The Asteroid that Killed the Dinosaurs
Word Count: 1862
Introduction
Complex formulas, technical jargon and abstract theories are all commonplace in
scientific writing. Although these writings are often too complex for the general public,
the concepts that they present can still be of general interest. The burden of converting
these scientific reports into clear, concise, and entertaining pieces of literature lies with
journalists. Those who write for the Science, Technology, or Health sections of
newspapers must be able to transform writings from the scientific realm into a more
reader-friendly version while ensuring the core concepts remain sound. Far-flung
asteroid crash doomed the dinosaurs is one such article (See Appendix A). Written by
Matthew Trevisan and appearing in the Globe and Mail on September 6, 2007, this
article summarizes the findings of Dr. William Bottke, Dr. David Vokrouhlikcy, and their
colleagues about the origin of the asteroid that is believed to have killed the dinosaurs.
Trevisan chose a topic that many people are aware of, the death of the dinosaurs. He
was then able to present recent scientific findings in a casual, yet informative piece of
writing. The first section of this paper will explore the science behind this article by
reviewing other works in the field in order to gain a broader understanding. The second
section will analyze the writing of Matthew Trevisan detailing the choices he made and
the style of his work.
The Science Behind the Article
Matthew Trevisan’s article contains numerous references to scientific concepts
and papers; it is obvious that he did extensive research on the subject before writing his
article. This section will expand on the concepts that were introduced in the Far-flung
asteroid crash doomed the dinosaurs article to gain a broader understanding of the
science behind the article. The section will be divided into three subsections starting
with the collision that created the asteroid, the mechanisms for its movement across the
solar system and the discovery of its crater.
The Collision
Trevisan’s article is based on a paper by William F. Bottke, David Vokrouhlicky
and David Nesvorny, who conducted research on a collision of two large asteroids in
the asteroid belt which may have led to the extinction of the dinosaurs (Bottke et al.
2007). The collisions of major asteroids led to the creation of many smaller fragments of
the original two asteroids; collectively, these pieces are classified as a family. Bottke
and his colleagues (2007) theorize that between 160-190 million years ago (Ma) a
collision between a 170 km wide and a 60 km wide asteroid occurred in the asteroid belt
located between Mars and Jupiter. The asteroids that resulted from this collision are
classified as members of the Baptistina Asteroid Family (BAF) (Bottke et al. 2007).
Research carried out by Menichella and colleagues (1995) determined that, on average,
only about one hundred 1 km-sized asteroids are created per year and asteroids larger
than 10 km are very rare. These numbers could be increased by a factor of 1000 in the
event of a large scale collision like one suggested by Bottke. Bottke and his colleagues
(2007) propose that the collision that created the BAF produced approximately 300
asteroids greater than 10 km wide and just under 140 000 over 1 km wide.
Bottke and his colleagues (2007) came to these conclusions by observing that
over the past 100 million years there has been a substantial increase in the rates of
meteors colliding with planets; they inferred that these impacts were probably the result
of the creation of another asteroid family. After the creation of an asteroid family, the
members are affected by the Yarkvosky effect, the YORP effect and numerous other
astrophysical phenomena; these effects combine to leave a distinctive mark on all
asteroids of a family. Bottke and his colleagues (2007) used these distinctive traits to
classify all the members of the BAF and, by the size and distribution of the BAF, Bottke
concluded that one parent asteroid was 170 km wide while the other was 60 km wide.
The Mechanism of Movement
After the collision, the asteroid needed some mechanism to propel it towards
Earth; the authors of the paper suggest the Yarkovsky Effect. The Yarkovsky Effect was
named after Ivan Yarkvosky who theorized that an object in space would absorb heat
from the sun and, when it radiated the heat, the object would experience a force (Bottke
2006). The idea is based on the anisotropic nature of the object. Anisotropic refers to
the differing properties of a material depending on direction and these differences will
cause it to radiate the energy that it absorbed from the sun at different rates depending
where on the object the energy is being emitted (Broź 2006). These different rates of
emission will cause a force which, in turn, will cause the object to move. Bottke and his
colleagues (2007) theorize that after the creation of the BAF, an asteroid of
approximately 10 km began to experience a Yarkovsky Effect and started moving
towards Earth. This idea that the Yarkovsky Effect could propel an asteroid is supported
by earlier work on the Koronis Asteroid Family carried out by Bottke and his colleagues
(2001). This BAF asteroid continued to be propelled by the Yarkovsky Effect until it
reached a resonance and was carried towards Earth (Bottke 2007).
