- Earth formed a molten iron core. Its movement generates electricity, leading to planet-wide magnetic orientation.
- Scientists can track the magnetic history of our planet in cooled lava rocks.
- Since our magnetism deflects the sun’s radiation, it allows life to exist on Earth.
Our planet is one giant magnet, about 8,000 miles across. The magnetic force—an electric interplay between magnetically charged metals in Earth’s core—extends outward into space for thousands of miles. This magnetosphere blocks powerful solar radiation that would otherwise destroy our atmosphere and life on the planet. In fact, solar winds actually blow the magnetic envelope away from Earth in a tail shape.
A fun side-effect of our magnetic protection from the sun is the picturesque Aurora, or Northern and Southern Lights. The dreamy blue-green display results from energized solar particles crashing into our upper atmosphere at speeds of up to 45 million miles per hour. Fortunately, our magnetic field deflects solar wind toward Earth’s poles. Along the way, particles in our ionosphere fluoresce, causing the light show. Astronauts can actually see the aurora from space.
How Did Earth Become Magnified?
Liquified metals like iron in the outer core move around. A lot. Due to Earth’s spin, we have “moving, magnetically chargeable metals,” says astrophysicist Neil deGrasse Tyson in a YouTube short. “When you have moving metal, you create what’s called a dynamo, and in a dynamo, you basically create a magnetic field from scratch. That’s why old, dead planets that have cooled do not have magnetic fields. Mars—no magnetic field to speak of.”
Think of water boiling in a heated pot. It keeps swirling around due to convective forces that move heat through a liquid. In a similar way, Earth’s hot, heavy metal molten core churns, spurred on by planetary rotation. During this constant movement, an electric current, hundreds of miles wide and flowing at thousands of miles per hour, is generated in the heavy metals.
Paleomagneticists who study this phenomenon sample and date rock from Earth’s moving mid-ocean ridges, where tectonic plates take shape from erupting lava that has spread and cooled. The minerals emerging from deep inside Earth are rich in iron, and so they align with the geomagnetic field of the planet, “freezing” the strength and direction of the magnetic field in place by the time the lava cools to about 1,300 degrees Fahrenheit.
This rock sampling has revealed a picture of Earth’s magnetic source from the past 160 million years. Studies show the field is the strongest it’s been over the past 100,000 years, according to NASA.
Don’t Take Magnetic Orientation for Granted
You can easily tell which way the field is pointing by using your compass. However, the magnetic north has been drifting from its familiar position; That’s because where the liquid iron flows influences the location of the two magnetic poles. In fact, the poles have even exchanged positions multiple times over our planet’s history, and the magnetic field strength has waxed and waned. Lately, scientists have noted that a recent shift in the magnetic north pole is happening unusually fast—from nine miles at most each year to as much as 37 miles in a year between 1999 and 2005. This could have implications for any systems that need a compass, like your smartphone, or ships at sea.
Scientists think Earth’s core started solidifying one billion years ago. Yet traditional evidence shows that a magnetic Earth is more than three times older. At this point, it’s generally accepted that geomagnetism began 3.5 billion years ago, but paleomagneticists still aren’t sure how.
What Would Happen if Earth’s Core Solidified?
Just look to Mars. The Red Planet today has no molten core, and its magnetic field drastically diminished about 3.8 billion years ago for reasons unknown. It left the planet—and any life it may have had—open to harmful solar radiation.
For now, we can relax. The dynamo inside our own planet Earth is set to keep roiling for billions of years to come.
Before joining Popular Mechanics, Manasee Wagh worked as a newspaper reporter, a science journalist, a tech writer, and a computer engineer. She’s always looking for ways to combine the three greatest joys in her life: science, travel, and food.