Evidence is found in the half-life of materials; it's found in DNA.
Dr. Ross Olson's "The evolution of a creationist" (Aug. 1) contained several passages that were presented as serious science. They are not; they are religious views. Olson is very much entitled to express his religious views, but when he uses scientific arguments to support them, he invites scientific scrutiny. And science has much to say about evolution and the age of the Earth.
Radiometric dating of rocks has long been accepted practice. Certain types of atoms decay at measurable rates; this is the famous "half-life" of materials. For example, uranium has a half-life of 4.47 billion years. This means that if you possess a chunk of uranium, in 4.47 billion years half of its atoms will have decayed into lead and a few other metals. Rocks containing uranium have been examined and have consistently been found to have lead-to-uranium ratios matching an Earth about 4 billion years old.
Evolution implicitly requires huge amounts of time. For one species to change into another, enough DNA mutations must occur so that one group of animals becomes two. In rare cases this can occur in a few thousand years, but hundreds of thousands of years are usually required. What's more, the evidence of these splits is written in our DNA. The sequences we share with the other great apes demonstrate that they and we descended from a common ancestral group. We can even determine roughly when that group split by comparing our DNA.
This technique has been applied to the whole tree of life, and the evidence strongly points to a common ancestor about 3.8 billion years ago, matching the radiometric data. This isn't just an ancestral animal. This ancestor is common to every living thing. It ties us to bacteria, apple trees and even flies.
The preserved Tyrannosaurus rex that Olson mentions is a fascinating case. The original paper claims to have found preserved soft-tissue structures in the bone. While that finding is somewhat controversial, in other dinosaur fossils soft tissues have been indisputably preserved. When those tissues are examined, they clearly are made of the same stuff that animal bones are made of now. Even their hemoglobin, the molecule that lets blood carry oxygen, is very similar to that in living animals.
This is exactly what we would expect if all animals were descended from a common ancestor. However, the idea that humans and dinosaurs lived simultaneously is unsupported. We know from fossil, molecular and much other evidence that humans arose no more than one million years ago, and dinosaurs died out 65 million years ago. Interestingly, we still share the Earth with their lineage. The only difference is that they have now evolved into birds.
When doing science, evidence must be accumulated that supports a given hypothesis. If the data do not fit that hypothesis, then the hypothesis is wrong and it must be set aside. Olson claims that evidence disproving evolution has been swept under the rug. This is untrue.
Our current understanding of evolution, called the modern synthesis, is a mighty fortress of scientific achievement. Decades, careers and whole lives have been devoted to building it, and it has withstood all challenges. The evidence is quite clear. The Earth is ancient, life on it is ancient, and life has come to be through evolution.
Luke Streich, of Golden Valley, studies molecular biology at Northwestern University.
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