Describe the sources which provide the information about the Earth’s interior. How does the study of seismic waves help us understand the layered structure of the earth? [200 words]
The interior of the earth can be understood by indirect evidences as it is not possible to reach the interior of the earth.
Direct Sources
- Deep earth mining and drilling reveals the nature of rocks deep down the surface. [Mponeng gold mine and TauTona gold mine in South Africa are deepest mines reaching to a depth of 3.9 km. And the deepest drilling at Kola, arctic ocean is about 12 km deep]
- Volcanic eruption forms another source of obtaining direct information.
Indirect Sources
- Depth: With depth, pressure and density increases and hence temperature. This is mainly due to gravitation.
- Meteors: Meteors and Earth are solar system objects that are born from the same nebular cloud. Thus they are likely to have a similar internal structure.
- Gravitation: The gravitation force is not the same at different latitudes on the surface. It is greater near the poles and less at the equator because of its greater distance at the equator that at the poles, from the centre of the earth.
- Gravity anomalies (uneven distribution of mass within the earth) give us information about the distribution of mass of the material in the crust of the earth.
- Magnetic field: The geo-dynamo effect helps scientists understand what’s happening inside the Earth’s core. Shifts in the magnetic field also provide clues to the inaccessible iron core.
Behaviours of Seismic Waves
- The real concrete proof about the interior of the earth was provided by the study of seismic waves.
- The behaviour of seismic waves upon traversing deep into the earth provides the most authentic evidence about the composition & layered-structure of the earth. The different types of waves generated during the occurrence of earthquake, are generally divided into 3 broad categories;
(a) Primary (P) waves, (b) Secondary (S) waves, (c) surface waves.
- Seismic Waves- both P-waves & S-waves travel faster through rigid material than through soft or plastic material. The velocities of these waves travelling through specific part of earth gives an indication of type of rocks there. Abrupt changes in seismic wave velocities indicate significant changes in earth’s interior.
- Seismic waves passing through the earth are refracted in ways that show distinct discontinuities within earth’s interior & provide basis for the belief that earth has
(1) a solid inner core, (2) a liquid outer core, (3) a soft asthenosphere, (4) a rigid lithosphere.
PRELIMS (STATIC)
- The annual range of temperature in the interior of the continents is high as compared to coastal areas. What is/are the reason/reasons? [CSE (PRE)-2013]
- Thermal difference between land and water.
- Variation in altitude between continents and oceans.
- Presence of strong winds in the interior.
- Heavy rains in the interior as compared to coasts.
(a) 1 only
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1, 2, 3 and 4
Solution: (a)
DAILY CURRENT AFFAIRS
- Which of the following statement(s) is/are correct about the National e-Vidhan Application?
- It is under the ambit of the Ministry of Parliamentary Affairs.
- It aims to make all the Legislatures of the country paperless by making the proceedings of the Houses digital.
a. 1 only
b. 2 only
c. Both 1 & 2
d. None of the above
Solution: (c)
Source: http://pib.nic.in/newsite/PrintRelease.aspx?relid=183679
2.Which of the following statement(s) is/are true about the newly set-up Centre of Excellence for Data Analytics?
- It will improve the overall governance by unlocking the hidden potential of the data, generated as part of governances processes.
- It aims at providing quality data analytic services to government departments at all levels by identifying appropriate tools and technologies and deploying people with right expertise.
- It is under the ambit of the Ministry of Communications.
a. 1 & 2
b. 2 & 3
c. 1 & 3
d. 1, 2 & 3
Solution: (a)
Source: http://pib.nic.in/newsite/PrintRelease.aspx?relid=183759
Prepared By: Bikesh Varman