The Crater
If Bottke’s theory is correct that the asteroid from the BAF was responsible for the
impact that killed the dinosaurs, then evidence of the impact crater must exist on earth.
The death of the dinosours defines the Cretaceous/Tertiary Boundary (K/T Boundary)
and is dated at 65Ma (Russel 1979). The first evidence of this crater was discovered by
Alvarez and his colleagues (1980) who discovered a layer of rock dated at 65Ma that
was present in many locations across the Earth. This rock had at least twenty times the
normal iridium content and contained tektites and shocked quartz, characteristics that
are indicative of a major asteroid impact.
The findings of Alvarez and his colleagues were not widely accepted by the
scientific community because no one could imagine that such a large impact could have
occurred with no resulting crater appearing to exist (Hildebrand, 1991). This skepticism
remained until the likely crater was later discovered by Dr. Hildebrand in 1991 on the
Yucatan Peninsula which is located just off the coast of Mexico. Named the Chicxulub
Crater, this crater is approximately 180 km in diameter and is determined to have been
formed by an impact at the K/T boundary, 65Ma ago (Hildebrand, 1991). This impact
crater provides one of the final pieces of evidence needed to support the theory
proposed by Bottke and his colleagues.
To further support the authors’ findings, additional research must be conducted; if the
asteroid that destroyed the dinosaurs was part of the larger BAF, then additional craters
from BAF-member impacts must exist. Bottke and his colleagues (2007), identified
potential craters caused by BAF members, such as Tycho, a large crater on the moon.
The Tycho Crater is believed to have been created around 95±6 Ma, which is
considered to be within the reasonable timeframe for it to have been created by a
member of the BAF (Arvidson 1976). If the Tycho crater is found to be the result of a
BAF-member impact, Bottke and his colleagues’ findings will be further strengthened.
Writing Style
Attention
An important part of a newspaper article is its title, as it has to compete with a
wide variety of distractions; it needs to intrigue the reader perhaps by being of interest
to the reader or by having an outlandish statement that piques the reader's curiosity.
The article I chose is the former; it is about dinosaurs, something that interests me. I
think many children, including myself, at one time or another were utterly fascinated by
dinosaurs. Although dinosaurs were the dominate species on our planet for thousands
of years, nothing remains of these creatures today except some fossilized bones and a
footprint here or there. By choosing to write on the topic of dinosaurs, Trevisan
immediately tapped into a large audience of interested readers.
This article held my attention, mainly because it is well written and is able to
explain a rather complex theory effectively and concisely. Trevisan uses a mixture of
less formal writing, using words such as “smashed” and “smacking” and catchy sections
titles such as “The big crunch” together with some complex ideas such as the
“Yarkovsky effect’ or “resonances” (Trevisan 2007).
He also includes the input of
numerous individuals in the field from a wide variety of institutions, such as Dr. Philip
Stooke from University of Western Ontario or Dr. Martin Duncan from Queen’s
University to add additional credibility to his work (Trevisan 2007).
Why I was interested in the science
Like many others, I was, at one point, enthralled with dinosaurs. I wanted to know
all about them, how big they were, what they ate, what color they were. But most of all I
wanted to know where they went. I have been able to hear Dr. Hildebrand, the
discoverer of the impact crater, lecture on how he found the crater. To then be able to
read about how a collision between a 170 km wide asteroid and a 60 km wide one some
200 million km away from Earth somehow managed to destroy over half the life on
Earth was of great interest to me (Trevisan 2007). The odds that one of the fragments
from this collision would collide with the Earth piqued my curiosity. I was particularly
intrigued when Trevisan (2007) detailed how a 10 km wide asteroid was moved by
sunlight. By choosing to write on a well-known topic and by including some thought
provoking facts and figures, Matthew Trevisan was able to a write an article that
attracted and held my attention.
Conclusion
By reviewing the scientific literature, it becomes evident that the claims made by
Bottke and his colleagues are not only reasonable, but are also well-supported by preexisting research in the field. Additional research, however, is needed on the topic to
provide more examples of BAF-member impacts, which would help to further strengthen
the claims made in the Bottke paper.
