Another cool idea from Israel
Israeli researchers suggest new way of studying Earth’s history – through ice
By ILANIT CHERNICK
Israeli scientists at the Weizmann Institute of Science in Rehovot have suggested a cool new way of reading the Earth’s historic record: in ice.
“The history of our planet has been written, among other things, in the periodic reversal of its [north and south] magnetic poles,” the researchers explained this week.
Their findings “could lead to a refined probing of the ice cores and, in the future, might be applied to understanding the magnetic history of other bodies in our solar system, including Mars and Jupiter’s moon Europa.”
Prof. Oded Aharonson of the Institute’s Earth and Planetary Sciences Department explained that the idea for investigating the possible between ice and the Earth’s magnetic history came about while he was attending a conference on magnetism on the Isle of Corsica.
During the conference, researchers were discussing the field known as paleo-magnetism, “which is mostly studied through flakes magnetic minerals that have been trapped either in rocks or cores drilled through ocean sediments.”
When this happens, such particles then align with the Earth’s magnetic field at the time that they are trapped in place.
“Even millions of years later, researchers can test their magnetic north-south alignment and understand the position of the Earth’s magnetic poles at that distant time,” the scientists explained.
It was this that gave Ahronson his Eureka moment. He concluded that if “small amounts of magnetic materials could be sensed in ocean sediments, maybe they could also be found trapped in ice and measured.
“The Earth’s paleo-magnetic history has been studied from the rocky record,” Aharonson continued. “Reading it in ice cores could reveal additional dimensions, or help assign accurate dates to the other findings in those cores.”
While formulating this theory, he realized that ice frozen in the glaciers in places like Greenland or Alaska is many millennia old and is layered like tree rings.
“Ice cores drilled through these are investigated for signs of planetary warming or ice ages, but why not reversals in the magnetic field as well?” he questioned.
Based on this, Aharonson and his student Yuval Grossman, who led the team, first had to ask “whether it was possible that the process in which ice forms in regions near the poles could contain a detectable record of magnetic pole reversals.
“These randomly-spaced reversals have occurred throughout our planet’s history, fueled by the chaotic motion of the liquid iron dynamo deep in the planet’s core,” the Weizmann Institute explained in a statement. “In banded rock formations and layered sediments, researchers measure the magnetic moment – the magnetic north-south orientations – of the magnetic materials in these to reveal the magnetic moment of the Earth’s magnetic field at that time.
“The scientists thought such magnetic particles could be found in the dust that gets trapped, along with water ice, in glaciers and ice sheets,” it added.
To test this idea, the research team built an experimental setup, which simulated ice formation similar to how it forms in the polar glaciers, “where dust particles in the atmosphere may even provide the nuclei around which snowflakes form.”
Using purified water, the research team created artificial snowfall by finely grinding ice made from purified water, adding a bit of magnetic dust, and letting it fall though a very cold column that was exposed to a magnetic field, the latter having an orientation controlled by the scientists. By maintaining very cold temperatures – around 30 degrees Celsius below zero, they found they could generate miniature “ice cores” in which the snow and dust froze solidly into hard ice.
“If the dust is not affected by an external magnetic field, it will settle in random directions which will cancel each other out,” Aharonson said. “But if a portion of it gets oriented in a particular direction right before the particles freeze in place, the net magnetic moment will be detectable.”
To measure the magnetism of the “ice cores” they had created in the lab, the scientists teamed up with Prof. Ron Shaar’s lab at the Hebrew University in Jerusalem, where a sensitive magnetometer installed there could measure the very slightest of magnetic moments. They found a small, but definitely detectable magnetic moment that matched the magnetic fields applied to their ice samples, which could prove Aharonson’s theory as possible.
The scientists said that it would be exciting to look for magnetic field reversals in ice sampled from other bodies in our solar system
“And we know that the surfaces of Mars and large icy moons like Europa have been exposed to magnetic fields. It would be exciting to look for magnetic field reversals in ice sampled from other bodies in our solar system,” he said, adding: “We’ve proved it is possible,”
Following the findings, Aharonson has proposed a research project for a future space mission involving ice core sampling on Mars, concluding that he hopes that “this demonstration of the feasibility of measuring such a core will advance the appeal of this proposal.”
The findings were recently reported in Earth and Planetary Science Letters.