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There is clearly a difference between the calcium content of wood during the wet and dry seasons that compares favorably with carbon isotope measurements. The calcium record can be determined in one afternoon at the synchrotron lab compared with four months in an isotope lab. In the tropical rain forest, relatively few species of trees, such as teak, have visible annual rings.The difference between wet and dry seasons for most trees is too subtle to make noticeable differences in the cell size and density between wet and dry seasonal growth. The story of how humans spread across the globe is constantly being rewritten.
Their team used X-ray beams at the Brookhaven National Synchrotron Light Source to look at calcium taken up by cells during the growing season. Wolffia using a increment borer to age-date an old sierra juniper (Juniperus occidentalis var.australis) on a steep 9,000 foot ridge of Pine Mountain in the San Gabriel Range of southern California.Since the rings are so close together, they must be counted under a dissecting microscope.Three wood cylinders (cores) extracted from the trunk of an old Sierra juniper (Juniperus occidentalis var. Core A has 325 rings, B has 362 rings and C has 412 rings.