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  • You know, weve managed to go hundreds of thousands of miles into space, but when it

  • comes to the earth, weve barely scratched the surface. Our planet’s core is a magnificent

  • mystery filled with secrets. It’s time to figure them out.

  • The Earth’s inner core is an extra hot solid ball with an approximate radius of 760 miles.

  • To put that into perspective, it’s just 30% smaller than the moon. But if weve

  • never been there, how did we find this out? Well, weve learned about the core by observing

  • the effects of gravity on objects on the surface of our planet. From there, it’s estimated

  • that the Earth’s mass is 5.6 sextillion tons. Get out your bathroom scaleno don’t.

  • The density of everything that lies on the surface is much lower than the core’s average

  • density. Scientists figured out that most of the Earth’s mass is located towards the

  • center of our planet. It’s estimated that more than 80% of the

  • core consists of one of the ten most common elements in our galaxy: iron. But, the iron

  • on the Earth’s surface is kind of limited. I know what youre wondering, “How did

  • the iron make it all the way down to the core?” Well, there’s a simple explanation.

  • The heavy element somehow pushed itselfliterallytowards the center of the Earth, and a

  • ton (pardon the pun) of research was done to figure out how. Most of the Earth’s surface

  • is made of rocks called silicates, and the molten iron had some difficulty passing through

  • them. To help you understand, think of how water struggles to get through a greasy surface.

  • But in 2013, Wendy Mao and her team from Stanford discovered a possible solution for how this

  • happened. They began an experiment to see how iron and silicate react when theyre

  • exposed to extreme pressurelike that in the core.

  • They used a diamond anvil cell to pinch the two substances under those conditions and

  • they achieved it. The pressure was 330 gigapascals, which is around 3.3 million times the atmospheric

  • pressure of our planet. The molten iron slowly squeezed through the silicate rocks, and they

  • had their answer. It took millions of years for the iron to reach the center, so it happened

  • at a snail’s pace. Since snails weren’t around back then, the iron had to guess how

  • fast to go. Well, now that we got that figured out, how

  • do we know what size the core is? That’s when seismology comes into play. During an

  • earthquake, shockwaves are spread through the planet. Seismologists study these vibrations

  • and try to read the reflections on the other side. It’s like Thor is hitting one side

  • of the planet with his hammer, and the seismologists are listening from the opposite end.

  • But these vibrations also take different routes. They go through various parts of the planet,

  • and that affects the sound they make at the end. Let’s take a small detour for a minute.

  • Seismology is quite an old scientific field. In the old days, when vibrations occurred,

  • scientists noticed that something was wrong with them. These vibrations were “S-Waves”,

  • and when they were supposed to show up on the other side, they just vanished.

  • At first, they thought that something was wrong with their equipment, and it just wasn’t

  • picking up the vibrations. But as science progressed, it turned out that these picky

  • “S-WAVEScould only go through solid material, and not liquid.

  • So something molten was present in the center of the Earth that was preventing the vibrations

  • from going through. So, they started digging into their data. They mapped out the paths

  • of the seismic waves and found that around 1,860 miles from the Earth’s surface, the

  • rocks transformed into a liquid. But there’s also an interesting fact in

  • the game. Inge Lehmann was a Danish seismologist (see,

  • there’s my Shakespeare tie-in), and in the 1930’s she discovered a new wave pattern.

  • First, we had the S-Waves that didn’t pass through liquid, but then there were also P-waves

  • that could travel through the core and appear on the opposite side of the planet. That was

  • when Inge came up with the theory that the core has two layers. The solid inner core,

  • which is around 3700 miles below the surface, and the molten outer core, which is around

  • 1860 miles below our feet. When advanced seismographs were invented, her theory was confirmed, but

  • that took 40 years. So, now that we also have the structure figured

  • out, let’s talk about how hot the core is and why. Weve already established that

  • we can’t put a thermometer down there to study the temperatures. So, scientists tried

  • to figure that out by creating the same crushing pressures in their labs.

  • Again, in 2013, a team of French researchers came up with the most accurate number that

  • weve had in years. They put pure iron through high pressurealmost higher than that

  • of the core, to come up with their findings: The temperature of the inner core is about

  • 9800°F. While the melting point of pure iron is about 2,800°F, at the core, its melting

  • point is around 11,000° F. The fluctuation in those temperatures comes from factoring

  • in the extreme pressure the iron is exposed to at the core.

  • Also, other elements inside the core could be bringing the temperature down by approximately

  • 400° F. But the reason it remains solid is because

  • of the slow cooling of the outer core and its compression. The inner core spins faster

  • than the Earth. That’s caused by the thermal activity inside our planet which creates the

  • magnetosphere. Oddly, it takes a ton of time for heat to leave the Earth. But I’ll get

  • into that in a bit. There are three main reasons why the earth

  • is still boiling. The first one is that the core has remained hot from the time our planet

  • was formedroughly 4.5 billion years ago. Remember that number, because towards the

  • end I’ll explain how that happened. That heat hasn’t been lost yet. In fact, the

  • earth is only cooling down around 200°F every billion years.

  • Secondly, it generates heat from the friction of the dense materials as they move.

  • And the last reason it’s so hot is from the decay of radioactive elements. So, why

  • is this important? It makes it easy for scientists to understand how it affects the speed of

  • vibrations that go through the core. Remember the “P-Waves” I told you about

  • earlier? Well, these guys travel slower than they should while passing through the core.

  • This shows that there must be some other element in there that we haven’t figured out yet.

  • Nickel is one of them, but when scientists ran some tests with nickel, the P-waves didn’t

  • slow down enough. So, they started diggingmetaphorically.

  • In 2015, a new study from Durham University came out. It claimed that 90% of the Earth’s

  • sulfur is in the core. So, maybe that could be the missing element. Around 4.5 billion

  • years ago, the Earth collided with a large planetary body that eventually tore apart

  • our planet and formed the moon. That incident left traces behind that led the studies in

  • a new direction. When the impact happened, the Earth’s mantle

  • melted, and some sulfur-rich liquid squeezed through the ruins and reformed it. Some of

  • it was probably lost in space, but the rest sunk to the core.

  • Scientists from Durham University confirmed that theory by measuring the isotope ratios

  • of elements in the mantle. They compared them to meteorites, which were possibly part of

  • the Earth’s original form. The problem was that there are so many different elements

  • in the mantle, it’s quite difficult to draw firm conclusions. So, they came up with another

  • idea. Copper is usually bound to sulfur. So, they

  • analyzed the copper from the Earth’s mantle and crust. Now, this was a 3-stage study done

  • in different labs, using state-of-the-art mass spectroscopes. Ya still with me here?

  • Good for you! They found that there was a teeny tiny difference in the copper ratios

  • between the Earth’s mantle samples and the meteorite samples. That confirmed the theory

  • that the Earth originally collided with another body, and most of its mantle just splattered

  • around space. We also know that the core consists of some sulfur.

  • Hopefully soon, well be able to find out what the other trace elements are.

  • So to answer your final question, yes, the center of the earth ishard-core! Yeah,

  • you were waiting for that one, weren’t you? Hey, if you learned something new today, then

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You know, weve managed to go hundreds of thousands of miles into space, but when it

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B1 BRIGHTSIDE core earth iron planet mantle

Why the Earth's Core Is Hotter Than the Sun

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    林宜悉 posted on 2020/03/12
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