Mauritia: what is a “microcontinent,” and what is an “island?”

National Geographic’s recent article outlining the discovery of what geologists are calling a “microcontinent” that has been submerged for 85 million years sparked a small controversy on my Twitter feed. That being, what exactly makes a “microcontinent” different from any old island? If the definition of an island is a land mass surrounded by water, then a microcontinent almost surely seems to fit the description. So what is the difference?

Well, if you want a question like that answered, you have to ask a geologist. And if you’re going to ask a geologist, why not ask the geologist who happens to be a co-author of the study that started it all?

Bjørn Jamtveit of University of Oslo in Norway responded to my email request with the kind of stunning swiftness that has always made me love the Internet. The answer, he says, has less to do with islands and much more to do with continents:

Geologists talking about continents do however refer to something that is made up of continental crust (which is chemically and physically different from oceanic crust – which makes up most of the sea floor) and not size.

Via Physical Geography, a graphic displaying the component parts of the “lithosphere,” including continental and oceanic crust.

In other words, while islands can be any land mass surrounded by water, in order for something to be considered a continent, geologically speaking, it must be made of the same rock as other continents. The difference is that oceanic crust is made up of volcanic rock: heavy, dense rock called basalt. The oceanic crust is basically that part of our Earth’s crust which is left after volcanic eruption pushes the continents apart. Continental crust, however, is largely made up of granite.

Geologists refer to oceanic islands, meaning islands which have been formed by volcanic activity. Here again, we have a very specific definition and of course we would expect the oceanic island to have lots of basalt. In the case of Mauritius, Jamtveit and his team believe that the presence of both basalt rock and older, granite rocks and the mineral zircon indicate that part of an older, very small continental crust also forms the island.

Thus the research suggests that, while Mauritius has long been considered an oceanic island, the truth may be that it was formed on the rubble of an older shard of continental rock.

This Week on Mars

Martian blueberries, dry ice snowfalls and Curiosity tests robotic arm

The rate at which we are getting data back from Mars continues to amaze me. We have two working robots on the surface of Mars, plus the Mars Reconnaissance Orbiter, all beaming back new information in what seems like daily increments. With that in mind, I thought I’d summarize the current state of the Mars project as it happens.

“Blueberries” and.. not “blueberries”:

A subject on which I’m just catching up now. Apparently, the Mars rover Opportunity has been studying what scientists have nicknamed “blueberries” on the surface of Mars since it landed. The blueberries are actually round pellets of iron-rich sedimentary rock that scientists believe were formed when Mars still had liquid water on its surface.

But what Opportunity has discovered nowis a bit of a mystery. They look similar, but apparently have a completely different composition. Scientists used a laser spectrometer to analyze the contents and discovered that the new spherules have concentric spheres of composition. “They seem to be crunchy on the outside, and softer in the middle,” says Steve Squyres of Cornell University.

So… apparently, Mars is the Home of the Whopper? Time will tell..

Dippin’ Dots, my ass.

Curiosity flexes its arm:

Curiosity continues to go through system-wide diagnostics as it preps for its mission. One major component of the Mars Curiosity Rover is its robotic arm, loaded to the gills with scientific whiz-bang. Since September 5th, JPL engineers have been testing out the 7 foot long arm and its tools, getting ready for Curiosity to touch its first Martian rocks.

The robotic arm includes the Alpha Particle X-Ray Spectrometer (APXS), which is the same technology Opportunity used to test the composition of the blueberries. The arm is also equipped with a camera which it can use to take close-up, color photos of rocks. The press release notes that this is the fifth week of a two year mission, but doesn’t say what the next step will be.

Let it snow, let it snow, let it snow!:

For those of you dreading the oncoming Rochester winter, take heart! There is in fact a place with even shittier winters: the southern pole of Mars.

Scientists analyzing data from the Mars Reconnaissance Orbiter have discovered the best evidence yet that winter on Mars brings carbon dioxide snowfalls to its south pole. While scientists have known about carbon dioxide ice on the polar caps for decades, this represents the first time they’ve been able to show evidence that the atmosphere produces carbon dioxide clouds that grow thick enough to produce precipitation. Carbon dioxide, remember, freezes at -193°.

So, like, buck up, Rochesterians!

Rochester Science

U of R researchers map the “plumbing” of volcanoes and earthquakes

Magma – molten, pressurized rock that moves beneath our Earth’s crust – travels through channels which scientists from the U of R describe as “plumbing,” and by studying and understanding the map of these plumbing pipes, we may someday be able to accurately predict where the next volcanic eruption or earthquake might happen. That’s the focus of research done in the two spots where the mid-oceanic ridge system reaches dry land, where such studies are considerably easier.

The mid-oceanic ridge system is the (mostly) underwater series of ridges, mountains and volcanoes that are formed by the push and pull of tectonic plates on the surface of the Earth. Part of this system is the Ring of Fire, famed for volcanic activity. But beneath all that volcanic activity are channels of magma flowing from high to low pressure areas. When that flow is just right, it forces itself up and the result is a volcanic eruption or an earthquake or both. U of R researchers joined an international team to explore and understand these channels:

Volcanic Plumbing Provides Clues on Eruptions and Earthquakes : Rochester News

By analyzing images taken by the European Space Agency satellite Envisat, scientists were able to measure how the ground moved before, during, and after eruptions. Also, Ebinger and Manahloh Belachew, also from the University of Rochester, operated an array of seismographs that provided the depth and detailed time control to gauge the fracturing of the earth and the flow of magma from multiple eruptions in Afar. Using these data, the international team built and tested computer models to find out how rifting occurs.