Paleo Slide Set: Coral Paleoclimatology:Natural Record of Climate change for High School Student
Extracting core with hydraulic drill on a Porites lobata colony, Clipperton Atoll.

Scientists take samples from the center of the coral. Here is a slide of scientists taking a core sample. 
With a hydraulic drill connected to a compressor on a boat, they begin to take their core. The most important
part of the drilling process is getting a core that follows the coral's axis of maximum growth. A coral's 
structure is very similar to an onion when sliced in half. If you wanted to drill into an onion to sample as 
many rings as possible, you would cut the core from the top directly towards the center. Drilling at right 
angles to growth bands is how scientists go about getting as long of a sample as possible from each coral. 

Photo Credits:
Maris Kazmers 
SharkSong Photography, Okemos, Michigan