Kirk Johnson, PhD

  • POSITIONVice President of Research & Collections and Chief Curator
  • EXPERTISE Fossil plants and geology
  • PhD

    Yale University

  • PHONE NUMBER303.370.6448
  • EMAIL[email protected]
  • RESUME Click to download
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Dr. Kirk Johnson studies fossil leaves and measures the age of the rocks he finds them in. This allows him to refine geologic time, reconstruct ancient landscapes, track climate change, and document the evolution and extinction of species and ecosystems.


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The Snowmastodon Project™

On October 14, 2010, bulldozer operator Jesse Steele was excavating a reservoir near Snowmass Village when he saw bones coming over the top of his bulldozer blade. Within two days, scientists from the Denver Museum of Nature & Science were on site, and within two weeks a Museum team was excavating what has become one of the most significant scientific discoveries in Colorado history.

The find is an exceptionally preserved Ice Age ecosystem. As of December 2010, the site had produced the remains of eight to 10 American mastodons, four Columbian mammoths, a Jefferson's ground sloth, four gigantic bison, two Ice Age deer, snails, iridescent insects, and plant matter that is still green after more than 45,000 years.

News of the once-in-a-lifetime discovery spread like wildfire throughout Colorado, generating enormous public interest. In the Roaring Fork Valley, 8,500 school children lined up to see the bones and learn about the discovery from Museum educators. During two days in November, more than 3,500 people in Snowmass Village and 2,500 people in Denver attended Mammoth and Mastodon Madness Days to see the fossils and learn more about the Ice Age in Colorado.

For the next six months, the Museum is focusing on preserving the bones from this Ice Age treasure trove and planning next steps. Museum scientists have assembled a team of more than two dozen scientific experts who will gather in Snowmass Village in May 2011 to continue this amazing excavation.

Get Involved

Click here to get caught up on everything that happened in the field, learn what scientists are doing now to preserve the bones, and find out the latest discoveries from our team of experts.

Denver Basin Project

The Denver Basin is a bowl-like geologic structure that underlies the area between Boulder, Colorado Springs, and Limon. The bedrock and sediments below the surface hold amazing plant and animal fossils that lived at the end of the Cretaceous between 69 and 34 million years ago. The rocks that span this time period are up to 3,000 feet thick and are exposed in road cuts, parks, gullies, and construction sites all along the Front Range. In 2003, a volunteer from the Denver Museum of Nature & Science discovered a six-foot-long skull of a Triceratops dinosaur at a housing development in Brighton.

The Museum's Dr. Kirk Johnson oversees the ongoing Denver Basin Project to study the rocks, fossils, and groundwater in the basin, along with Dr. Ian Miller and research associate Dr. Bob Raynolds.

Dr. Johnson's research focuses mainly on fossil plants. In 1994 when Steve Wallace, a paleontologist with the Colorado Department of Transportation (CDOT), discovered a 64 million-year-old tropical rain forest along Interstate 25 in Castle Rock, Dr. Johnson was ecstatic. He calls it one of the Museum's most significant finds.

"The Denver Basin contains tons of fossil leaves and pollen from just the time period I like.  My specialty time period is between 60 and 70 million years ago, and the sediments in the basin fall right in this time range. I didn't even realize this when I moved to Denver, and then I got here and found that there were fossils everywhere," Dr. Johnson said.

Many of the fossil leaves from Castle Rock are large, with smooth margins and drip tips. After studying these leaves and their similarities to modern rain forests, Dr. Johnson concluded that Castle Rock once had more than 80 inches of rainfall and an average annual temperature warmer than Miami. Essentially, the place where Castle Rock now stands used to be a tropical rain forest.

Finds like these continue to happen in the Denver Basin, which is why Dr. Johnson calls it "the no-brainer project." The National Science Foundation funded this work from 1998 to 2008, but the Museum continues to interact with CDOT, regional parks, and private landowners to salvage fossils from natural outcrops and  construction sites as they are discovered.

Kaiparowits Basin Project

The Kaiparowits Basin Project focuses on the Grand Staircase-Escalante National Monument (GSENM) in southern Utah, led by Dr. Scott Sampson of the University of Utah. GSENM is located in an extremely remote and wild area and was one of the last regions in the lower 48 states to be explored. This amazingly beautiful area is full of fossil plants and animals between 95 and 74 million years old and is arguably one of the last unexplored dinosaur bone yards in the United States.

The dinosaur species being discovered are new to science. Many of them are so well preserved that impressions of their skin are common.

