Students often have very strong opinions on this matter, and it is a topic that sometimes tests the limits of my promise to avoid getting into partisan politics. Thus, care must be taken at this point in the course to maintain our focus on the scientific rigor regarding what is known about the age of the Earth, geological processes, and evolution, and I try to be careful to maintain appropriate pedagogy. In a controversy such as this one, though, the boundaries between fact and opinion can sometimes blur. I want to, therefore, state my perspective here clearly, but to also remind the reader that this is only my perspective. In class, I try to be careful, here and throughout the course, to present the science as science and to encourage the students to develop their own ideas about incorporating that science into how they make meaning in their lives.
Here is how I see it: Living with uncertainty can, of course, be very challenging. It seems to me that one response some people have to the inability of science to completely eliminate uncertainty is to reject the entire scientific enterprise. This, I think, is the "fuel" for the movement to go back to a pre-science origin story. A great deal of the underlying tension in this controversy, it seems to me, is rooted in fundamental differences in how scientists and non-scientists deal with uncertainty. In a world of uncertainty, people are searching for something to believe in, and if they have a strong need for certainty they are not likely to be comfortable with the culture of science. All scientific conclusions and theories assume some level of uncertainty. A common dismissive response that creationists have to the theory of evolution, for example, is that it is "only" a theory and that it has never been proven. But scientific theories are never "proven." They are never "final" answers, but rather accepted best answers until something better comes along that matches observations better than the previous theory.
The approach to this topic taken in this course is to cover the history of understanding of geological processes and evolution, and to explore in detail how scientists have come to conclude that the Earth is billions of years old. The course goes into quite a lot of detail on the topic of the age of the Earth for three reasons. First, the way that scientists use various approaches (e.g., fossils, rates of deposition of sediments, and radiometric dating) to estimate the age of the Earth is an excellent example of the scientific method and how scientists operate. Second, a full understanding of radiometric dating provides an excellent window into how scientists investigate the way the world works. And finally, evolution takes a lot of time and requires the many millions of years time scale within which to operate. The theory of evolution states that the observed variation in living organisms can be explained by modifications due to slow, but persistent, natural processes continuing over very long periods of time (many millions of years).
This part of the course thus presents the following timeline for how scientists understand the age of the Earth, the age of the Universe, and the timing of human existence within this vast amount of time:
- Big Bang: About 14 billion years ago.
- Age of Earth: 4.6 billion years.
- Modern Humans: Approximately the past few 100s of thousands of years.
- Human Induced (?) Global Warming/Industrial Revolution: A little more than the past 100 years.
