पथ्वी की आतरिक संरचना की जानकारी प्राप्त करने के लिए उपलब्ध अप्रत्यक्ष स्रोतों का वर्णन करें। उनमें सबसे अधिक
महत्त्वपूर्ण कौन है और क्यों?
Describe the indirect sources for the study of the internal structure of the earth. Which of them is the most
important and why?
3. पृथ्वी के मैटल (भूप्रावार) और क्रोड का वर्णन करें।
Describe the mantle and core of the earth.
4. पृथ्वी के आंतरिक भाग की जानकारी प्राप्त करने में भूकंपी तरंगों के अध्ययन ने किस तरह सहायता पहुँचाई है?
How have the studies of seismic waves helped to know about the interior parts of the earth?
Answers
(1)
- By analyzing the rate of change of temperature and pressure from the surface towards the interior.
- Meteors, as they belong to the same type of materials earth is made of.
- Gravitation, which is greater near poles and less at the equator.
- Gravity anomaly, which is the change in gravity value according to the mass of material, gives us information about the materials in the earth’s interior.
- Magnetic sources.
- Seismic Waves: the shadow zones of body waves (Primary and secondary waves) give us information about the state of materials in the interior.
The Mantle
Sitting on top of the outer core, we find the mantle. This layer is by far the thickest layer of Earth, about 1,800 miles thick! It also makes up about 85% of Earth's volume. Like the core, the mantle contains mostly iron, but in the form of silicate rocks. You might be surprised to learn that this rock actually moves like a fluid, similar to how silly putty moves. If you poke silly putty hard, it acts like a solid, but if you slowly pull it apart, it acts like a liquid. We call this ability of rock to move without breaking plasticity.
The mantle can also be divided into two portions, the upper mantle and the lower mantle. The lower mantle is completely solid because, like the solid inner core of Earth, the pressure is just too great for it to melt and flow. The upper mantle is also known as the asthenosphere, which flows as convection currents. Convection occurs in all fluids and is the rising of warm particles and sinking of cool particles. So, as the material in the upper mantle warms, it rises straight up, and as it rises, it cools and then sinks back down.
Earth's Core
You may have heard that ogres are like onions because they have many layers. Well, Earth is the same way! Earth is made up of several different layers, each of which has unique properties.
Let's start from the inside and work our way out. Earth has a core, but this is really two distinct parts: the inner core and the outer core. Both parts of the core are made up of mostly iron and some nickel. The difference is that in the inner core, those minerals are solid and in the outer core, they're liquid.
The inner core of the earth is incredibly hot - so hot that if you tried to dig a hole to China, you'd burn up on your way through the earth! What's amazing about the inner core is that even though it's about as hot as the surface of the sun, there's so much pressure from the weight of the world pushing down on it that it can't melt. This is the same reason that water in a pressure cooker doesn't boil, no matter how hot it gets!
The outer core is also made up of iron and nickel, but it's quite different because it is a liquid. This is because there is much less pressure on this layer than the one below it (the outer core adds a lot of pressure to the inner core!). Though the flow of this liquid layer is very slow-moving (about a few kilometers a year), it is what produces Earth's magnetic field. Our North and South Poles exist because of this liquid outer core, even though it's almost 2,000 miles below us.
4)
Waves transfer energy from source to detector. They also tend to reflect at sudden changes in density. Waves that travel outwards (in 3D) from the epicentre of an earthquake (or more precisely the focus, as the epicentre is the point on the *surface * where waves first appear) can be reflected when they hit the interface between crust and mantle as they travel downwards, so return towards the surface and are detected there.
Longitudinal waves (primary, or p-waves) are able to travel through both liquids and solids, so can move down through both crust and mantle and through the outer core. The transverse or secondary (s-waves) are not able to do so. This means that on the opposite side of the earth to the focus, there will be a region of the earth where no s-waves are detected, the size of the "s-wave shadow" gives the size of the outer, liquid, core.
The inner core is again solid, but the sudden change in density causes some p-wave reflection towards the surface again, meaning its size can be estimated.