have mouths and don't eat; bacteria living inside them release chemicals that nourish them. The process is called chemosynthesis, which is similar to photosynthesis, the process in which plants use light to create food.

Dr. Harmer said she is studying those bacteria and how they get inside the worms. When the worms are born, they have mouths and swim through the water to get food. When they get older, they attach themselves to rocks and remain stationary, obtaining their nutrition from the bacteria.

"We know that bacteria has to come from somewhere," she said. "We're looking for the bacteria outside of the worms."

Dr. Harmer departed a few days before Thanksgiving from Costa Rica and returned the day before Christmas. The QWEST students tracked her journey on the Internet.

During the month-long trip, Dr. Harmer took part in one dive in Alvin, the submarine that discovered the Titantic. The submarine carries three people -- two scientists and the pilot -- and takes about an hour and a half to submerge to the ocean floor. The scientists spend about eight hours in the submarine before returning to the surface.

Before anyone goes on a dive, they must be fitted with an oxygen mask. Anyone who does not have a properly fitting oxygen mask cannot dive, because the masks would be crucial to survival if fire broke out on the submarine, Dr. Harmer said.

Everyone on the ship must also have an exposure suit to keep warm in case the ship sinks. Although the ship traveled in tropical waters of 70 to 80 degrees, prolonged exposure could lower the body's temperature, Dr. Harmer said.

While sailing on the open sea, the crew saw nothing except a few birds, flying fish, some dolphins and a few turtles. Some birds traveled with them on the ship, Dr. Harmer said.

As part of the expedition, Dr. Harmer's research team discovered a new hydrothermal vent, an area in which gases escape from the ocean floor. The vents are similar to underwater volcanoes and spill lava on the ocean floor, which then becomes basalt rock. The giant tube worms live on this volcanic rock.

The submarine had cameras on its outside and collected samples from the ocean floor with a mechanical claw. Although the scientists brought many animals up to the ship with them, such as the tube worms and crabs, most died with hours or days because they could not handle the air pressure at the surface.

Dr. Harmer spoke with QWEST students from Hermitage, Sharon and Farrell in the morning and to the rest of the students at Delahunty in the afternoon. The students' questions varied from inquiries about her research to how the scientists went to the bathroom on the submarine.

Dr. Harmer plans to go on another month-long trip on a research vessel this November.