Radiometric dating instruments
How do scientists know the bones are really 68 million years old?
Today's knowledge of fossil ages comes primarily from radiometric dating, also known as radioactive dating.
The Christian Creationists have criticized it on the grounds that it is inaccurate.
But these inaccuracies are the result of variation in the level of Carbon 14 in the atmosphere, and when this is worked out (through calibration with tree rings of the bristlecone pine, the oldest living organism) precise dates can be had.
Bishop James Ussher, a 17th-century Irish cleric, for example, calculated that creation occurred in 4004 B. There were many other such estimates, but they invariably resulted in an Earth only a few thousand years old.
By the late 18th century, some naturalists had begun to look closely at the ancient rocks of the Earth.
We usually hear of Carbon 14 dating, which is very important in archaeology.They observed that every rock formation, no matter how ancient, appeared to be formed from still older rocks.Comparing these rocks with the products of present erosion, sedimentation, and earth movements, these earliest geologists soon concluded that the time required to form and sculpt the present Earth was immeasurably longer than had previously been thought.When paleontologist Mary Schweitzer found soft tissue in a Tyrannosaurus rex fossil, her discovery raised an obvious question -- how the tissue could have survived so long?The bone was 68 million years old, and conventional wisdom about fossilization is that all soft tissue, from blood to brains, decomposes.