Geology 12 – Dalesandro
Assignment 12 – Ice Ages, Extinctions, & Climate Change
Instructions: Sit with a partner. Read the articles “Ice Age Ends Smashingly” and “Comet
Impact”. Answer the questions below in full sentences. Pass in your completed questions
(one copy per group).
Due: One week from today.
Value: 20 points.
Questions:
Article #1 – “Ice Age Ends Smashingly”
1) What is the main idea of the new theory put forward to explain the end of the last ice age?
2) What effects did this supposed event have on the environment at the time?
3) List two pieces of evidence seeming to support this new theory.
4) What fact leads scientists to believe that the object was a comet, not an asteroid?
5) How would this event have contributed to global cooling, despite the global warming which
was occurring at the time?
6) What does your group think of this new theory after reading article #1? Explain your
thinking in a well-written paragraph (5 sentences).
Article #2 – “Comet Impact”
1) What are some of the effects Richard Firestone says would have accompanied a comet
exploding?
2) List some of the major species of animals that disappeared 12 900 years ago in
North America?
3) What other theory could explain the extinction of these animals?
4) What type of early human civilization also disappeared with the animals? Why does its
disappearance support the comet theory?
5) What were the new human civilizations like, once they had recovered from the comet
disaster?
6) What is the Younger Dryas period? What happened during this period? Why does it support
the comet impact theory?
7) What do you think of the comet impact theory after reading article #2? Has your opinion
changed at all? Why or why not?
Ice Age Ends Smashingly: Did a comet blow up over eastern
Canada?
By Sid Perkins
Evidence unearthed at more than two dozen sites across North America suggests that an
extraterrestrial object exploded in Earth's atmosphere above Canada about 12 900 years
ago, just as the climate was warming at the end of the last ice age. The explosion
sparked immense wildfires, devastated North America's ecosystems and prehistoric
cultures, and triggered a new “mini-ice age” which lasted for a thousand years, scientists
say.
The layer of carbon-rich sediment (arrow) found here at Murray Springs, Ariz., and elsewhere
across North America, provides evidence that an extraterrestrial object blew up over Canada
12,900 years ago. The effects of the comet’s destruction include lumps of glasslike carbon (top),
carbon spherules (middle, in cross section), and magnetic grains rich in iridium (bottom).
At sites stretching from California to the Carolinas and as far north as Alberta and
Saskatchewan—many of which were home to the prehistoric Clovis people—researchers
have long noted an odd layer of carbon-rich sediment that was laid down nearly 13 000
years ago. "Clovis artifacts are never found above this black layer of material," says Allen
West, a geophysicist with Geoscience Consulting in Dewey, Ariz. The layer, typically a
few millimeters thick, lies between older, underlying strata that are chock-full of
mammoth bones and younger, fossil free sediments immediately above, he notes. Did
the exploding object exterminate both the Clovis and the mammoths?
New analyses of samples taken from 26 of those sites reveal several hallmarks of an
extraterrestrial object's impact, West and his colleagues reported at the spring meeting
of the American Geophysical Union in Acapulco, Mexico. Samples from the base of the
black mat yield most of the clues to its extraterrestrial origin, says Richard B. Firestone,
West's coworker and a nuclear physicist at the Lawrence Berkeley (Calif.) National
Laboratory. Some of the particles there are small, magnetic grains of material with
higher proportions of the element iridium than are typically found in the Earth's crust, he
notes.
Also in the odd layer are tiny lumps of glasslike carbon that probably formed from molten
droplets of the element. These lumps even contain tiny diamonds formed under intense
pressure and heat – the same levels of pressure and heat an impact would bring.
A host of unusual geological features, collectively known as the Carolina Formation, hints
at the cataclysm's location, says team member George A. Howard, a wetland manager at
Restoration Systems, an environmental-restoration firm in Raleigh, N.C. Around 1 million
elliptical, sand-rimmed depressions, measuring between 50 meters and 11 kilometers
across, scar the landscape from New Jersey to Florida. In samples taken from 15 of the
features, Howard and his colleagues found iridium-rich magnetic grains and carbon
spherules with tiny diamond fragments similar to those found at Clovis archaeological
sites.
The Carolina Formation points toward locations near the Great Lakes and in Canada—a
hint that the extraterrestrial object disintegrated over those locales, says Howard.
Because scientists "haven't discovered a large, smoking hole" left by the event, the
object that blew up in the atmosphere probably was a comet, says West, not an asteroid.
Asteroids hold together better as they pass through our atmosphere and leave behind
larger, easier-to-find craters.
