Alec Brenner, Ph.D.

I apply paleomagnetic and petrographic methods to the oldest rocks, especially those dating back to the Archean Eon (~4 to 2.5 billion years ago or Ga), to study many aspects of the early Earth:

• Unraveling the complexity of magnetizations in hydrothermally-altered rocks. Almost all Archean rocks have experienced some degree of hydrothermal alteration, complicating interpretations of paleomagnetic data. Using a mix of cutting-edge magnetic microscopy techniques and old-school petrography, I study how seafloor hydrothermal systems remagnetize the rocks that host them at microscopic to regional scale.
• The much-debated role of plate tectonics in deep time. Plate tectonics exerts major influences on nearly every process on the modern Earth, but how and when did this “mobile-lid” mode of geodynamics first manifest? By measuring the paleomagnetic record of rocks as old as 3.5 Ga, I track the paleogeography and surface motions of the crustal blocks on which they formed, thus showing whether they were experiencing plate tectonic motions.
• The early geodynamo. Just like the dynamics of Earth’s surface, the inner workings of the geodynamo are uncertain in deep time: since the inner core likely had not crystallized yet, what was the energy source driving the early dynamo? I use paleomagnetic data from early rocks to directly probe the dynamo by measuring its time-variability and reversal history.

Thus far, my research in these areas has led to several significant discoveries, including:

• The oldest documented plate-like lithospheric surface motions by 3.3 Ga.
• The oldest documented dipolar geomagnetic reversal at 3.25 Ga.
• Archean seafloor hydrothermal systems that preserved datable remanences in their footwalls. This demonstrated that a vast suite of previously-unstudied hydrothermally-altered rocks worldwide likely contain paleomagnetically-accessible Archean remanences.