UNIT-2-EARTH-AS-A-PLANET-Copy-Grade-10.pptx

Grade 10 Science

1. UNIT 2: EARTH AS A PLANET

2. THE INTERNAL STRUCTURE OF EARTH

3. Earth’s Structure The Earth’s structure can be defined mechanically or chemically. Rheology – is a branch of physics that studies the flow of liquid matter and solid material deformation. 3

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5. Compositional Layers of the Earth 5

6. Compositional Layers of the Earth Crust is the outermost layer of Earth. It is the thinnest layer as it makes up only about one percent of Earth. The thickness of this layer is dependent on its age-the thicker the layer, the older the crust. Most earthquakes occur in the crust. 6

7. The Mohorovičić Discontinuity The boundary between the crust and the mantle is known as the Mohorovičić discontinuity popularly known simply as Moho. It was named after the Croatian seismologist Andrija Mohorovičić who discovered its existence in 1909. 7

8. The Mohorovičić Discontinuity He found out that seismic waves abruptly change from a constant difference at a distance greater than 200 km from the epicenter. It was also found that the Moho has an average depth of around 8 km under the ocean basin and around 32 km under the continental crust. 8

9. Compositional Layers of the Earth Mantle the layer of Earth that is composed of iron, aluminum, calcium, magnesium, silicon, and oxygen. About 80% of the planet's mass is concentrated on the mantle and most of the internal heat of Earth is located in this layer including the magma chamber that drives volcanic processes. 9

10. Compositional Layers of the Earth Upper mantle is seen as a highly viscous layer which lies between the crust and the lower mantle. It extends up to 660 km and consists of peridotite and dunite which are solid, ultramafic rocks made up of olivine and pyroxene. 10

11. Compositional Layers of the Earth Lower mantle extends from just under the upper mantle to 2,200 km. Rocks in the upper mantle are cooler and brittle enough to break under stress. On the other hand, rocks at the lower mantle are hot and soft. 11

12. The Gutenberg Discontinuity In 1913, the German-born American seismologist Beno Gutenberg found out that, at some depth, the P-wave slows down and hinders the movement of the S-wave. Gutenberg also expressed that this resulted in the idea that the core is made up of molten materials because it does not allow S-waves to penetrate it. 12

13. Compositional Layers of the Earth The core is the final and innermost layer, which is divided into two parts: the liquid outer core and the solid inner core . The earth's core is the source of the planet's internal heat because it contains radioactive materials that emit heat as they degrade into more stable substances. It is primarily made of an iron-nickel alloy. 13

14. Compositional Layers of the Earth The core is the final and innermost layer, which is divided into two parts: the liquid outer core and the solid inner core . The earth's core is the source of the planet's internal heat because it contains radioactive materials that emit heat as they degrade into more stable substances. It is primarily made of an iron-nickel alloy. 14

15. The Lehmann Discontinuity In the region between the inner and outer core exists a boundary known as the Lehmann discontinuity, named after a Danish seismologist and geophysicist Inge Lehmann. Her discovery is a breakthrough in the study of Earth's interior. Prior to her discovery, seismologists believed that the core was made up of a single molten sphere. 15

16. The Lehmann Discontinuity However, she explained that based on The analysis of seismic wave measurements, the core is made up of a molten region and a solid region. This is based on data showing a sudden increase in the P-wave and S-wave velocities at a depth of 220 km. 16

17. Earth’s Magnetic Field The geomagnetic field protects us from the harmful rays emitted by the sun. Scientists have recorded fluctuations in Earth's magnetic field strength due to intermittent solar flares. This increase in cosmic rays can temporarily affect communication systems, hasten ozone layer depletion, and generate the aurora phenomenon. 17

18. Earth’s Magnetic Field These effects are quite small when compared to much larger magnetic fluctuations known as the geomagnetic flips or geomagnetic reversals. 18

19. Earth’s Magnetic Field During normal polarity, the north magnetic pole is located near Earth's North Pole. A geomagnetic reversal occurs when there is a change in the magnetic field of Earth where the magnetic North Pole shifts to the South Pole Region and the south magnetic pole shifts to the North Pole Region. Once this process is complete, a compass would point toward Antarctica instead of pointing toward northern Canada 19

20. Earth’s Magnetic Field Scientific evidence found in magnetic rocks shows that magnetic reversal has occurred 171 times in the last 71 million years with an average interval of approximately 250,000 years. The north magnetic pole was first located in 1831 and scientists are keeping track of its movement up to the present time. 20

21. Earth’s Magnetic Field Amazingly and alarming at the same time, records show that the pole has moved by 1,100 km and since 1970, it has been moving much faster from 10-40 km annually, which is an incredible pace that requires explanation and research, especially now that Earth is experiencing abnormal geological events. 21