The oldest things on campus


The author holding one of the Allende meteorite specimens from the Kentucky Geological Survey collection.

Kent Ratajeski, Reporter

What is the oldest thing on campus?

Strap in for a tour of campus and into the deepest recesses of geologic time.

Perhaps one’s first guess is that the oldest thing on campus would be its oldest building. That honor goes to the Main Building, the current home of the UK administration. It was built in 1882, back when UK was called the State College of Kentucky.

Buildings are constructed from materials which are far older than the buildings themselves. The gray and white limestones near the base of the Main Building were quarried locally from two bedrock formations, the Lexington and Tyrone Limestones. Frank Ettensohn, a professor in the Department of Earth and Environmental Sciences knows how old they are.

“There are layers of shale within these formations called bentonites which were formerly volcanic ashes,” Ettensohn said. “Some of the minerals in those ashes, like zircon, can be dated radiometrically.”

So how old are those rocks in the Main Building? Back when the Tyrone Limestone was being deposited 454 million years ago, Kentucky was covered by a shallow, tropical sea teeming with ancient life on a different continent located in the southern hemisphere.

The Kentucky Geological Survey (KGS) is a state agency located at UK that stores thousands of drill cores obtained from all over the state in their Earth Analysis Research Library near the Kentucky Horse Park. A few of those wells were drilled thousands of feet down, deep enough to reach and sample the ancient crystalline rocks which are buried beneath younger sedimentary layers.

A pink granite from the bottom of a deep core from Bourbon County is displayed on the third floor of the Mining and Mineral Resources Building at the KGS headquarters on Rose Street. David Moecher, a professor at UK’s Department of Earth and Environmental Sciences, dated this rock using isotopes of uranium and lead locked inside tiny crystals of zircon within the rock.

“The granite underlying central Kentucky was hypothesized to have an age of 1.45 billion years,” Moecher said. “However, as often happens in earth science, we are surprised to find the story is more complicated. The Bourbon County granite is only 1.33 billion years old.”

If that age isn’t impressive enough, Moecher has collected and studied ancient rocks from eras of Earth geologic history far predating those found under Kentucky. Moecher said his best guess for the oldest Earth rock on campus is a striped, reddish metamorphic rock called the Montevideo Gneiss that he collected in southwestern Minnesota.

“The Montevideo Gneiss is one of several rocks in the central US that was involved in a worldwide competition to find the oldest rocks,“ Moecher said. “Because the rock has such a complex history, it wasn’t until 2013 that highly reliable results were obtained that prove it is 3.5 billion years old.”

That’s about three-quarters of the Earth’s known age.

The oldest rocks on campus are not from Earth, however, and a bunch of them are on display in the lobby of the Mining and Mineral Resources Building. The Kentucky Geological Survey’s meteorite collection is curated by Ethan Davis.

“We have over 200 specimens … from every continent,” Davis said. “The large majority of our meteorite collection resulted from the generous donations from two private collectors, Mary Ann Russell and William Ehmann. Ehmann was a UK chemistry professor and NASA researcher who was one of the first scientists to analyze moon samples from the Apollo missions.”

Some meteorites were formed by geologic processes in the crusts, mantles and cores of asteroids and planetary bodies early in the history of the solar system. Other meteorites represent more primitive materials that gravitationally coalesced to form smaller bodies: these were likely the original starting materials from which larger asteroids and planets were constructed. Meteorites of this latter group, called chondrites, are thought to have formed within the original solar nebula which gave birth to our solar system about 4.5 billion years ago.

The KGS collection includes two of the most famous chondrites to visit Earth: the Allende and Murchison meteorites, both of which arrived as showers of stones in separate falls in 1969 in Mexico and Australia, respectively.

Both are black in color because they contain significant amounts of carbon; they are examples of a class of meteorites called carbonaceous chondrites. Significantly, both meteorites also contain amino acids, the building blocks of organic life.

The Allende and Murchison meteorites contain three types of objects of interest for our search for the oldest things on campus. Both are chondrites, and are therefore dominated by chondrules, small spherical objects made of common silicate minerals.

The textures of chondrules suggest that they formed from droplets of magma floating in space. Theories of their origin vary widely, but most experts agree that chondrules are among the oldest things in our solar system.

Even older than chondrules, small irregularly-shaped aggregates of whitish minerals called calcium-aluminum inclusions, or CAIs, are also present in the Allende and Murchison meteorites.

“CAIs are believed to contain the first solid objects to form in the cooling solar nebula at the birth of our solar system … over 4.5 billion years ago,” Davis said. “I find it awe-inspiring to look at Allende and know that parts of this meteorite formed at the dawn of our solar system, millions of years before planet Earth.”

Objects even predating the solar system itself have been found in the Allende and Murchison meteorites.

Invisible to the naked eye, presolar grains are sub-microscopic, nano-scale aggregates and crystals of carbon-rich minerals (graphite, diamond, and silicon carbide). They are usually obtained for study by crushing and dissolving whole meteorite samples in strong acids.

Presolar grains are believed to originate from stars other than our sun which exploded long ago in supernova explosions, scattering their debris throughout the cosmos. Some of this debris was eventually incorporated within the seeds of our forming solar system.

Scientists theorize that shock waves from these supernova explosions may actually have triggered the formation of the solar system itself.

Using isotopic methods based on exposure to cosmic rays during their time in space, researchers have estimated ages ranging from 4.6 to 7 billion years for presolar grains from the Murchison meteorite. The oldest objects on this campus predate the Earth and even the Sun itself.

Walking along Rose Street? Stop in and visit the oldest things on campus!