{"id":386,"date":"2019-06-11T14:50:19","date_gmt":"2019-06-11T14:50:19","guid":{"rendered":"https:\/\/opentextbc.ca\/physicalgeology2ed\/part\/chapter-9-earths-interior\/"},"modified":"2021-12-08T00:27:09","modified_gmt":"2021-12-08T00:27:09","slug":"chapter-9-earths-interior","status":"publish","type":"part","link":"https:\/\/opentextbc.ca\/physicalgeology2ed\/part\/chapter-9-earths-interior\/","title":{"raw":"Chapter 9 Earth\u2019s Interior","rendered":"Chapter 9 Earth\u2019s Interior"},"content":{"raw":"<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\">Learning Objectives<\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n\r\nAfter carefully reading this chapter, completing the exercises within it, and answering the questions at the end, you should be able to:\r\n<ul>\r\n \t<li>Explain the variations in the composition and characteristics of Earth\u2019s different layers.<\/li>\r\n \t<li>Compare the characteristics and behaviour of the two types of seismic body waves.<\/li>\r\n \t<li>Summarize the variations in seismic-wave velocity as a function of rock type and temperature and pressure conditions.<\/li>\r\n \t<li>Explain some of the ways that seismic data can be used to understand planetary interiors.<\/li>\r\n \t<li>Describe the temperature variations within Earth and their implications for internal processes such as mantle convection.<\/li>\r\n \t<li>Explain the origins of Earth\u2019s magnetic field and the timing of magnetic field reversals.<\/li>\r\n \t<li>Describe the isostatic relationship between the crust and the mantle, and the implications of that relationship for geological processes on Earth.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\nIn order to understand how Earth works, and especially the mechanisms of plate tectonics (covered in Chapter 10), we need to know something about the inside of our planet \u2014 what it\u2019s made of, and what goes on in there. We have a variety of ways of knowing, and these will be discussed in this chapter, but the one thing we can\u2019t do is go down and look! Fortunately there are a few places where mantle rock is exposed on Earth\u2019s surface, and we have some samples of material from the insides of other planetary bodies, in the form of meteorites that have landed on Earth (Figure 9.0.1). We also have a great deal of seismic information that can help us understand the nature of Earth\u2019s interior.\r\n\r\n[caption id=\"attachment_384\" align=\"aligncenter\" width=\"900\"]<a href=\"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/06\/meteorites.png\"><img class=\"wp-image-384\" src=\"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/06\/meteorites.png\" alt=\"\" width=\"900\" height=\"277\" \/><\/a> Figure 9.0.1 Left: a fragment of the Tagish Lake meteorite, discovered in 2000 on the ice of Tagish Lake, B.C. It is a \u201cstony\u201d meteorite that is dominated by ferromagnesian silicate minerals, and is similar in composition to Earth\u2019s mantle. Right: part of the Elbogen meteorite discovered in Germany around 1400. It is an iron meteorite, similar in composition to Earth\u2019s core. Both samples are a few centimetres across.[\/caption]\r\n\r\nEarth\u2019s interior is broadly divided by composition and depth into crust, mantle, and core (Figure 9.0.2). The crust is primarily (roughly 95%) made up of igneous rock and metamorphic rock with an overall composition between intermediate and felsic. The remaining 5% is made up of sedimentary rock, which is dominated by mudstone.\r\n\r\nThe mantle includes several layers, all with the same overall ultramafic composition. The upper mantle is typically composed of peridotite, a rock dominated by olivine and pyroxene. The lower mantle has a similar chemical composition, but because of the extreme pressures, different minerals are present, including spinels and garnets. The properties of the mantle also vary with depth, as follows:\r\n<ul>\r\n \t<li><strong>[pb_glossary id=\"1212\"]Lithosphere[\/pb_glossary]<\/strong>: solid<\/li>\r\n \t<li><strong>[pb_glossary id=\"1587\"]Asthenosphere[\/pb_glossary]<\/strong>: partially liquid<\/li>\r\n \t<li>Upper and lower mantle: solid but plastic (the difference between the two is in the type of minerals)<\/li>\r\n \t<li><strong>[pb_glossary id=\"1588\"]\"D\" layer[\/pb_glossary]<\/strong> (the part of the mantle within 200 kilometres of the core): partially liquid<\/li>\r\n \t<li>The <strong>[pb_glossary id=\"1589\"]core-mantle boundary[\/pb_glossary]<\/strong> (CMB) is at a depth of 2,900 kilometres.