It is clear that Trevisan did an excellent job of converting a complex and theoryfilled paper by Dr. Bottke and his colleagues into a well written, entertaining article.
Trevisan’s article grabbed attention by having a title that included well-known subject
matter, and it was able to hold the attention by being written with a pleasant mixture of
science and casual commentary in an entertaining manner. By including concrete
details in his article, Trevisan was able to make the concepts easier to understand.
Also, when Trevisan added the remarks of several expert sources, he was able to
instantly add credibility to the article.
By reviewing the science behind the article written by Matthew Trevisan, it is
evident that his work Far-flung asteroid crash doomed the dinosaurs was effectively
able to convey the points of the paper by Bottke and his colleagues. Matthew Trevisan
was able to take a very technical piece of writing and, by summarizing the major points
and supplementing it with additional facts and commentary from experts in the field,
create an entertaining yet informative article.
References
Alvarez LW. Alvarez W, Asaro F and Michel HV. 1980. Extraterrestrial Causes for the
Cretaceous-Tertiary Extinction. Science. 208(1):1095-1108.
Arvidson R, Drozd R, Guinness E, Hohenberg C, Morgan C, Morrison R and Oberbeck
V. 1973. Cosmic ray exposure ages of Apollo 17 samples and the age of TYCHO.
th
Proceedings of the 7 Lunar Science Conference; 1976 March 15-19; Huston, Texas.
New York: Pergamon Press Inc. 3(1):2817-2832.
Bottke WF, Vokrouhlicky D, Bro M, Nesvorny D, and Morbidelli A. 2001. Dynamical
Spreading of Asteroid Families by the Yarkovsky Effect. Science. 294(1):1693-1696.
Bottke WF, Vokrouhlicky D, Rubincam DP, and Nesvorny D. 2006. The Yarkovsky and
YORP effects: Implications for asteroid dynamics. Annual Review of Earth and
Planetary Sciences. 34(1): 157-191.
Bottke WF, Vokrouhlicky D, and Nesvorny D. 2007. An asteroid breakup 160 Myr ago
as the probable source of the K/T impactor. Nature. 449(1):48-53.
Broź M. 2006. Yarkovsky effect and the dynamics of the Solar System[Doctoral Thesis].
Prague: Charles University.
Hildebrand AR, Penfield GT, Kring DA, Pilkington M, Camargo AZ, Jacobsen SB, and
Boynton WV. 1991. Chicxulub Crater: A possible Cretaceous/Tertiary boundary impact
crater on the Yucatan Peninsula, Mexico. Geology. 19(1): 867-871.
Menichella M, Paolicchi p, and Farinella P. 1995. The main belt as a source for NearEarth Asteroids. Earth, Moon, and Planets. 71(3): 133-149.
Russell DA. 1979. The Enigma of the Extinction of the Dinosaurs. Annual Review of
Earth and Planetary Sciences. 7(1):163-182.
Trevisan M. 2007 Sept 6. Far-flung asteroid crash doomed the dinosaurs. Globe and
Mail. Sect. A:19.
Appendix A
Far-flung asteroid crash doomed the dinosaurs
Matthew Trevisan. The Globe and Mail. Toronto, Ont.: Sep 6, 2007. pg. A.3
2007 CTVglobemedia Publishing Inc. All Rights Reserved.
A collision involving two massive asteroids between Mars and Jupiter caused a fragment to eventually slam
into Earth, scientists say
An asteroid that is believed to have wiped out dinosaurs and other life forms after smacking into Earth 65
million years ago may have been part of a much larger asteroid involved in a massive collision about 160
million years ago.
In a paper published today in the influential science journal Nature, William Bottke and colleagues argue that a
chunk of asteroid that broke off from a collision in the innermost region of the asteroid belt encountered a
gravitational pull that drew it toward Earth over a period of tens of millions of years, eventually smashing into
the Yucatan Peninsula, forming the Chicxulub crater and likely causing the extinction of the dinosaurs.
"It shows that events that happen far away from the Earth can still have a significant influence on essentially
the biological evolution, and, to some degree, the geological evolution of the planet," said Prof. Bottke,
assistant director of space studies at the Southwest Research Institute in Boulder, Colo.
