science – Page 7 – Montessori Muddle

How Microscopic Shells can tell us the History of the Earth’s Climate

cc-fossil-ice-0410 — Seeing the bigger picture.

Looking at the smear slides of Coon Creek Sediment Matrix got me thinking about just how important these little, microscopic shells have been for what we know about the Earth’s past climate. In fact, they provide the background knowledge that we have about the changes in climate that we’re seeing today.

ocean_dr — Deep sea drilling vessel, JOIDES Resolution. Image via the National Science Foundation.

Back in the 1970’s the Deep Sea Drilling Project collected a lot of sediment cores from all around the world. The deeper you drill under the sea bed the older the sediments are, so micropaleontologists could look at how the organisms that lived in a certain area changed over time. Certain forams that could only live in warm oceans were found living far to the north. By combining all the information from all the sediment cores, they could construct paleo-geographic maps showing what the climate was like in the far past. It’s one of the reasons we know that the Jurassic climate was a lot warmer than today’s climate.

Then they invented mass spectrometers.

Mass specs can find the mass of individual atoms. Calcium carbonate has the chemical formula CaCO₃. Water, as we should know by now, is H₂O. They both have oxygen atoms, but not all oxygen atoms are equal; some are more equal. Actually, the mass of any atom is made up of the mass of the protons plus the mass of the neutrons in its nucleus. Now, by definition, any atom with eight protons is oxygen; however, while oxygen usually has eight neutrons, it sometimes has nine or even ten.

Your standard oxygen, with eight protons and eight neutrons has an atomic mass of sixteen, and is written as ¹⁶O or oxygen-16. Well, oxygen with ten neutrons is going to have a mass of eighteen (8p + 10n) and be called oxygen-18 (¹⁸O). These different versions of the same element are called isotopes.

oxygen-18 — Oxygen-18 has two more neutrons than the much more common oxygen-16. Note that both atoms have eight electrons, but their masses don't count because electrons are really small compared to the protons and neutrons which have about the same mass.

water-20 — Water molecule with a molecular mass of 20.

What does this have to do with climate? Well a water molecule with two hydrogen atoms, each weighing one atomic mass unit, and one oxygen-16 atom will have a molecular mass of 18, while a water molecule with an oxygen-18 atom will have a mass of 20. When water evaporates from the oceans, the water with the lighter isotope will have an easier time going from liquid to a gas in the atmosphere.

So, during an ice-age for instance, lots of water evaporates from the oceans, falls on land as snow, and then gets trapped in the enormous glaciers that cover entire continents. Since the lighter water molecules evaporate easier from the oceans, they’re the ones that will end up falling as snow and being compressed into glacial ice. The water molecules left behind in the ocean will tend to have the heavier oxygen-18 isotopes. Since the forams use the ocean water as part of the process of creating their calcium carbonate shells, the oxygen from the water ends up in the carbonate (CO₃) of the shells. Since the ocean water has extra oxygen-18s during an ice-age, then the shells will have extra oxygen-18 isotopes during an ice-age.

larsenc_ice — Ridge of ice from the continental glacier in Greenland. Glacial ice will have lighter isotopes than the oceans the water originally evaporated from.Image by Konrad Steffen from the U.S. Antarctic Survey.

Therefore, by measuring the amount of heavy oxygen-18 isotopes that are in a single shell, we can tell how large the glaciers were at the time that shell formed, and tell what the global climate was like.

Of course there are some interesting complexities to the story, but that’s the general idea of how the microscopic shells of long-dead plankton can tell us about the history of the Earth’s climate.

Coon Creek Matrix Under the Microscope

cc-fossils-0410 — Hunting for microscopic fossils at the dinner table. Inside the circle is 100x magnification; outside the circle the magnification is 1.

My students will tell you that I’m never happier than when I have my cup of tea. On the night after our visit to Coon Creek, I put a tiny sample, about the size of a matchstick’s head, of sediment matrix on a microscope slide, and added a drop of water to disperse the grains. Then I sat there, while the chaos of dinner-making swirled around me, and searched for tiny, microscopic fossils of creatures that died long ago. With my cup of hot tea beside me, it was like sitting in the eye of a storm, flaming hamburgers be damned, a modicum of sanity in the asylum.

cc-quartz-microscope — Quartz grains from Coon Creek Formation sediment seen under the microscope at 100x magnification. Quartz is easy to identify because of the way it breaks with curved fractures.

