Discovery of Oldest evidence of Earth’s Magnetic field

Context

Ancient rocks that bear the oldest remnants of Earth’s early magnetic field were discovered in Greenland by the geologists at MIT and Oxford University.

Oldest evidence of Earth’s magnetic field in Greenland rocks

• Study published in: The Journal of Geophysical Research.
• Sample for the study: Rock formations in the Isua Supracrustal Belt in southwestern Greenland were sampled for the study.
  • The rock samples were of banded iron formations ie. a rock type that appears as stripes of iron-rich and silica-rich rock.
• Objective: To  find rocks that still held signatures of the Earth’s magnetic field when they were  first formed.
• Process used: Through the process of Remagnetisation, the researchers used uranium to lead ratio and found that some of the magnetized minerals were likely about 3.7 billion years old.
• Findings: 
  • The rocks are determined to be about 3.7 billion years old and they retain signatures of a magnetic field with a strength of at least 15 microtesla.
    • Today, Earth’s magnetic field measures around 30 microtesla. 
  • Origin of the rock: The rocks could have been originally formed in primordial oceans prior to the rise in atmospheric oxygen around 2.5 billion years ago, given their composition.

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• Significance: 
  • The discovery extends  the magnetic field’s lifetime by another 200 million years with the rocks  representing some of the earliest evidence of a magnetic field surrounding the Earth.
    • Previous studies have shown evidence for a magnetic field on Earth that is at least 3.5 billion years old.
  • Early evidence on the habitable nature of Earth: The discovery sheds light on how the Earth was able to foster life early in its evolution ie.  in part due to an early magnetic field that was strong enough to retain a life-sustaining atmosphere and simultaneously shield the planet from damaging solar radiation. 

What is Earth’s magnetic field?

• It is also known as the geomagnetic field, is generated in the interior of the planet  and extends out into space, creating a region known as the magnetosphere.  
• First discovered: British polar explorer James Clark Ross first identified the Magnetic North Pole on the Boothis Peninsula in Canada’s Nunavut territory in 1831.
• Location: Magnetic poles are located where the magnetic lines of attraction enter Earth. The Magnetic North Pole is also known as the North Dip Pole and is currently located on Ellesmere Island in Northern Canada.
  • The Magnetic North Pole is about 310 miles (500 kilometers) away from the Geographic North Pole.
• Features: 
  • Dipolar:  Magnetic field sources are dipolar, i.e. they have a north and south pole. In  magnets, opposite poles (N and S) attract while other poles (N and N, S and S) repel.
    • Therefore, the North Magnetic Pole which  lies close to the Geographic North Pole in essence is  a south magnetic pole.
  • Not fixed: Earth’s magnetic poles are not fixed and tend to wander over time. The  magnetic north pole has been moving  about 25 miles (40 kilometers) a year in a northwest direction since it was first identified, according to the Royal Museums Greenwich.
  • Magnetic Reversals:  Earth’s magnetic poles have also flipped whereby north becomes south and south becomes north. The phenomenon  occurs at irregular intervals every 200,000 years or so.
    • Earth’s most recent magnetic reversal occurred approximately 790,000 years ago.
  • Auroras: It is a feature of magnetosphere disturbances witnessed above Earth’s polar regions. 
    • The disturbances in Earth’s magnetic field funnel ions down towards Earth’s poles where they collide with atoms of oxygen and nitrogen in Earth’s atmosphere, creating dazzling aurora light shows. 
    • The phenomenon is known as the northern lights (aurora borealis) in the Northern Hemisphere and the southern lights (aurora australis) in the Southern Hemisphere. 

What causes Earth’s magnetic field?

The Magnetic Field is generated through a process named the geodynamo process. It has  the following characteristics:

• The planet should  rotate  fast enough
• The planets interior must have a fluid medium  
• The interior fluid must have the ability to conduct electricity 
• The core must have an internal source of energy that propels convection currents in the liquid interior. 

Process: 

• Earth’s magnetic field is generated in a layer known as the outer core, deep inside Earth’s Interior.
• Conversion of Energy: Here the convective energy from the slow-moving molten iron is converted to electrical and magnetic energy. 
• Feedback Loop: The magnetic field then induces electric currents which in turn generate their own magnetic field which induces more electric currents, in a positive feedback loop.

Importance:  

• Protected Atmospheric Layer: The magnetosphere protects us from harmful space weather such as solar wind without which, the solar wind would have eroded our atmosphere, devoiding our planet of the life-giving air we breathe. 
• Harmful Radiation: The magnetosphere protects Earth from the effect of particle radiation emitted during coronal mass ejection (CME) events and also from cosmic rays (atom fragments raining down on Earth from deep space).
• Van-allen belts: The magnetosphere repels harmful energy away from Earth and traps it in zones called the Van Allen radiation belts. These donut-shaped belts of radiation can swell when the sun’s activity increases. 
  • It  is a zone of energetic charged particles that are captured by and held around a planet by that planet’s magnetosphere. 
  • Earth has two such belts, and sometimes others may be temporarily created. 

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