Scientists propose age of Earth’s magnetic field
16 Jun 2016 by qmtbqdmdjq.d qmtbqdmdjq.d
The Earth’s magnetic field has existed for at least 3.4 billion years, in part due to the low heat conduction of iron in its core, claim researchers.
The Earth’s magnetic field has existed for at least 3.4 billion years, in part due to the low heat conduction of iron in its core, claim researchers.
Scientists at the Deutsches Elektronen-Synchrotron (DESY) have for the first time measured the core’s thermal conductivity. The Earth’s magnetic field is created by the ‘stirring’ of the iron-rich outer core of the planet combined with the Earth’s rotation.
Zuzana Konôpková, first author from DESY, said: “We measured the thermal conductivity of iron because we wanted to know what the energy budget of the core is to drive the dynamo. Generation and maintenance of our planet's magnetic field strongly depend on the thermal dynamics of the core."
Researchers used a specifically designed pressure cell that compressed samples between diamond anvils, before heating them with infrared lasers. By compressing iron samples at different temperatures and pressures, the scientists found low values of thermal conductivity, between 18 to 14 Watts per metre per Kelvin.
Numerical models have suggested that a high thermal conductivity means the Earth’s magnetic field would have existed for around one billion years. Recently calculations suggest a high thermal conductivity of 150W per metre per Kelvin, but being this high, there is a lower chance of the geodynamo starting up. But researchers have been able to trace it back at least 3.4 billion years creating a paradox.
Konôpková said: “There's been a fierce debate among geophysicists because with such a large thermal conductivity, it becomes hard to explain the history of the geomagnetic field which is recorded in ancient rocks.”
The research was published in Nature.
