To recover corals that grew at times when sea level was lower then at present it is necessary to drill into the sea floor at depths of up to 140 meters below sea level.
Two IODP expeditions to Tahiti, French Polynesia, and the Great Barrier Reef, Australia recovered such material.
Where the motion of the land can be constrained, measurements of past sea level markers allow local sea level changes to be determined.
If modern lead, for example, from marine sediments or modern basalts has the composition of lead in the Earth and if the lead in the troilite phase of iron meteorites has the composition of primordial lead, then a simple model yields about 4.6 billion years for the age of the Earth.
This age is in good agreement with the age of the meteorites and the age of the Moon as determined independently.
In both expeditions holes were drilled into the sea bed at a range of depths to recover corals that grew during the rise of sea level from the last glacial maximum (20-26,000 years ago) when sea level was approximately 120 m below present.
In addition to recovering corals that recorded the sea level rise of the last deglaciation, corals were recovered form earlier periods of lower sea level from reefs that were preserved underneath the postglacial sequence.
Uranium-series dating is a critical tool in quaternary geochronology, including paleoclimate work, archaeology and geomorphology.
Laser ablation (LA) methods are not as precise as most isotope dilution methods, but can be used to generate calendar ages rapidly, expanding the range of dating tools that can be applied to late Pleistocene carbonates.
To place these markers in the past, corals also prove particularly well suited.
Their calcium carbonate skeleton offers up the potential for carbon dating (up to 30-40,000 years), because it is 12% carbon.
Each sample analysis lasts for ∼4.3 min, and fifty samples can be measured in 12 h with an automated set up, after a day of sample preparation.
The use of different standard materials and laser systems had no significant effect on method accuracy.
U-series dating of speleothems is also addressed, to allow for expanded discussion of the issues involved in obtaining and interpreting U-series dates of fossil coral reefs.