Relying on other branches of geology and paleontology, the Kaiparowits Basin Project looks to understand the ancient environments in which the dinosaurs lived. This includes studying fossil plants. Dr. Kirk Johnson and Dr. Ian Miller of the Denver Museum of Nature & Science are doing this basic paleobotanical exploration and excavation.

"It's huge, big country that's really hard to work in. The fossils plants are difficult to find, but when you do find them, they are gorgeous," said Dr. Johnson.

The story emerging from these fossil discoveries shows a diversity of life that lived in a swampy, subtropical coastal plain overrun by flowering plants. As research and fieldwork continues, more elements of this ancient narrative will come to light.

"Think about fossil leaves as trading cards. It's possible to collect hundreds and hundreds of them, and with this sort of sample size you can begin to rebuild lost ecosystems," Dr. Johnson said.

This project is supported by the National Science Foundation, the KT Challenge Fund, the Bureau of Land Management, and the Denver Museum of Nature & Science.

Patagonia Paleobotany

As they hike the badlands and valleys of windswept Patagonia, Dr. Kirk Johnson, of the Denver Museum of Nature & Science, and a team of scientists from Argentina and Pennsylvania State University search for fossils. They have found sites in Chubut, a province in the southern part of Argentina, ranging from 68 to 47 million years old.

"Very little work has ever been done here, so what we're doing is pioneering," said Dr. Johnson.

What the team hopes to understand is the origin of South American vegetation, and to document its relationship to the fossil vegetation of Antarctica, as well as the fossil and living vegetation of Australia and New Zealand. Recently, they discovered the first examples of non-Australian Eucalyptus.

"There are 700 hundred kinds of Eucalyptus in Australia, and it's found nowhere else in the world.  But in Patagonia we're finding fossils of it that are older than the fossils in Australia," said Dr. Johnson. And it's not just Eucalyptus they are finding. Dr. Johnson and his team have found a variety of plants that in today's world exist only in the mountains of Australia and New Guinea. His colleagues at the Egidio Feruglio Paleontology Museum in the town of Trelew even found fossils of a South American platypus.

Dr. Johnson said that this tells him that Antarctica once served as a bridge between Australia and South America. Fifty million years ago when the world was warm and ice-free, this whole area was one continuous forest.

"Surprisingly, the fossil plants we are finding in central Patagonia have more to do with the forests of Australia than they do with the forests of the Amazon," said Dr. Johnson. The National Science Foundation will support this project through 2014.

Maastrichtian-Paleocene Geochronology

How do you measure time? You can measure seconds, minutes, and hours with a clock, but how do you measure really big time, such as millions and billions of years?

Dr. Kirk Johnson of the Denver Museum of Nature & Science is using zircon crystals that erupted from volcanoes. He is collaborating with geochronologist Dr. Sam Bowring of MIT and magnetostratigrapher Dr. Will Clyde from the University of New Hampshire. Together they are dating volcanic ash beds from the Rocky Mountain Region that are between 70 and 55 million years old, geologic time units known as the Maastrichtian and the Paleocene.

"The study of Earth history is only as good as the resolution of rock-dating methods. Our efforts are greatly enhancing our ability to study extinction, evolution, and climate change in the distant past," Dr. Johnson said. 

But how can studying zircon help us understand time? Its combination of stability and instability makes it the perfect big-time problem solver. Zircon is dense, inert, and nonmagnetic. It also resists weathering, withstands temperature extremes, and strongly rejects lead when it forms. In these ways, zircon is incredibly stable. Within this tough crystal, however, there is a useful instability. Zircon contains radioactive uranium. From the moment a zircon crystal forms, unstable uranium begins to decay into stable lead. Over time, the amount of uranium decreases and the amount of lead increases. 

When scientists study a zircon crystal and measure the ratio of uranium to lead, it's like a very precise stopwatch, one that dates events from a few hundred thousand years ago to several billion years ago.

"Our methods allow for amazing precision. We have been able to date the K-T boundary extinction to a precision of plus or minus 12,000 years, where previous workers achieved plus or minus 300,000 years," Dr. Johnson said. 

This project is funded by the National Science Foundation through 2011.


Dinosaurs on the Colorado River

Take a journey along the Colorado River and back to the time of the dinosaurs. This family friendly trip will travel 140 to 90 million years into the past and explore the formations of the Jurassic and Cretaceous Periods.

Nature Walks New!

Ages 4 & 5

See what's living in City Park.

Digging Snowmastodon

If you couldn't get your hands dirty at the historic dig near Snowmass Village, then get your hands on a copy of the book that tells the story.  Help us celebrate the book launch of Digging Snowmastodon: Discovering an Ice Age World in the Colorado Rockies, bring your questions, and hear about "hot off the press" Snowmastodon research.

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