Ice core dating
The assumed thickness of the annual layers is important because it constrains the annual thickness in the measurements.
The measurements can deviate a little from the assumed annual layer thickness but not by much.
Some scientists believe that if the ice somehow disappeared, it probably would not return in the present climate. Many ice cores have been drilled deep into both the Antarctica and Greenland ice sheets since the 1960s (see figures 12.1 and 12.2).
It is observed today that these ice sheets incorporate dust, acids, pollution, etc. Near the top of the ice sheets, annual layers can be distinguished by measuring the many variables related to the seasons.
It is interesting to note that the Greenland and Antarctica ice sheets may never have grown to their present size, if it were not for the initial thickness of ice at the end of the Ice Age.The difference between the two models becomes more and more significant deeper in the ice core.Because of extreme annual layer thinning at the bottom of the core in the uniformitarian model compared to the creationist model, the uniformitarian scientists may be counting 100 layers that they think are annual.The method of counting annual layers only works with the high accumulation Greenland ice sheet.However, the deep Antarctic ice sheet cores have been dated to over 300,000 years showing multiple ice age cycles.
The main assumption is that the earth is very old — billions of years old. They think the amount of snow and ice added each year is approximately balanced by the ice that is lost by melting and calving of icebergs into the ocean.