Demystifying the Giant Magnet We Call Home

40

A basement hallway of the Norris Chemistry Building is lined with peculiar caution signs about Occidental’s multi-million dollar nuclear magnetic resonance spectrometer. The Moore Laboratory acts as a scientific cemetery for the world’s largest Mexican bird collection. A room in Hameetman Science Center designed to have virtually zero magnetic field houses a cryogenic magnetometer and thermal demagnetizers.

After two years of taking science classes in these buildings, I still knew little to nothing about the college’s impressive scientific assets. I merely hoped that these mysterious things stood at the center of scientific research of an equally impressive caliber.

I decided to investigate. This pilot blog, Tiger Lab, attempts to uncover the mysteries lurking in our science labs and elucidate student and faculty research both on campus and abroad.

Episode 1: Demystifying the Giant Magnet We Call Home

Geology Professor Geoff Cromwell and student researchers Jordan Bretthauer (junior) and Cole Valentino (junior) traveled to Anchorage, Alaska this summer to investigate a theory that could quite literally shift the world as we know it.

Photo courtesy of Mel Devoney
Photo courtesy of Mel Devoney

Bretthauer and Valentino took Paleomagnetism with Cromwell Spring 2015. According to Valentino, Cromwell explained a project he was planning for the summer and asked if anyone was interested assisting his research.

“This opportunity allowed me to take what I was learning in the classroom and apply it to a real world applicatio

n, outside the classroom,” Valentino said.

With such an opportunity, and the allure of 22 hours of sunlight during the Alaskan summer, both students easily hopped on board.

“We told him we were interested in research after class one day,” Bretthauer said. “And he asked if we wanted to go to Alaska.”

Cromwell recruited Bretthauer and Valentino with the intent of collecting samples taken from lava flows from the Aleutian Islands—volcanic islands created from the subduction zone near Alaska between the Pacific and North American plates.

“The purpose of this research is to figure out what the magnetic field was doing in the Aleutian Islands over the last million years,” Cromwell said.

Let’s backtrack to the notion of Earth’s magnetic field. We all know that a compass simply always points North, but the explanation for why this is true is slightly more complicated.

Emanating from its molten outer core, the Earth’s magnetic field extends into space to form the magnetosphere, which acts as a shield to protect the Earth from harmful cosmic rays. The flow of molten iron in the core generates electric currents that produce magnetic fields. Scientists currently believe that the overall field takes the form of a dipole—acting like a bar magnet with one positively and one negatively charged end—at a tilt of about ten degrees from Earth’s rotational axis.

In the outer core, molten iron alloys affect a change in the magnetic field over long periods of time. At irregular intervals averaging several hundred thousand years, the Earth’s field reverses and the North and South Magnetic Poles switch places. Paleomagnetisms utilizes the magnetic record left behind in rocks to help explain motions of continents and ocean floors in terms of plate tectonics.

However, geologists studying paleomagnetism have recently run into some complicated findings.

According to Cromwell, modern day measurements show variations from the accepted dipole model of the Earth.

Scientists generally believe that, while the Earth never momentarily depicts a perfect dipole, global measurements average out into a dipole over a range of a hundred thousand to millions of years. However, studies in regions such as Iceland and Antarctica shook their confidence. The magnetic record in rock samples from these regions suggest that the accepted dipole model may not hold true at all latitudes.

Cromwell set out to investigate if other locations showed this variation.

According to Bretthauer, Cromwell received funding from the National Science Foundation to initiate this research. She was excited to join a project that lacked previous research.

“In terms of the paleo-magnetic world … there’s a lot of information that has been collected from North America, the United States, Europe, some in South America,” Cromwell said. “But at high latitudes in the Arctic and Antarctic, there’s not that much material because it’s hard to get to, it costs money and logistics. So this really benefits the paleo-magnetic community because there’s been no systematic study like this in the Aleutian Islands.”

Cromwell, Bretthauer and Valentino set off for Anchorage to collect samples from three volcanoes within an approximate range of 1500 kilometers of the Aleutian Islands chain— Tanaga, Akutan and Aniakchak.

The United States Geological Survey (USGS) had already dated the lava flows on these islands very meticulously and stored volcanic rock samples in a warehouse in Anchorage.