Using computer simulations and mathematical calculations, Prof. Bottke, David Vokrouhlicky of Charles
University in Prague and David Nesvorny of the Southwest Research Institute were able to retrace the orbits of
hundreds of asteroids back to their locations before the collision 160 million years ago - give or take 20 million
years - and found that hundreds of asteroids may have come from one parent asteroid.
"If you look at how far the asteroids have travelled, you can use that distance like a clock to tell you how old the
breakup is," he said.
The researchers believe that the parent asteroid was 170 kilometres in diameter and crashed into another
asteroid 60 kilometres in diameter in the innermost region of the main asteroid belt between Mars and Jupiter.
The collision happened about 200 million kilometres away from Earth.
Little is known about what happened to the smaller of those two asteroids, Prof. Bottke said, but the bigger one
formed the Baptistina asteroid family, exploding into 300 asteroids larger than 10 kilometres in diameter and
140,000 asteroids larger than one kilometre wide.
"We found that there was a very high likelihood that one of the largest fragments that escaped out of the
asteroid belt ended up hitting the Earth," Prof. Bottke said.
That happened, he believes, by what astronomers call the "Yarkovsky effect," whereby asteroids absorb
sunlight and re-radiate the energy as heat. The small amount of extra energy moved the asteroid in small
increments over a process of tens of millions of years to dynamic regions in the solar system called
resonances.
Here, Prof. Bottke said, the asteroid came under stronger gravitational influence by Mars and Jupiter, which
knocked it off its orbit, and on to a path that would eventually collide with Earth - but not before wandering for a
few million years in space.
The researchers used research from the past 10 years to determine that the composition of the Chicxulub
crater, made of carbonaceous chondrite, matched what they believe to be the composition of the parent
asteroid.
They believe that there is a "more than 90-per-cent" probability that the asteroid that created the Chicxulub
crater came from the Baptistina parent. Prof. Bottke said there is also a 70-per-cent probability that the lunar
crater Tycho, which was formed 108 million years ago when an asteroid slammed into it, was formed by a
Baptistina asteroid.
The next step for researchers will be to test the composition of the craters on Earth from 80 to 100 million years
ago. "If they come up with a composition similar to the composition that made the [Chicxulub crater], our model
looks pretty good," he said. "If they come back with lots of different compositions, then our results are more
suspect."
Prof. Bottke said that according to his research, a collision similar in scale to the asteroid that struck Earth 65
million years ago happens once every 350 million years. A collision similar in scale to the one that occurred in
the asteroid belt 160 million years ago happens once every 200 million years.
The collisions are random, he added, not unlike shaking a box of marbles around and having two bigger
marbles collide at the same time.
"It reminds us that we live in a kind of shooting gallery," said Philip Stooke, a geography professor at the
University of Western Ontario.
"The planets are buzzing around the sun and people used to think that everything is stable and it's been like
this for billions of years but actually it's not," he said. "And we live in this environment where things are zipping
around between the planets all the time."
Martin Duncan, a Queen's University astrophysicist, said the discovery satisfies the curiosity in humans.
"We like to know more about our past," he said. "We'd like to know more about the major events that influenced
life on Earth. We'd like to know more about the current hazards and kind of the future probability of events like
this."
The big crunch
Scientists using computer modelling have tracked down the origins of the asteroid thought to have caused
Earth's mass extinction 65 million years ago. "The K/T impactor" was spawned in a collision in the main
asteroid belt nearly 100 million years earlier.
THE COLLISION THAT STARTED IT ALL:
An asteroid estimated to be 60-kilometres in diameter....
...hit another asteroid that was approximately 170-kilometres in diameter
Which created the Baptistina asteroid family, a cluster of fragments thought to have 140,000 bodies larger than
1 km.3
This breakup may have caused the moon's 85-km Tycho crater.
A larger fragment from the Baptistina breakup created the 180-kilometre Chicxulub crater off the coast of the
Yucatan 65 million years ago.
The Chicxulub crater, the event that marked the sudden extinction of the dinosaurs as well as the majority of
life on Earth, was made when an object, 12-15 km in diameter, hit the planet. The crater was bowl-shaped, and
100 km in diameter and 30 km deep, but collapsed quickly to create today's structure.
SOUTHWEST RESEARCH INSTITUTE/THE GLOBE AND MAIL
SOURCE: NATURE