<\/li>\r\n<\/ul>\r\nThe core is primarily composed of iron, with lesser amounts of nickel (about 5%) and several percent oxygen. It is extremely hot (roughly 3500\u00b0 to 5000\u00b0C). The outer core is liquid while the inner core is solid\u2014even though it is hotter\u2014because the pressure is so much greater at that depth.\r\n\r\nAlthough the CMB is just about half of the way to Earth\u2019s centre, the mantle, being on the outside, is by far the major component of Earth. The mantle makes up 82.5% of the volume, the core 16.1%, and the crust only 1.4%.\r\n\r\nIn the remainder of this chapter, we\u2019ll look first at how we know about Earth\u2019s interior structure, and then at the properties of the different layers and the processes that take place within them.<a id=\"retfig9.0.2\"><\/a>\r\n\r\n[caption id=\"attachment_385\" align=\"aligncenter\" width=\"900\"]<a href=\"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/08\/earths-interior-9.png\"><img class=\"wp-image-385\" src=\"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/08\/earths-interior-9.png\" alt=\"\" width=\"900\" height=\"250\" \/><\/a> Figure 9.0.2 Earth\u2019s layers: crust is pink, mantle is green, core is blue. <a href=\"http:\/\/fig9.0.2\">[Image Description]<\/a>[\/caption]\r\n<h3>Image Descriptions<\/h3>\r\n<table id=\"fig9.2\" class=\"aligncenter\" style=\"width: 100%;\" border=\"1\"><caption><a id=\"fig9.0.2\"><\/a>Figure 9.0.2 image description: Layers of the earth<\/caption>\r\n<thead>\r\n<tr>\r\n<th scope=\"col\">Layer<\/th>\r\n<th scope=\"col\">Kilometres below the Earth's surface<\/th>\r\n<th scope=\"col\">Thickness (kilometres)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr>\r\n<td>Crust and Lithospheric part of the mantle<\/td>\r\n<td>0 to 100<\/td>\r\n<td>100<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Asthenosphere and Upper mantle<\/td>\r\n<td>100 to 660<\/td>\r\n<td>560<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Lower mantle<\/td>\r\n<td>660 to 2,700<\/td>\r\n<td>2,040<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>D\" layer<\/td>\r\n<td>2,700 to 2,890<\/td>\r\n<td>190<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Outer liquid core<\/td>\r\n<td>2,890 to 5,100<\/td>\r\n<td>2,210<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Inner solid core<\/td>\r\n<td>5,100 to 6,370<\/td>\r\n<td>1,270<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<a href=\"#retfig9.0.2\">[Return to Figure 9.0.2]<\/a>\r\n<h3>Media Attributions<\/h3>\r\n<ul>\r\n \t<li>Figure 9.0.1 (left):\u00a0 <a href=\"http:\/\/www.nasa.gov\/centers\/goddard\/images\/content\/557996main_tagish-lake-meteorite.jpg\">Tagish Lake meteorite fragment<\/a> \u00a9 Michael Holly. Adapted by Steven Earle. Public domain.<\/li>\r\n \t<li>Figure 9.0.1 (right): <a href=\"http:\/\/upload.wikimedia.org\/wikipedia\/commons\/d\/dc\/Elbogen_meteorite%2C_8.9g.jpg\">Elbogen meteorite, 8.9g<\/a> \u00a9 <a href=\"https:\/\/www.flickr.com\/people\/48082563@N08\">John Taylor<\/a>. Adapted by Steven Earle. <a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/ca\/\">CC BY-SA 2.0<\/a>.<\/li>\r\n \t<li>Figure 9.0.2: \u00a9 Steven Earle. CC BY.<\/li>\r\n<\/ul>","rendered":"<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\">Learning Objectives<\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p>After carefully reading this chapter, completing the exercises within it, and answering the questions at the end, you should be able to:<\/p>\n<ul>\n<li>Explain the variations in the composition and characteristics of Earth\u2019s different layers.<\/li>\n<li>Compare the characteristics and behaviour of the two types of seismic body waves.<\/li>\n<li>Summarize the variations in seismic-wave velocity as a function of rock type and temperature and pressure conditions.<\/li>\n<li>Explain some of the ways that seismic data can be used to understand planetary interiors.<\/li>\n<li>Describe the temperature variations within Earth and their implications for internal processes such as mantle convection.<\/li>\n<li>Explain the origins of Earth\u2019s magnetic field and the timing of magnetic field reversals.<\/li>\n<li>Describe the isostatic relationship between the crust and the mantle, and the implications of that relationship for geological processes on Earth.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<p>In order to understand how Earth works, and especially the mechanisms of plate tectonics (covered in Chapter 10), we need to know something about the inside of our planet \u2014 what it\u2019s made of, and what goes on in there. We have a variety of ways of knowing, and these will be discussed in this chapter, but the one thing we can\u2019t do is go down and look! Fortunately there are a few places where mantle rock is exposed on Earth\u2019s surface, and we have some samples of material from the insides of other planetary bodies, in the form of meteorites that have landed on Earth (Figure 9.0.1). We also have a great deal of seismic information that can help us understand the nature of Earth\u2019s interior.