Earth’s magnetic field is decreasing rapidly, leading some to propose that it will undergo collapse followed by a return to its usual strength but in the opposite direction, a phenomenon known as a "polarity reversal" which last happened approximately 800,000 years ago. Such a collapse would have a potentially devastating effect on the ability of the magnetic field to shield us from cosmic ray bombardment. We will study how Earth’s magnetic field intensity changed during the last 5 million years and hope to determine whether the current decrease in field intensity is a common occurrence that does not necessarily indicate an upcoming reversal or whether it is indeed a rare behavior that will likely lead into the reversal of the magnetic field.

Specifically, we will take samples of 132 ancient lava flows of the Mount Erebus volcanic province in the McMurdo area that recorded the magnetic field intensity during their cooling from about 1000 °C to near-freezing. The Erebus volcanic province was formed over the last 5 million years in a wide area including Ross Island, Black Island, Mount Discovery, the Royal Society Range and the Dry Valleys.

We will sample these lava flows mostly in daytrips from McMurdo by snow mobile over the sea ice to islands and shoreline outcrops and by helicopter and hiking. We will take these rock samples home for analysis in the Scripps Paleomagnetic and Rock Magnetism Laboratory.

To a first order, the Earth’s magnetic field can be seen as a giant bar magnet the size of the earth and the magnetic field lines look a lot like the well known image of iron filings spread over a white paper with a bar magnet hidden below. However, this global “bar magnet” is caused by a different process in the liquid iron outer core. The churning iron combined with the Earth’s rotation creates a magnetic field that is approximately lined up with the axis of the planet around which it rotates. This simple model explains much of what we can observe on Earth when we use a compass to find North. Yet, despite centuries of study, there are still mysteries about the field. For example, every hiker knows that the magnetic needle usually does not point to the geographic north pole, but to a magnetic north pole that actually moves over the years. Also, the magnetic field has flipped many times in the past, and, the strength of the field varies rapidly through historical and geological times. All these observations suggest that the causes of the magnetic field in the Earth’s core are quite complicated.

Key to understanding these complex processes is to understand, not only the direction of the magnetic field in the geological past, but also its intensity, which is a more difficult experiment. The Scripps Paleomagnetics Lab pioneered novel techniques that can provide reliable intensity data using volcanic rocks that froze particularly fast in the magnetic field at the time of their eruption. This offers new hope that intensity, a key aspect of the magnetic field of Earth, can be reliably determined.

Our expedition to Antarctica capitalizes on this discovery, as well our prior study of the ages and ancient magnetic field directions, for 132 different lava flows that erupted over the last 5 million years in the McMurdo region. Determining paleointensity for the last 5 million years in this volcanic province will help us understand the processes that cause the magnetic field to shift through time.