USGS researchers had drilled the rock samples out of the volcanoes and measured the direction and angle of those drill cores in order record the original orientation of the magnetic minerals in the lava flow.

Lava flows are composed of magnetic minerals — primarily magnetite. When those minerals erupt out of a volcano in lava at temperatures near 1000 degrees Celsius, those freely-moving magnetite grains act as “compass needles” that orient in the direction of Earth’s magnetic field. Once the lava cools, these compass needles are frozen in time, holding a magnetic memory in the rock.

Cromwell, however, is not interested in magnetic direction, but the strength of the magnetic field.

The three researchers scavenged through lava rocks in the warehouse to find samples that would be appropriate to bring back to Occidental’s cryogenic magnetometer — an instrument used to measure the strength and direction of magnetization.

For three days, Cromwell’s team chipped off about 100 pea-sized samples from about 100 lava flow rocks in the U.S.G.S. warehouse. The samples date back a couple thousand to about 500,000 years old.

“We’d get up, have a nice cup of coffee, and go to the warehouse in Anchorage,” Cromwell said. “We spent about two full days getting dusty and dirty and digging through boxes.”

Once Cromwell’s team made it back to Occidental, the samples were set up for experiments in a small magnetically-shielded room in Hameetman Science Center’s paleomagnetism laboratory. To secure accurate magnetism measurements, the room is protected by two layers of high-permeability steel separated by a one-foot airgap, composing a wall magnetized so that the earth’s field (about 60,000 nano-teslas) is reduced to a few hundred nano-teslas inside the room.

Brettaheur and Velntino have passed the samples from the Akutan Island on to Michael Stevenson (senior), now that their job is done.

“My job is to run these samples in the lab using our magnetometer and analyze the subsequent intensity data,” Stevenson said.

“I chose to help with this project because A, Oxy happens to have an incredible paleomagnetism laboratory and B, this type of research is relatively new — so I feel that as an undergrad, it’s pretty exciting to have the opportunity to work in an emerging scientific field.”

Andrew Benedict Phillip ’15 worked on Tanaga Island samples over the summer.

According to Cromwell, it takes about 35 heating steps to unlock the magnetic record of each rock. The magnetometer can measure 48 samples at a time, so it takes about two weeks to get a record of one set of 48 samples.

So far, the results have been unsatisfactory for Cromwell.

“What we’ve found out so far is that a lot of our samples aren’t working very well,” Cromwell said.

Fine-grain crystal samples respond best to paleo-intensity experiments, but the USGS collected rocks with larger crystals which, according to Cromwell, are perfect for geochemistry work but unfavorable to unlocking magnetic properties.

However, he is optimistic about the remaining 30 percent of samples they have not yet tested.

“It’s very possible that many of those may end up working,” Cromwell said.

Since plate tectonic reconstructions are based on how the magnetic field behaves and whether or not the North Pole actually sits at the spin axis, any variation from the dipole model that Cromwell may discover could require geologists to reevaluate their model of global plate tectonics.

If the preliminary experiments are successful, Cromwell will run more in-depth experiments on the samples that responded best. Ideally, he would bring a team to the Aleutian volcanoes that provided the best data and collect the preferred fine-grained volcanic glass as early as next summer.

Whether this summer’s samples yield successful data or not, both Valentino and Brettahuer found the experience valuable and enjoyable.

“Alaska was beautiful and it was really cool to get to see the USGS [and] work closely with geologists there,” Bretthauer said.

She valued learning about the inner-workings of the USGS and getting a glimpse of geology career paths outside of academia.

“One of my favorite parts of the trip was getting a tour of the USGS Alaska Volcano Observatory from a USGS scientist,” Valentino said.

They toured the observatory control room, in which scientists monitor the activity of over 20 volcanos on the Alaskan Peninsula and in the Aleutian Islands.

Bretthauer and Valentino were also able to explore outside of the warehouse in a hike around Anchorage on the third day of the trip. They both stuck around Alaska for a couple more days after completing the sampling to go to the Solstice Festival in Anchorage June 20.

“It was an excellent week to be in Anchorage between the weather, and annual marathon and festival,” Valentino said. “The Solstice Festival was a great taste of the local atmosphere. A series of local bands played at a park in downtown. They even had reindeer sausage food carts!”