<\/p>\n<figure id=\"attachment_384\" aria-describedby=\"caption-attachment-384\" style=\"width: 900px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/06\/meteorites.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-384\" src=\"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/06\/meteorites.png\" alt=\"\" width=\"900\" height=\"277\" srcset=\"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/06\/meteorites.png 1272w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/06\/meteorites-300x92.png 300w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/06\/meteorites-768x236.png 768w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/06\/meteorites-1024x315.png 1024w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/06\/meteorites-65x20.png 65w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/06\/meteorites-225x69.png 225w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/06\/meteorites-350x108.png 350w\" sizes=\"auto, (max-width: 900px) 100vw, 900px\" \/><\/a><figcaption id=\"caption-attachment-384\" class=\"wp-caption-text\">Figure 9.0.1 Left: a fragment of the Tagish Lake meteorite, discovered in 2000 on the ice of Tagish Lake, B.C. It is a \u201cstony\u201d meteorite that is dominated by ferromagnesian silicate minerals, and is similar in composition to Earth\u2019s mantle. Right: part of the Elbogen meteorite discovered in Germany around 1400. It is an iron meteorite, similar in composition to Earth\u2019s core. Both samples are a few centimetres across.<\/figcaption><\/figure>\n<p>Earth\u2019s interior is broadly divided by composition and depth into crust, mantle, and core (Figure 9.0.2). The crust is primarily (roughly 95%) made up of igneous rock and metamorphic rock with an overall composition between intermediate and felsic. The remaining 5% is made up of sedimentary rock, which is dominated by mudstone.<\/p>\n<p>The mantle includes several layers, all with the same overall ultramafic composition. The upper mantle is typically composed of peridotite, a rock dominated by olivine and pyroxene. The lower mantle has a similar chemical composition, but because of the extreme pressures, different minerals are present, including spinels and garnets. The properties of the mantle also vary with depth, as follows:<\/p>\n<ul>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_386_1212\">Lithosphere<\/a><\/strong>: solid<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_386_1587\">Asthenosphere<\/a><\/strong>: partially liquid<\/li>\n<li>Upper and lower mantle: solid but plastic (the difference between the two is in the type of minerals)<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_386_1588\">\"D\" layer<\/a><\/strong> (the part of the mantle within 200 kilometres of the core): partially liquid<\/li>\n<li>The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_386_1589\">core-mantle boundary<\/a><\/strong> (CMB) is at a depth of 2,900 kilometres.<\/li>\n<\/ul>\n<p>The core is primarily composed of iron, with lesser amounts of nickel (about 5%) and several percent oxygen. It is extremely hot (roughly 3500\u00b0 to 5000\u00b0C). The outer core is liquid while the inner core is solid\u2014even though it is hotter\u2014because the pressure is so much greater at that depth.<\/p>\n<p>Although the CMB is just about half of the way to Earth\u2019s centre, the mantle, being on the outside, is by far the major component of Earth. The mantle makes up 82.5% of the volume, the core 16.1%, and the crust only 1.4%.<\/p>\n<p>In the remainder of this chapter, we\u2019ll look first at how we know about Earth\u2019s interior structure, and then at the properties of the different layers and the processes that take place within them.<a id=\"retfig9.0.2\"><\/a><\/p>\n<figure id=\"attachment_385\" aria-describedby=\"caption-attachment-385\" style=\"width: 900px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/08\/earths-interior-9.