The report, published in the Journal of Geophysical Research by geologists from the Massachusetts Institute of Technology and Oxford University, reveals insights into Earth’s ancient magnetic field as revealed by ancient rocks, shedding light on its early geological evolution.
Key findings of the report
Magnetic field strength
- Geologists have discovered ancient rocks about 3.7 billion years old in the Isua supracrustal belt in southwestern Greenland, which contain the oldest remnants of Earth’s early magnetic field.
- The rocks remained intact as a result of a magnetic field with a strength of at least 15 microtesla, which is similar in magnitude to Earth’s magnetic field today (about 30 microtesla).
Lifetime of magnetic field
- Previous studies had shown that the magnetic field on Earth is at least 3.5 billion years old, but this study extends its lifetime by another 200 million years.
- Using uranium to lead ratio analysis, the researchers estimated that some of the magnetic minerals in the rocks were about 3.7 billion years old.
Potential role in Earth’s habitability
- The ancient magnetic field may have played an important role in making the planet habitable.
- This probably helped maintain a life-sustaining atmosphere and protected the planet from harmful solar radiation.
Uranium-to-lead ratio analysis
- Uranium-lead dating, or U-Pb dating, is a radiometric dating technique that uses the ratio of uranium isotopes to lead isotopes to determine the age of Earth materials.
- The ratio of uranium to lead is used to determine the rate at which uranium decomposes into lead, which is used to determine the age of the rock.
Earth’s magnetic field
- Earth’s magnetic field, also known as the geomagnetic field, originates in the planet’s interior and extends into space, forming a region called the magnetosphere and interacting with the solar wind.
- The magnetic field is generated by convection currents of molten iron and nickel in the Earth’s core, which carry charged particles and generate the magnetic field.
- Not only Earth, but other planets such as Jupiter, Saturn, Uranus and Neptune also have strong magnetic fields, which are not yet fully understood.
- Mars lacks the internal heat and fluid needed to have a magnetic field, while Venus has a liquid core but rotates too slowly to generate liquid.
Geodynamo process
- Earth’s magnetic field is generated by geodynamo processes in the outer core.
- Convection energy from the slowly moving molten iron in the outer core is converted into electrical and magnetic energy, creating a positive feedback loop.
Magnetic pole
- Earth has two groups of poles: geographic poles and magnetic poles.
- The Geographic North and South Pole are the places where longitude lines meet, the Geographic North Pole is located in the middle of the Arctic Ocean and the Geographic South Pole is located in Antarctica.
- In contrast, the magnetic poles are the places where magnetic field lines enter and exit the Earth’s surface.
- The magnetic north pole, also known as the North Dip Pole, is currently found on Ellesmere Island in northern Canada.
- When a compass points north, it is aligning itself with the Earth’s magnetic field and pointing toward the magnetic north pole, not the true geographic north pole.
Space weather protection
- Earth’s magnetosphere protects the planet from harmful space weather, such as solar winds, coronal mass ejections (CMEs), and cosmic rays.
- The magnetosphere repels harmful energy away from Earth and traps it in regions called the Van Allen radiation belts.
Geomagnetic storms and auroras
- During strong space weather events, Earth’s magnetic field can be disrupted, causing geomagnetic storms that can cause power outages (blackouts) and communications disruptions.
- Disturbances in the Earth’s magnetic field also send ions toward the polar regions, causing the formation of auroras (Northern Lights and Southern Lights).