More than 5,100 km deep beneath our feet lies the Earth’s inner core, a solid sphere of iron and nickel that plays a vital role in shaping the surface environment – in fact, without the inner core we probably wouldn’t even exist.
But despite its importance, how it formed and developed is a bit of a mystery. We don’t even know how old it is. Luckily, mineral physics is bringing us closer to solving the mystery.
The inner core controls Earth’s magnetic field, which acts like a shield to protect us from harmful solar radiation and may have been important in creating an environment in which life could thrive billions of years ago.
The Earth’s inner core was once liquid but over time it turned solid.
As the Earth gradually cools, the inner core expands outward and the surrounding iron-rich liquid “freezes,” although it is still very hot. At least 5,000 Kelvin (K) (4726.85°C).
This freezing process releases elements such as oxygen and carbon that cannot exist in a hot solid, which creates a hot, buoyant liquid at the bottom of the outer core.
The liquid rises into the liquid outer core and mixes, generating electric currents (due to “dynamo action”) and creating a magnetic field.
Have you ever wondered why the Aurora Borealis keeps dancing in the sky? It’s thanks to the inner core.
Mysterious Crystallization
Geophysicists use models that simulate the thermal conditions of the core and mantle to understand how Earth’s magnetic field has evolved throughout its history.
These models help us understand how heat is distributed and transferred inside the Earth. These models postulate that a solid inner core first appeared when the liquid cooled to its melting point, which dates this to the birth time of the Earth’s core. When it starts to freezeThe problem is that it doesn’t reflect that accurately. The freezing process.
Scientists have therefore been studying the process of “supercooling,” which occurs when a liquid is cooled below its freezing point without becoming a solid. Water in the atmosphereTemperatures can reach -30°C before hail forms and it has also been linked to iron in the Earth’s core.
Calculations suggest that in practice supercooling to 1,000 K may be necessary. Freeze pure iron It is located in the Earth’s core, which poses a big challenge since the core’s conductivity means it is expected to cool at a rate of 100-200K per billion years.
This level of supercooling means that the core has been below its melting point for its entire history (between 1 billion and 500 million years), introducing an additional complication.
Humans have only been able to drill down to 12km into the Earth because they do not have physical access to the center of the Earth. We rely almost entirely on seismology. To understand the interior of the Earth.
The inner core was discovered in 1936, and its size (about 20% of the Earth’s radius) is one of the best known features of the deep Earth. We use this information to estimate the temperature of the core, assuming that the solid/liquid boundary represents the intersection of the melting point and the core temperature.
This assumption also helps estimate the maximum extent of supercooling that could have occurred before the inner and outer cores combined and began to form the inner core.
If the core froze relatively recently, the current thermal conditions at the boundary between the inner and outer cores indicate how much colder the bound core was below its melting point when the inner core first began to freeze. This means that the core must have been at most Approximately 400K supercooling.
This is at least twice what seismology allows: if the core had been supercooled by 1,000K before freezing, the inner core would have been much larger than observed, whereas freezing requires 1,000K, and if that was never achieved, the inner core would not have existed in the first place.
Clearly, neither scenario is accurate. So what’s the explanation?
Mineral physicists have been testing pure iron and other mixtures to see how much supercooling is needed to start forming the inner core, and while these studies have not yet produced a conclusive answer, there has been promising progress.
For example, we Crystal structure and Presence of carbon These findings suggest that certain chemical reactions or structures not previously considered may not require unreasonably large supercooling.
If the core could be frozen at a supercooling temperature below 400K, this could explain the existence of the inner core we see today.
The implications of not understanding the formation of the inner core are far-reaching. Previous estimates of the inner core’s age are range 500 million to 1 billion years. But this doesn’t take into account the problem of supercooling: even a modest supercooling of 100,000 degrees could mean that the inner core is hundreds of millions of years younger than previously thought.
Understanding the signature of inner core formation in the paleomagnetic rock record, which is a record of the Earth’s magnetic field, is crucial for those studying the effect of solar radiation on mass extinctions.
Until we have a better understanding of the history of the magnetic field, we won’t be able to fully pinpoint its role in the emergence of habitable environments and life.
Alfred Wilson SpencerMineral Physics Researcher, University of Leeds
This article is reprinted from conversation Published under a Creative Commons license. Original article.
