REFLECTIONS ON PEDAGOGICAL AND CONTENT INFORMATION/RESOURCES RELATED TO THE PROJECT
Asteroid 2005 YU55, (for the year and month when it was discovered) passed near the Earth- closer than the moon- on November 8, 2011, as reported at http://www.cnn.com/2011/11/08/opinion/urry-asteroid-earth-risk/?hpt=hp_bn9. This asteroid posed no threat this time. However, a large asteroid hitting the Earth could cause global catastrophe. So, as Meg Urry, Israel Munson professor of physics and astronomy and chairwoman of the department of physics at Yale University, points out NASA has a Near Earth Object Program to track potential collisions.
Vesta is much smaller than the asteroid that created Chicxulub- the crater near the Yucatan that is reported to have caused the mass extinction of the dinosaurs- but it could damage a city or cause a tsunami. Scientists are studying how to prevent a collision if an asteroid were found to be on course with the earth; they would need to alter its trajectory somehow.
NASA's WISE infrared satellite suggest there are roughly 500,000 near-Earth objects with diameters of 50 to 100 meters with an estimated impact frequency of one every thousand years. “Scientists think the famous Tunguska event of 1908, an enormous explosion that flattened 80 million trees over 830 square miles (2/3 the size of Rhode Island) in Russia, was caused by an impact from an asteroid or meteorite about 50 to 100 meters in diameter. The force of this explosion was roughly 1,000 times larger than the nuclear bomb dropped on Hiroshima.”
In severe budget cutting times, how much money will be reserved to continue studying asteroids? How big of an issue is it to protect the planet? Can we afford to not pay attention or are other problems more pressing- like will our population increase sooner doom human life on earth? As someone who studies natural hazards, I find it interesting that impacts with extraterrestrial objects can strike the earth anywhere- there are no regions at higher or lower risk than others and the potential impacts will be global, when a big one eventually hits. The pitted moon is our visual reminder that it is only a matter of time. Meanwhile we’ll continue to cope with the impacts of all the other natural hazards affecting our dynamic earth. Vesta is another reminder of what is to come eventually.
I find it interesting in the NOVA Megabeasts' Sudden Death show, (http://www.pbs.org/wgbh/nova/evolution/last-extinction.html -March 2009, 52 minutes), the program description on the website refers to a "startling hypothesis that may finally explain" the extinctions of the megafauna in North America 12,900 years ago. Yet in the opening comments of the movie they refer to the idea as a theory. As a scientific educator, I find it interesting to explore the distinction between different terms- hypothesis versus theory- especially in this case, because unraveling the confusion teaches one about the nature or process and history of science.
Theory and hypothesis generally are not interchangeable terms for a scientist; a theory implies that something has been proven and is generally accepted as being true. For many scientists, in the case being discussed, they don't feel there is enough "evidence" to accept the idea that a comet caused the end of the megafauna in North America 12,900 years ago. When it comes to active and new explanatory ideas in science, the line between hypothesis and theory can become blurred. Maybe this is when a "hypothetical theory" becomes a useful term?
For the layperson, a "theory" can mean just a "guess", but not to scientists, where a theory is an explanation of a set of related observations or events based upon proven hypotheses and verified multiple times by detached groups of researchers. Students watching this video and exploring the topic can be challenged to seek and keep track of the "evidence"- all the data that supports the comet hypothesis and then determine why the idea is not yet universally accepted and what it would take to have the "hypothesis" become a "theory".
Generally theories are well documented and proved beyond reasonable doubt. "Yet scientists continue to tinker with the component hypotheses of each theory in an attempt to make them more elegant and concise, or to make them more all-encompassing. Theories can be tweaked, but they are seldom, if ever, entirely replaced," (http://www.wilstar.com/theories.htm). Is this the case with the comet theory described in the movie? Listen and take note of key language being used, like, "Today, a controversial new theory just might explain" the extinction of the megafauna. Ask why is the idea controversial, because it is new, or because it doesn't yet explain everything about the mystery?
The Tunguska event, described by an eye witness account, is another airburst theory similar to the one proposed to have brought about the extinction of the mega fauna and Tunguska also remains unresolved.
The odds are estimated that an event like the size of the explosion of an asteroid or comet that occurred over remote Tunguska, Siberia, in 1908 will occur one in 200 years to one in 1,000 years. This was the largest impact of a cosmic body with earth in human recorded history. If we're lucky, scientists will stop the next such event before its occurrence; many preventive strategies are being researched. The mystery of Tunguska is that no one has found remains of any impact object or a crater, just evidence of a 2,000 square kilometer area of flattened trees, which is why the "airburst" theory developed. A dirty snowball comet made up of dust and ice might have been the culprit. A competing theory is that a rapid combustion of methane gas was released from the swampy ground. International scientists are still investigating however.
In June 2008 Scientific American Magazine ran an article on the centennial anniversary of the event about a team that was returning to the site. The scientists were looking for evidence for their hypothesis that nearby Lake Cheko was the impact crater. An acoustic-echo sounder from an earlier trip revealed a trace of a dense, meter size object, (possibly of extraterrestrial origin?), buried in the lake sediments. A magnetic anomaly from a magnetometer survey also turned up in the same spot. What has been the outcome of the 2008 trip where the team was loaded with a suite of the latest equipment including ground penetrating radar capabilities, an underwater camera, and sediment coring devices? I'll need to scour the literature to find out if this ~100 year mystery has come closer to being solved (Gasperini, Luca et al., "The Tunguska Mystery" in Scientific American, June 2008, p. 80-86).
I include this story because it's another example of how science evolves through an interdisciplinary approach. There is more data to be gathered, and as technology advances and more research occurs, more answers will be found. Science is an enticing career choice for this reason.
(Refer to the History Channel youtube video: http://www.youtube.com/watch?v=EiXpp-i442s.)
I thought I had gathered a good collection of resources on this site for teachers, when I discovered, serendipitously, a book by Clyde Freeman Herreid, a science professor, who is so captivated with stories and convinced of their importance for learning, that he edited a book, Start with a Story: The Case Study Method of Teaching College Science, 2007, National Science Teachers Association Press, Arlington, VA. Included in this great treasure trove is a story, "Of Mammoths and Men: A Case Study in Extinction" by Nancy A. Schiller and Clyde Freeman Herreid, p211-218. This four page case study, with an additional four pages of teaching notes, reads like an engaging movie script with the opening scene taking place on an airport tarmac where a frozen mammoth is being flown in by helicopter from where it’s been extracted from its "snowy grave" (based on an actual discovery in 1999). After being exposed to the engaging story, students then research evidence for and against the various hypotheses and meet to discuss the merits of each.
Schiller and Herreid's activity addresses the questions of what happened to the mammoths and Neandertals and is similar in pedagogical style to the jigsaw group activity developed by my graduate students and me. They also address our theme of exploring impacts and extinctions, however, Schiler and Herreid's case study was developed for biology courses which include a section on evolution. With all of the guidance provided in his book, on how to develop and use good case studies effectively to teach, Herreid has inspired me to write my own case studies to more directly target the key concepts in our "Exploring Four Earth Science Enigmas" learning unit. I encourage anyone interested in our topic to share their ideas, which you can do on this site, at the bottom, under "Feedback". Asking students to write case study is a great assessment exercise; that allows them to be creative. Under the "Teachers Resources" section on this site, you'll find, "Assessment Activity", adaptable for grades 8-16, which incorporates many of the instructional points recommended in Herreid's book. The ideas for this assignment and accompanying rubric were modified from Schiller and Herreid's "Classroom Management" section, p. 217-218.