Originally believed to have formed as little as 500 million years ago, the Pluto-sized ball of iron at the center of our planet actually came about between 1.0 and 1.5 billion years ago, researchers from the University of Liverpool’s School of Environmental Sciences have discovered.
The core, which is the Earth’s deepest layer, formed when molten iron in the surrounding outer core solidified. Establishing precisely when it originated has been the topic of spirited debate in the scientific community, and as the authors of the new study explained in a recent edition of the journal Nature, the answer was found in the magnetic records of ancient igneous rocks.
Lead author Dr. Andy Biggin, an expert in paleomagnetism, analyzed those records and found a sharp increase in the strength of the planet’s magnetic field which occurred between 1.0 and 1.5 billion years ago. The researchers believe that this is indicative of the first presence of solid iron at the Earth’s center and the point at which the cooling outer core began to “freeze.”
In a statement, Dr. Biggin admitted that this timeline is “highly controversial” but said that it was “crucial for determining the properties and history of the Earth’s interior” and added that it “has strong implications for how the Earth’s magnetic field – which acts as a shield against harmful radiation from the sun, as well as a useful navigational aid – is generated.
“The results suggest that the Earth’s core is cooling down less quickly than previously thought which has implications for the whole of Earth Sciences, the Liverpool researcher added. “It also suggests an average growth rate of the solid inner core of approximately 1mm per year which affects our understanding of the Earth’s magnetic field.”
Explaining why Earth has life and Mars doesn’t
According to Live Science and Discovery News, the original rocky fragments of Earth began to merge a little over 4.5 billion years ago, and for much of its early life, the planet was just a mass of molten rock. Eventually, however, the surface cooled and formed a crust which floated on top of its liquid core, ultimately developing an atmosphere and biological life.
Somewhere in the midst of all this, the molten iron found deep within the planet solidified, but experts have long debated exactly when this process would have taken place. Some argue that it occurred just 500 million years ago, while other believe that the inner core formed roughly 2.0 billion years ago. This new research appears to narrow the timeframe down somewhat.
“The theoretical model which best fits our data indicates that the core is losing heat more slowly than at any point in the last 4.5 billion years and that this flow of energy should keep the Earth’s magnetic field going for another billion years or more, said Dr. Biggin.
“This contrasts sharply with Mars which had a strong magnetic field early in its history which then appears to have died after half a billion years,” he added. The lack of protection from solar radiation could help to explain why Earth is home to a wide variety of living organisms while the Red Planet appears to be devoid of life.
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Feature Image: Kay Lancaster, Department of Earth, Ocean and Ecological Sciences
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