[meteorite-list] Clues to Dinosaur Extinction May Lie Buried in Colorado

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Sep 13 12:48:59 2005
Message-ID: <200509131647.j8DGlmu00785_at_zagami.jpl.nasa.gov>

http://www.gazettetimes.com/articles/2005/09/13/news/the_west/tuewst01.txt

Clues to dinosaur extinction may lie buried in Colorado
By BILL VOGRIN
Corvallis Gazette-Times
September 12, 2005

COLORADO SPRINGS, Colo. - Kirk Johnson swung his pickax against the base
of Pulpit Rock and broke off a football-sized chunk resembling a piece
of cake thinly layered with light and dark chocolate.

A gentle whack against its side split it open to reveal a perfectly
preserved, three-pointed, prehistoric tree leaf the size of a man's hand.

"Look at this,'' Johnson said excitedly to project manager Beth Ellis
and geologist Bob Raynolds, his team of fossil prospectors from the
Denver Museum of Nature & Science. "This is a really nice one; maybe the
best we've found yet.''

During a three-day dig, the team gathered dozens of similar fossils from
Pulpit Rock and at an outcropping along nearby Rusina Road. The two
sites are among many in the area that Johnson, chief curator of
paleontology at the museum, and other scientists visit in their quest to
reconstruct life through the ages.

"Colorado Springs is one of the best places in the world to see the
history of the Earth,'' Johnson said, because of its exposed or easily
excavated prehistoric molten rock and caches of volcanic ash, mud and sand.

He started studying the rock under Colorado Springs in 1991 and
intensified efforts in recent years because of the wealth of fossils and
the access to many layers of rock offered by the region's topography.

"We are trying to build the geology of the Rocky Mountains as of 65
million years ago,'' Johnson said. "We are trying to understand how the
landscape changed and reconstruct the Rocky Mountains.''

Eventually, Johnson and his team will publish their findings in news
articles and scientific journals, use results of their research to
update museum exhibits and include it in future lectures. But that will
take a while.

"We take a bag of leaves and can tell what the forest looked like,''
Johnson said. "We'll dig up 400 or 500 leaves and study them.''

The leaves gathered last week will help him determine whether the
landscape was arid or a rainforest or made up of conifers and pine trees
- at least, ancient predecessors of today's tree species.

"We're looking here at a whole suite of leaves that are previously
undiscovered and undescribed,'' Johnson said. "We've found a couple
kinds of conifers and a couple of ferns and broadleafs. But exactly what
they are, we don't know.''

The one thing he is sure of is that the leaves were between 65.5 million
and 68 million years old.

Johnson thinks the latest leaf lived on a tree during the Cretaceous
period - a time when the 5-ton Tyrannosaurus rex lumbered to the top of
the food chain and the lush forest also was home to the plant-eating
Triceratops, as well as other dinosaurs, birds, mammals and other organisms.

The evidence is buried within Pulpit Rock, a spired outcropping of
white, layered sandstone that rises near Interstate 25.

More than just a striking landmark, Pulpit Rock has survived 10 million
years of erosion by Monument Creek - erosion that also unearthed and
created the world-famous rock formations in Garden of the Gods, the
hogbacks of Red Rock Canyon and hoodoos throughout the area.

Pulpit Rock is a vault, of sorts, where Mother Nature stored fossil
clues - like the leaves, as well as dinosaur bones, volcanic ash pits
and even grains of pollen - for scientists like Johnson to use.

In most places on Earth, these vaults remain deep underground. They are
accessible around the Springs because of a dramatic uplift about 68
million years ago that created Pikes Peak and the Front Range.

The uplift was so powerful that it thrust up tons of granite to create
the 14,115-foot mountain. Elsewhere, you have to dig 14,000 feet below
the surface to find Pikes Peak-type granite.

The uplift also bent and pushed to the surface layers of rock formations
that define each era spanning 500 million years. Those layers have been
exposed by erosion from wind and water, and scientists now mine them for
clues to the past.

Perhaps the most important clue is a centimeter-thick layer of clay,
laced with unique space dust called iridium.

Scientists generally believe an asteroid the size of the Air Force
Academy smashed into Mexico's Yucatan Peninsula - a violent collision
that incinerated the atmosphere and caused an eruption of ash that
blanketed the globe, wiping out most plant and animal life on Earth,
including the dinosaurs.

The ash - with its space dust, crystals and soot from global fires -
eventually compressed into the layer of clay that lies buried beneath
65.5 million years of sedimentary rock.

It separates two distinct periods of time on Earth - the Cretaceous,
when dinosaurs lived and became extinct, and the Tertiary, which gave
rise to the age of mammals.

The thin layer of clay is known as the K/T boundary (K for the German
spelling of Cretaceous and T for Tertiary) and some think it runs
throughout Colorado Springs.

"The boundary is so important because it is a precise marker in geologic
time,'' Johnson said.

So prospecting above and below the boundary allows scientists to more
accurately date their fossils and reconstruct life.

It's not a high-tech exercise. The leaves collected in the sun and heat
were wrapped in toilet paper, placed in cardboard boxes and taken back
to the museum for study.
Received on Tue 13 Sep 2005 12:47:48 PM PDT