Scientists Unravel One Of The Keys To Life On Earth — And It's Right Beneath Your Feet

blue globe.gif

David Bercovici

An idealized version of the earliest plate tectonics. The blue areas are the rigid plates. The red, yellow, and green areas are the boundaries.

Scientists are constantly on a mission to untangle how Earth alone among the planets was able to evolve complex life.

Scientists know that Earth's past internal movements of the tectonic plates under our feet make our planet one-of-a-kind — they trapped carbon dioxide which helped make our planet habitable.

A new study, published in the April 6 issue of the journal Nature, may have figured out the mystery of how these plates formed — and why only Earth has them.

Why plate tectonics is important

USGS

These are the Earth's major tectonic plates. The arrows show which way the boundaries are moving.

Plates cover the entire Earth, and their boundaries play an important role in geologic happenings. The movement of these plates atop a thick, fluid "mantle" is known as plate tectonics and is the source of earthquakes and volcanoes. Plates crash together to make mountains, such as the Himalayas. They leave trenches where one slips beneath the other. They make giant rift valleys and ridges when going their separate ways.

The process is actually very important to life on Earth. Several billion years ago, the surface of our Earth began forming into puzzle pieces called plates. This process trapped our atmospheric carbon dioxide into rocks and stabilized our climate, making Earth habitable.

A Mylonite mystery

How this developed has been a mystery for centuries. But one feature present at all plate boundaries could be the clue needed to crack the mystery: a rock called mylonite.

Mylonite rocks show up at every plate boundary and have puzzled scientists since at least the late 1800s.

"Their presence is a bit of a mystery," study researcher David Bercovici, of Yale University, told Business Insider. "There are well-known observations of mylonite at all different kinds of plate boundaries and there's been a long debate about what causes them."

Wikimedia Commons/ Woudloper

Mylonite from the Southern Alps

Mylonite is a highly deformed rock, which makes it the size of a small piece of grain. Small grain-size equals a weaker rock. Since these rocks occur around all plate boundaries, their deformation and subsequent weakness piqued Bercovici's interest.

"It was a big motivation for developing this theory in the first place," said Bercovici who worked with Yankick Ricard of the Université de Lyon on the study.

How rocks define Earth's plates

David Bercovici

Using a set of laws to describe how grains evolve and "many many pages of physics," Bercovici and Ricard were able to calculate how the birth of plate tectonics may have come about. Bercovici began with the idea that, back when Earth was just a ball of hot goo, certain parts of the surface would become cooler than others and sink. These areas were called downwellings. "You can see this happen in a cup of coffee or soup," he said.

Downwellings cause deformation of the sinking material as it bends downward. In the globe to the right, the blue is a sinking area on the Earth's surface, the beginnings of a plate boundary.

"The idea of our model is that if I deform a rock, I'll actually make the grains smaller." Smaller grains equal weaker rock and a weaker rock means it will more easily succumb to future deformations.

David Bercovici

This creates a feedback loop where Earth's slowly cooling crust accumulates weak zones. "And you accumulate enough of these weak zones and you'll eventually get plate boundaries," he said.

In the globe to the right, the sinking from the red globe above has created a convergent boundary — in blue — where plates move together. This pulls on the rest of the Earth's surface, eventually forming a divergent boundary — in red — where plates move away from each other. Once a piece of Earth's surface is enclosed by boundaries, it becomes a moving plate.

On Venus, damaged areas of the crust were never able accumulate into boundaries because it was too hot. The weak zones healed relatively quickly and the planet was never able to develop plate tectonics.

Venus' plates never trapped CO2, never cooled, and the impact on the planet's atmosphere makes it uninhabitable.

Solar Eclipse: May 20, 2012

Click on image to enlarge

Reflection on My Reflection

While working with the software for the digital reflection, I began to really appreciate the ease at which "live" lessons could be recorded by teachers to enhance student understandings. Although I haven't done it yet, I plan to record future graphic presentations (fancy term for PowerPoint), and have them available for my students who might miss the actual presentation because of illness or other legitimate reason for an absence. I also have to thank Jeff for explaining how easy it is to resize embedded information in our blogs on that first day of class, because I had to recall that information to neatly fit my digital presentation in the space available. Thanks again to all who helped me increase my techknowledge (pun intended) throughout the semester.  -Carl

Digital Reflection

Student Seating and Classroom Management

Another seemingly obvious epiphany that I had recently is how important something as simple as how the seating in a room can affect student participation and lesson comprehension. Most science classrooms are designed around desks, and they invariably force students to sit at odd angles in relation to where most of the instruction takes place. I understand the need to have student-centered learning, however, having students facing away from the focus of instruction does very little for a 14 year-old’s comprehension. The standard single seats from the 70’s and 80’s seem to be traded out at an increasing rate for more social desk groupings. This is even taking place in non-science classrooms. I have recently discussed this issue with one of my cooperating teachers, and he stated that he can understand my point of view, especially considering the few number of labs we do that require desk usage. With the fundamental purpose of teaching being the transfer of understandings to our students, I feel that anything that promotes this idea should be embraced. The classes I am teaching this semester are all taking place in portable rooms that have no distinct designation between Social Science, English, or Earth Science. However, the classrooms where science isn’t being taught all have conventional single seating, and those teaching science all have table group seating.

            I see the benefit of having tables available for students while conducting lab work, but during the other 80% of their time in the classroom, the table group seating works against their ability to remain focused. Having experimented with multiple table arrangements over the past school year, I have seen how quickly students drift away from the central focus of the lesson when they are staring directly at another student. Some of my best students have been distracted by students around them when seating assignments and arrangements change. Unfortunately, I don’t see any one correct answer to this problem. Limited space and larger numbers of students in every class will likely just exacerbate the problem. Facing a student in any direction away from the focus of learning is simply telling them that what is going on isn’t really important. Students know that the direction they are facing is where the information is, whether that information is content or socially based.

The Bottom Line

Over the past six months of teaching I have frequently reminded my students and occasionally myself what the reason is for them being in my class. It isn’t to get good grades, nor is it to please their parents. The reason that seems to get muddled by all of its byproducts is the attainment of knowledge and understanding. I know this sounds obvious and simple, but it is amazing how often we lose sight of this while interacting with students. I completely understand that students want to get good grades. I strive for this as well in any class I am enrolled in. But when I remind students that learning is the true reason why they are in the seats, they look at me like I am inconveniencing them with some silly fact.

            The reason I need to occasionally remind myself about this, is that sometimes a student might ask me a question that isn’t directly connected to the lesson being taught, but is nonetheless a valid inquiry based on a real desire to know more about a particular subject. With time always being a commodity I am short of, I will try to give a brief answer that I think satisfies the student’s question and quickly move back to the subject at hand. This particular scenario came up just the other day when I was discussing the distances between stars and the speed of light. I had a student ask me about my feelings on UFOs and whether I thought we might ever visit other solar systems. I answered the question which was asked, but looking back, I feel I may have missed a tremendous opportunity to provide additional information, not just to this student, but to the entire class. My simple answer of the distances being so vast could have been better executed if I were to go through the math of question. I could have had the class, as a group provide the information about how far light travels in a single year (approximately 5.9 trillion miles), and let them decide whether they felt we would ever make such a journey. Instead, I was focused on cramming the last few hours of review in prior to their CST exams and potentially lost a teaching/learning moment that might have lasted them the rest of their lives.