Carl R. Woese, 84, a scientist at the University of Illinois who provided a new way of classifying living things that offered insight into the process of evolution, died of pancreatic cancer Dec. 30 at his home in Urbana, Ill. The Institute for Genomic Biology at the university announced his death.

Through his pursuit of fundamental distinctions within major realms of the living world, he painted a new portrait of the tree of life, separating it into three main branches instead of two, and winning a reputation as a scientific visionary.

In 1977, Dr. Woese (pronounced WOHZ) and several colleagues published a paper hailed as one of the most far reaching in the field of evolution since Charles Darwin revolutionized biology in the 19th century. It was credited with offering a means for applying evolutionary theory to the earth’s teeming population of microbes.

He “rewrote the textbooks,” said Gene E. Robinson, director of the Institute for Genomic Biology at the University of Illinois, where Dr. Woese worked for many years.

For years, science confidently divided the vast tree of life into two great domains: microbes of all sorts and the more complex animals that populate the visible world.

Carl Woese holds a model of ribonucleic acid chain at the General Electric research lab in Schenectady, N.Y. (1961 FILE PHOTO /Associated Press)

A microbiologist, Dr. Woese “wanted to have a way of classifying microbes,” Robinson said. But he found that, even by viewing the microbes through microscopes, the observable physical characteristics did not provide Dr. Woese with “enough good diagnostic information.”

His response, Robinson said, was to search beyond the physical qualities of microbes to examine their molecular structures. Dr. Woese’s biological breakthrough came through the study of genes, which determine heredity and govern the development of living things. By focusing on the genetic molecules known as ribosomal RNA, Dr. Woese developed a new way of classifying species, which led to the identification of a third domain of life, known as the Archaea. Judged by the findings of gene sequencing, the Archaea are considered as different from bacteria as bacteria are from bull elephants.

Previously, scientists believed that single-celled Archaea inhabited only extreme environments, but they have been found in more benign locales, including the human navel.

Dr. Woese’s groundbreaking paper appeared more than 35 years ago, and acceptance of his views was not instantaneous. Important figures in biology expressed skepticism about the way he seemed to split the microbial domain. In acknowledgment of the vigor of the debate, a scientific journal once depicted him as “Microbiology’s Scarred Revolutionary.”

But the accretion of data appeared to overwhelm objections. In time, according to Dr. Woese’s admirers, biology textbooks routinely embraced all three domains of the tree of life.

Colleagues described a researcher devoted to transmitting knowledge and pursuing science for its own sake. They depicted him as an admirer of jazz and poetry who was frequently seen in khakis, plaid shirts and sneakers.

Carl Richard Woese was born July 15, 1928, in Syracuse, N.Y. He attended the private Deerfield Academy in Massachusetts and received a bachelor’s degree from Amherst College in Massachusetts in 1950. He received a doctorate in biophysics from Yale University in 1953 and completed two years of medical school at the University of Rochester in New York.

After postdoctoral research at Yale University, and several years of working for General Electric in Schenectady, N.Y., Dr. Woese went to Illinois in 1964.

Regarded as a prophet in science, Dr. Woese was not without honors. He received the National Medal of Science in 2000 and was a member of the National Academy of Sciences. In 1992, he was awarded the Leeuwenhoek Medal, presented once every decade by the Dutch Royal Academy of Science and often called the highest honor in microbiology. In 1984, he received a MacArthur fellowship, commonly known as a “genius grant.”

Survivors include his wife, Gabriella Woese, two children and a sister.