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-385\" src=\"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/08\/earths-interior-9.png\" alt=\"\" width=\"900\" height=\"250\" srcset=\"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/08\/earths-interior-9.png 1264w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/08\/earths-interior-9-300x83.png 300w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/08\/earths-interior-9-768x213.png 768w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/08\/earths-interior-9-1024x284.png 1024w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/08\/earths-interior-9-65x18.png 65w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/08\/earths-interior-9-225x62.png 225w, https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-content\/uploads\/sites\/298\/2019\/08\/earths-interior-9-350x97.png 350w\" sizes=\"auto, (max-width: 900px) 100vw, 900px\" \/><\/a><figcaption id=\"caption-attachment-385\" class=\"wp-caption-text\">Figure 9.0.2 Earth\u2019s layers: crust is pink, mantle is green, core is blue. <a href=\"http:\/\/fig9.0.2\">[Image Description]<\/a><\/figcaption><\/figure>\n<h3>Image Descriptions<\/h3>\n<table id=\"fig9.2\" class=\"aligncenter\" style=\"width: 100%;\">\n<caption><a id=\"fig9.0.2\"><\/a>Figure 9.0.2 image description: Layers of the earth<\/caption>\n<thead>\n<tr>\n<th scope=\"col\">Layer<\/th>\n<th scope=\"col\">Kilometres below the Earth&#8217;s surface<\/th>\n<th scope=\"col\">Thickness (kilometres)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Crust and Lithospheric part of the mantle<\/td>\n<td>0 to 100<\/td>\n<td>100<\/td>\n<\/tr>\n<tr>\n<td>Asthenosphere and Upper mantle<\/td>\n<td>100 to 660<\/td>\n<td>560<\/td>\n<\/tr>\n<tr>\n<td>Lower mantle<\/td>\n<td>660 to 2,700<\/td>\n<td>2,040<\/td>\n<\/tr>\n<tr>\n<td>D&#8221; layer<\/td>\n<td>2,700 to 2,890<\/td>\n<td>190<\/td>\n<\/tr>\n<tr>\n<td>Outer liquid core<\/td>\n<td>2,890 to 5,100<\/td>\n<td>2,210<\/td>\n<\/tr>\n<tr>\n<td>Inner solid core<\/td>\n<td>5,100 to 6,370<\/td>\n<td>1,270<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><a href=\"#retfig9.0.2\">[Return to Figure 9.0.2]<\/a><\/p>\n<h3>Media Attributions<\/h3>\n<ul>\n<li>Figure 9.0.1 (left):\u00a0 <a href=\"http:\/\/www.nasa.gov\/centers\/goddard\/images\/content\/557996main_tagish-lake-meteorite.jpg\">Tagish Lake meteorite fragment<\/a> \u00a9 Michael Holly. Adapted by Steven Earle. Public domain.<\/li>\n<li>Figure 9.0.1 (right): <a href=\"http:\/\/upload.wikimedia.org\/wikipedia\/commons\/d\/dc\/Elbogen_meteorite%2C_8.9g.jpg\">Elbogen meteorite, 8.9g<\/a> \u00a9 <a href=\"https:\/\/www.flickr.com\/people\/48082563@N08\">John Taylor<\/a>. Adapted by Steven Earle. <a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/ca\/\">CC BY-SA 2.0<\/a>.<\/li>\n<li>Figure 9.0.2: \u00a9 Steven Earle. CC BY.<\/li>\n<\/ul>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_386_1212\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_386_1212\"><div tabindex=\"-1\"><p>The rigid outer part of the Earth, including the crust and the mantle down to a depth of about 100 kilometres.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_386_1587\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_386_1587\"><div tabindex=\"-1\"><p>the part of the mantle, from about 100 to 200 kilometres below surface, within which the mantle material is close to its melting point, and therefore relatively weak<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_386_1588\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_386_1588\"><div tabindex=\"-1\"><p>(d-double-prime layer) a low seismic velocity zone within the basal 200 km of the mantle<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_386_1589\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_386_1589\"><div tabindex=\"-1\"><p>the boundary, at a 2900 kilometre depth, between the mantle and the core<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"parent":0,"menu_order":9,"template":"","meta":{"pb_part_invisible":false,"pb_part_invisible_string":""},"contributor":[],"license":[],"class_list":["post-386","part","type-part","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-json\/pressbooks\/v2\/parts\/386","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-json\/pressbooks\/v2\/parts"}],"about":[{"href":"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-json\/wp\/v2\/types\/part"}],"version-history":[{"count":4,"href":"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-json\/pressbooks\/v2\/parts\/386\/revisions"}],"predecessor-version":[{"id":2309,"href":"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-json\/pressbooks\/v2\/parts\/386\/revisions\/2309"}],"wp:attachment":[{"href":"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-json\/wp\/v2\/media?parent=386"}],"wp:term":[{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-json\/wp\/v2\/contributor?post=386"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/opentextbc.ca\/physicalgeology2ed\/wp-json\/wp\/v2\/license?post=386"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}