Whatever the nature of the object, heat from its disintegration would have set off
wildfires across the continent, the scientists suggest. The shock from the explosion
probably broke up portions of the ice sheet smothering eastern Canada at the time, they
add. The flood of fresh water into the North Atlantic that resulted would have interrupted
ocean currents that bring warmth to the region, and thick clouds of smoke and soot in
the air would have intensified cooling across the Northern Hemisphere. The estimated
date for the event matches the beginning of a 1 200-year-long cold spell that geologists
call the Younger Dryas, which in its first few decades saw temperatures in the Northern
Hemisphere drop as much as 10°C.
Comet Impact May Have Led to Mammoths' Extinction
Wooly mammoths once roamed North America. Did a comet kill them?
By Sean McDermott
There's a new extraterrestrial suspect in the mysterious, highly debated disappearance of
the woolly mammoth some 12 900 years ago. A team of two dozen scientists say the
culprit was likely a comet that exploded in the atmosphere above North America.
The explosions sent a heat and shock wave across the continent, pelted the ground with
a layer of telltale debris, ignited massive wildfires, and triggered a major cooling of the
climate said nuclear analytic chemist Richard Firestone of Lawrence Berkeley Laboratory.
He is one of the scientists that presented the controversial new theory Thursday at a
conference of the American Geophysical Union in Acapulco.
At least 15 species, mostly large mammals including mammoths, mastodons, giant
ground sloths, camels and horses, were wiped out around the same time. Firestone and
his colleagues believe some may have been killed by the explosions, and the rest died off
after fires burned the vegetation they depended on.
"It seems awfully coincidental that the mammoths died at exactly the same moment
where we find this impact layer," said Allen West, a member of the team from GeoScience
consulting in Dewey, Arizona. The scientists are bracing themselves for fiery reaction to
their theory.
The extinctions were already a hotly debated event with scientists split between two
theories. The leading theory is that humans hunted the animals into extinction soon after
arriving in North America. Some scientists also blame climate change as the earth
warmed up after the last ice age. Still others think it was more of a one-two punch with
climate change weakening the animal populations and human hunters delivering the final
blow.
But the impact theory is gaining popularity. “It has the advantage of explaining why the
Clovis ‘cave people’ disappeared along with the mammoths”, says archeologist Douglas
Kennett of the University of Oregon. “For 300 years, Clovis people hunted mammoths and
other animals with distinctive spear heads with fluted ends known as Clovis points. Then,
suddenly, they vanished along with their prey.”
The team visited archaeological sites containing Clovis points across North America and
collected samples of the sediment that covered the last signs of Clovis people and the last
mammoth bones.
They found many distinctive signs of an extraterrestrial impact including rounded
magnetic grains that formed when pieces of the comet were thrown back into space after
the explosion and then melted into round grains as they re-entered the atmosphere.
They also found high levels of iridium and a special form of carbon molecules known as
fullerenes that have helium atoms trapped inside, and microscopic diamonds called
nanodiamonds. They also found strange rounded carbon grains and glass-like carbon that
looks like hardened black taffy. Lots of soot and charcoal are evidence of the ensuing
wildfires
"We really have found the mother lode of impact material," Firestone said.
Above this layer of strange sediment there are no signs of mammoths or many of the
other large mammal species of the day, or of the distinctive Clovis points. At many of the
sites there is a gap in evidence of humans for several hundred years before new types of
spearheads show up.
Just like the mammoths, many of the Clovis people could have been killed by the comet.
The survivors would have struggled to survive once many of the animals they hunted
died. The remaining people may have delivered the final blow to the last of the large
mammals. These people made it through, and slowly the human population rebounded.
Post-Clovis people were more culturally diverse, as reflected by an array of different
spearheads, said Kennett. "This may suggest the survivors could have been separated
into smaller groups across the continent that developed differing cultural traditions and
spearhead designs".
The comet’s explosion may also be the key to an enigmatic episode of cooler climate,
known as the Younger Dryas period, that began around the same time and lasted about 1
200 years. The earth had been steadily warming up after the last ice age due to cyclical
changes in the planet's orbit that brought it slightly closer to the sun. Then suddenly, the
climate started cooling for no obvious reason at a time when it should have still been
warming up.
"Earth was warming and then suddenly went back to cooling for a thousand years,"
Firestone says. "That’s odd."
The new comet theory will undoubtedly come under fire from several directions, including
some scientists who say climate change, not a comet impact, caused the animal
extinctions.