ICE RECORDS MAGNETIC HISTORY

July 17, 2020

Earth’s magnetic history has been studied from various elements and this time Scientists from Weizmann Institute of Science have proposed ice to be one such element. Yes, you have read it right, it’s ICE !!! But of course, not a random cube of ice but naturally occurring ice (Example - Polar Glaciers).

 Professor Oded Aharonson of the Weizmann Institute’s Earth and Planetary Sciences Department was attending a conference on Paleomagnetism, which is mostly studied through flakes magnetic minerals that have been either trapped in rocks or cores drilled through ocean sediments. Such particles get aligned with Earth’s magnetic field at the time of getting trapped, and even after millions of years later, researchers can test their magnetic north-south alignment and test the position of Earth’s magnetic poles at that distant time. The latter part gave Aharonson the idea that if a small number of magnetic minerals can be trapped in oceanic sediments, then they might even be found trapped in ice and be measured.

       Randomly-spaced magnetic pole reversals have occurred throughout our planet’s history, fuelled by the chaotic motion of the liquid iron dynamo deep in the planet's core. In banded rock formations and layered sediments, researchers measure the magnetic moment of magnetic materials in order to reveal the magnetic moment of the Earth’s field at that time. Aharonson and his student Yuval Grossman thought such magnetic particles could be found in dust trapped along with water ice, glaciers, and ice sheets. The research team built up an experimental set up to simulate ice formation similar to polar glaciers, where dust particles in the atmosphere may even provide the nuclei around which snowflakes form. Artificial snowfall was created by finely grinding ice made from purified water, adding a bit of magnetic dust, and letting it fall through a magnetic column that was exposed to a magnetic field controlled by the scientists. By maintaining a very cold temperature (around -30 °C), they could successfully generate miniature “ice cores” in which the snow and dust froze solidly into hard ice. To measure the magnetism of these ice cores Professor Ron Shaar’s lab at Hebrew University in Jerusalem was used where a sensitive magnetometer was installed which could measure the slightest of magnetic moments.

 

Next to Prof Aharonson is the triaxial Helmholtz Coil used to generate the magnetic field during the growth of ice samples. CREDIT: Weizmann Institute of Science.
Detection of net magnetic moment means a portion of the magnetic particles got oriented in a particular direction and zero magnetic moment signifies that the dust is not affected by any external magnetic field and hence it has randomly settled down to cancel out each other. The team found small but detectable magnetic moments that matched the magnetic field reversals in ice sampled from other bodies in the solar system.
      This experiment proved that Earth’s paleomagnetic history can be studied from the ice core sampling on Planet Earth.

SOURCES
1.    https://www.sciencedaily.com/releases/2020/06/200629120238.htm
2.    https://doi.org/10.1016/j.epsl.2020.116408
3. https://www.researchgate.net/publication/342449548_Experimental_determination_pf_remanent_magnetism_of_dust_ice_deposits

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