The first thing I noticed though were the quartz grains. They’re very small, silt-sized, but are the largest grains in the sediment. They’re pretty easy to identify because they break like glass, with curved, conchoidal fractures. They’re also pretty little things under the microscope; little, sharp-peaked, transparent mountains.

cc-mineral-microscope — Other minerals are visible in the sediments. Though they're relatively large they're still dwarfed by the quartz (100x magnification).

Other minerals are visible in the slides, but they’re dwarfed in size and quantity by the quartz. Yet there is enough of the dark green, glauconite clay to bind the quartz grains together and protect the shells embedded in the sediment from dissolution by the universal solvent, water.

It’s interesting to observe these other minerals, because they take the more classic crystalline shapes and forms. The sharp edges are parallel to one another because of the alignment of the atoms in the mineral crystal.

cc-micro-snail — Snail like shape of what's probably a planktonic (lives in the water) foram. (100x magnification).

Finding the micro-fossils took a little patience. The entire slide had only four obvious specimens. Since they’re so small that meant a lot of going back and forth under the small field of view of the 100 magnification objective lens. They look like foraminfera to me, but it’s been a while since I’ve encountered them. Foraminfera, or forams for short, are tiny organisms that secrete beautiful calcium carbonate shells. They can be found in, or in the sediments beneath, most of the world’s oceans, particularly in the warmer areas.

Finding forams in the Coon Creek Matrix is a nice little exercise. One of my students, seeing what I was doing, wanted to try it too, so she made her own slide and searched until she found her own specimen. It was somewhat inspiring, so I’ve put together a more detailed post about finding microfossils.

We also found a neat little shell that looks like the overlapping scales on a pine cone. We were disconnected from the internet, so I was only able to look it up when I got back to school.

What looks like a type of boliviana foraminfera. It's benthic, which means that it lives in the sediments not in the water. — What looks like a type of bolivina foraminfera. It's benthic, which means that it lives in the sediments not in the water. (100x magnification).

Dr. J Bret Bennington at Hofstra has posted a nice PowerPoint of his introduction to marine microfossils lecture. As a basic introduction, it’s quite comprehensible to middle-school students, or people like myself who did not pay as much attention as they should have during that part of Paleontology. Anyway, based on these notes, the pine-cone-shaped thing is probably a variety of bolivina, a benthic foraminfera. The Foraminifera.eu-Project, is a wonderful, volunteer-produced resource for pictures and identifying forams.

Bolivina are benthic, which means they spend most, if not all of their time in the mud. Planktonic micro-organisms, on the other hand, spend their lives floating around in the water.

Foraminfera have calcium carbonate shells, as do clams and oysters. In the shallow oceans there is a slow rain of them that cover the sea-bed over the millenia. You can end up with thick layers. In fact, the white cliffs of Dover are white because of all the microscopic calcium carbonate shells. In the deeper reaches of the oceans there are much fewer of these shells because they dissolve under high pressure. As a result, down there you tend to find microfossils of diatoms and radiolarians, things with silica shells. Silica is that same material from which glass is made, and is the same material in quartz.

Finding microfossils has actually been quite important for understanding the history of the Earth’s oceans and climate. But that’s another story.

Drilling Through to the Mantle

Between 6 and 25 km thick, the Earth’s crust is an excruciatingly thin skin on a 6400 km globe. Yet even drilling to the bottom of the crust would require a remarkable feat of engineering. Some geologists want to try.

NPR’s Science Friday interviews Damon Teagle, one of the architects of the project. They want to drill in the ocean because oceanic crust is thinner than continental crust (on the other hand, it’s denser too, which is why it subducts).

Using different types of chocolate covered candy, they also have this wonderful video of the basalts, sheeted dykes and gabbros that make up the crust.

Coon Creek Immersion: Visiting the Cretaceous

cc-fossils-0391 — 70 million year old shell and its imprint collected at the Coon Creek Science Center.

Just got back from our immersion trip to collect Cretaceous fossils at the Coon Creek Science Center, and hiking in Natchez Trace State Park.

