In particular, they make measurements of a heavy variety, or isotope, of the oxygen atom, as well as measurements of a lighter oxygen isotope. This quantity has been tied to presumed past climate values.If one plots these values on a graph, many “wiggles” are apparent at different depths within a sediment core (Figure 3).

Since they also think some organisms lived only during certain periods of Earth history, they conclude that these fossils can be used to date different rock layers.

For instance, suppose one particular organism has so far been found only in rocks thought to be between 200 and 180 million years old.

Many Christians are reluctant to accept the Bible’s clear teaching of a recent creation because they believe secular dating methods prove that the earth is extremely old.

The apparent agreement between seemingly independent dating methods is seen as a powerful argument for millions of years.

These decreases in sunlight are thought to be caused by slow, gradual changes in the tilt of Earth’s axis and the shape of its orbit around the sun (see the inset in Figure 2).

They think this reduction in sunlight causes the high-latitude ice sheets to increase in size, resulting in an ice age.This kind of circular reasoning is also present in the dating of ice cores and seafloor sediments.Deep Ice and Sediment Cores To study past climates, scientists drill and extract cylindrical rods of ice, known as ice cores, from the Greenland and Antarctic ice sheets.But closer inspection reveals that these methods are not truly independent, and the agreement between them is the result of circular reasoning.Dating Rocks and Fossils: Circular Reasoning Because secular scientists believe Earth’s sedimentary rocks were deposited over millions of years, they assume a given rock layer represents a “snapshot” of the history of life at a certain time in the “prehistoric” past.Likewise, scientists also extract long cores from the ocean floor.