Missouri State University
Dr. Jim Miller

Dr. Jim Miller

  • Professor emeritus of geology
  • Springfield, Missouri

Redefining history: Determining where time periods actually lie

Most people know about the major prehistoric eras, such as the Jurassic Period. But have you heard of others, such as the Cambrian or the Ordovician?

Dr. Jim Miller, professor emeritus of geology, is a member of an international research group that recently redefined the boundary between these two time periods.

“These periods had previously been defined in the 1800s, just not very well,” said Miller. “So in 1974 when I first came to Missouri State, I was appointed as the only voting member of this group that studied the particular group of microscopic fossils—conodonts—which eventually were used to define the boundary between the two periods.”

Layers and layers

In 1995, after years of international travel and examination, Miller suggested a particular genus of conodont to define the boundary. The group agreed, and in 1999 an official section was selected for the base of the Ordovician Period. Sections are vertical sequences of rock that include the particular interval of interest. When one is “selected,” it is used as the standard to compare with other layers of the same time period.

“I had nominated a sequence of rocks I’d studied with many other colleagues in western Utah,” said Miller. “The group eventually picked a sequence of rocks exposed along the coast of eastern Newfoundland in Canada to be the world type section for this boundary. All of this was done using the fossil I suggested and that four other colleagues and I named.”

This type of section is known as a Global Stratigraphic Section and Point, or GSSP. Over the next decade, it was proposed that there should be backup sections to the world type sections for boundaries between periods of the Geologic Time Scale.

“People studying other boundaries in other geologic periods thought that one world locality wasn’t enough, so they suggested creating an ASSP, or Auxiliary Stratigraphic Section and Point,” said Miller. “For example, in this Newfoundland section these rocks were deposited at the bottom of the continental slope in thousands of feet of water. Having an auxiliary point would provide researchers working on shallower marine strata much easier access to a standard for comparison.”

Digging deeper

The photo in Utah taken by Dr. Miller that was selected for a geology book cover.

In June of 2015, Miller attended an international conference focused on the Ordovician Period, and he proposed his Utah section as an auxiliary point. Before then, there had been no suggestions for an ASSP. Miller’s section, after much deliberation and paperwork, was approved.

“It was like winning the silver medal at the Olympics,” said Miller. “It’s an important section. We’ve got nearly 50,000 identified fossils from a sequence of limestone that’s 800 feet thick. Most of those fossils are my conodonts. It’s an important accomplishment that can be used by geologists all over the world.”

Thirst for knowledge

Though Miller has been retired for more than eight years, he remains busy visiting his many sections in Utah and studying the samples he and his team collect there. Miller receives generous support from the department of geography, geology and planning, the dean of the College of Natural and Applied Sciences, the office of international studies and the provost. He looks forward to continuing to visit Utah annually and discovering the history that lies in the rock there.

“It relates back to something I learned from my ninth grade English teacher. She went up to the blackboard one day and said, ‘Imagine that this blackboard represents all knowledge.’

She took a piece of chalk, drew a little circle and whitened it in. She said, ‘Of all this knowledge, this is your circle of knowledge. The perimeter of the circle is where your knowledge impinges on your area of ignorance. That’s how much of your ignorance you’re aware of.’”  

“Then she said, ‘As you increase your circle of knowledge,’ and she made the circle bigger and whitened it in, ‘The perimeter of the circle gets bigger and you become increasingly aware of all you don’t know.’

It’s a really good analogy and ties in with my research. The more I learn, the more I realize there’s a lot I don’t know.”