It was an excellent trip. Despite the cold, Pat Broadbent did her usual, excellent job explaining the geology of Coon Creek and showing us how to collect and preserve some wonderful specimens. Back at the cabins, we looked at some of the microfossils from the Coon Creek sediments (and some other microscopic crystals); similar fossils can tell us a lot about the Earth’s past climate.

Back at the Park, we traced a streamline from the watershed divide to its marshy estuary, and cooked an excellent seafood dinner as we learned about the major organ systems.

cc-red-snapper-01 — Dinner was delicious.

Our trip was not without difficulties, however. The group learned a bit more about self-regulation, governance and the balance of powers, as a consequence of “The Great Brownie Incident,” and the, “P.E. Fiasco.”

We were also fairly well cut off from the “cloud”: no internet, and you could only get cell reception if you were standing in the middle of the road in just the right spot in front of Cabin #3.

But more on these later. I have some sleep to catch up on.

View Coon Creek Immersion in a larger map

Life in Four Domains

journal.pone.0015530.g005 — The four domains of life, according to Boyer et al. (2010).

This wonderful, impressionistic image shows representatives of the three domains of life and large viruses, the proposed fourth.

This figure represents the living species in the four small pictures according to the current classification of organisms: eukaryotes (represented by yellow cell), bacteria (represented by green cell), Archaea (represented by blue cell) and viruses (represented by magenta colored Mimivirus).

— Boyer et al. (2010): Boyer M, Madoui M-A, Gimenez G, La Scola B, Raoult D (2010) Phylogenetic and Phyletic Studies of Informational Genes in Genomes Highlight Existence of a 4th Domain of Life Including Giant Viruses. PLoS ONE 5(12): e15530. doi:10.1371/journal.pone.0015530

Carl Zimmer has an excellent piece in Discover Magazine that summarizes the research, and sets out the new tree of life. Particularly important, is the fact that viruses can transfer genes with each other. The other domains tend to mix their genes during reproduction.

Growing up a Scientist

chromatography-column — I'm just intellectually curious.

Being a scientist is a state of mind. It’s really a way of looking at the world with wonder, curiosity, and logical rigor. Once you realize that, and get past the tedium of moving little bits of water from one place to the next, or peering through endless mathematical equations and lines of code, you’ll be a lot happier. At least that’s what I got out of Adam Rubin’s essay, “Experimental Error: Most Likely to Secede.”

His memories of growing up a scientist in middle school:

A scientist in middle school: Some of my classmates seem to have gotten large and confident very quickly. And the kids with the most friends are the ones who think science is lame. But I want friends. And I don’t think science is lame. Ah, the eternal question: WWDHD? (“What would Don Herbert do?”)1

Science questions explored: What is the difference between “weight” and “mass,” and why won’t you understand it no matter how many times it’s explained? What is static electricity, and why won’t you understand it no matter how many times it’s explained? What is a hypothesis, and why won’t you understand it no matter how many times it’s explained?

— Rubin (2011): Experimental Error: Most Likely to Secede

Selective breeding of foxes

Silberfuchs_06 — A silver fox. Image by Zefram via Wikimedia Commons.

Evan Ratliff has an excellent article that ties well into our discussions of evolution. It’s on the breeding of foxes to make them want human companionship, much the same way wolves were domesticated.

… researchers … gathered up 130 foxes from fur farms. They then began breeding them with the goal of re-creating the evolution of wolves into dogs, a transformation that began more than 15,000 years ago.

— Ratliff (2011), in National Geographic, Taming the Wild

domestication-pigs — Wild boar (top) versus a domesticated pig (bottom). Note the floppier ears, a trait common to domesticated animals. Figure from Darwin (1968).

It worked remarkably well, and not just with foxes, but with rats and mink as well.

The scientist in charge, Dmitry Belyaev, was looking into something that Darwin observed in 1868: domesticated animals are smaller, with floppier ears and curlier tails, than their untamed ancestors.

In terms that we’ve studied, domesticated animals all have similar physical characteristics (phenotype) and Belyaev wanted to find the genotype. His theory is that there is:

… a collection of genes that conferred a propensity to tameness—a genotype that the foxes perhaps shared with any species that could be domesticated.

— Ratliff (2011), in National Geographic, Taming the Wild