MadSci Network: Earth Sciences
Query:

Re: What is the mass and volume percentages of certian layers of the earth?

Date: Tue Nov 16 22:24:28 1999
Posted By: Tye Morancy, MadSci Admin
Area of science: Earth Sciences
ID: 939996546.Es
Message:

Hello,

Ok, here is my lengthy reply to your question...let's see if I can cover all the bases... :)

The earth is made up of five parts, or layers so to speak.

  1. The Atmosphere, which is gaseous.
  2. The Hydrosphere, which represents that part of the earth which is liquid water, such as the lakes, seas, and oceans.
  3. The Lithosphere, which is the uppermost crust of the earth, which is the layer that you are standing on.
  4. The Mantle, which is the layer of rock and metal beneath the Lithosphere.
  5. The Core, which is the very hot center of the planet made of iron and crystals.
I performed several calculations for each layer based on the materials in them, their thickness, volume, and density, which I will explain as we go. So, let's take it in parts and see what we get.

The atmosphere is the gaseous envelope that surrounds the solid body of the planet. Although it has a thickness of more than 1100 km (more than 700 mi), about half its mass is concentrated in the lower 5.6 km (3.5 mi). The gases within it are mostly Nitrogen and Oxygen, which we breathe. I calculated the volume of the air to be approximately :

                  volume = 7.081 x10^20 cubic meters  
                  assuming an average density of 1.2 kg/m3 which   
                                decreases as we increase altitude 
                  mass = 8.497 x10^20 kg     = 0.014% of earth's mass
                                               38% of earth's volume
The lithosphere, consisting mainly of the cold, rigid, rocky crust of the earth extends to depths of 100 km (60 mi). The rocks of the lithosphere have an average density of 2.7 g/cm3 and are almost entirely made up of 11 elements, which together account for about 99.5 percent of its mass. The most abundant is oxygen (about 46.60 percent of the total), followed by silicon (about 27.72 percent), aluminum (8.13 percent), iron (5.0 percent), calcium (3.63 percent), sodium (2.83 percent), potassium (2.59 percent), magnesium (2.09 percent) and titanium, hydrogen, and phosphorus (totaling less than 1 percent). In addition, 11 other elements are present in trace amounts of 0.1 to 0.02 percent. These elements, in order of abundance, are carbon, manganese, sulfur, barium, chlorine, chromium, fluorine, zirconium, nickel, strontium, and vanadium. The elements are present in the lithosphere almost entirely in the form of compounds rather than in their free state. These compounds exist almost entirely in the crystalline state, so they are, by definition, minerals.

The lithosphere comprises two shells :the crust and upper mantle that are divided into a dozen or so rigid tectonic plates. The crust itself is divided in two. The sialic or upper crust, of which the continents consist, is made up of igneous and sedimentary rocks whose average chemical composition is similar to that of granite and whose density is about 2.7 g/cm3. The simatic or lower crust, which forms the floors of the ocean basins, is made of darker, heavier igneous rocks such as gabbro and basalt, with an average density of about 3. Taking all of this and some other factors into consideration, we get:

              volume = 5.054 x10^19 cubic meters 
              density of 2.7 g/cm3 
              mass = 1.365 x10^23 kg      =  2.18 % of earth's mass
                                          =  2.72 % of earth's volume
The mantle extends from the base of the crust to a depth of about 2900 km (1800 mi). Except for the zone known as the asthenosphere, it is solid, and its density, increasing with depth, ranges from 3.3 to 6 g/cm3. The upper mantle is composed of iron and magnesium silicates. The lower part may consist of a mixture of oxides of magnesium, silicon, and iron.This layer is made up of mostly 11 elements : oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium, titanium, hydrogen, and phosphorous. These 11 elements are all mixed up within different compounds in a crystal form, so that we can call them minerals. For this layer we calculate a value of:
              volume = 9.199 x10^20 cubic meters 
              density ranges from 3.3 g/cm3 (upper mantle) to 
                                  6.0 g/cm3 (lower mantle)
              mass = 4.278 x10^24 kg      =   68.4 % of earth's mass
                                          =   49.5 % of earth's volume    
The Hydrosphere is the layer of water which covers about 71% of the earth's surface. This layer is the combination of rivers, seas, lakes, underground water, and all the world's oceans. The average depth of the oceans is 3794 m (12,447 ft), more than five times the average height of the continents. The mass of the oceans is approximately 1.35 quintillion (1.35 10^18) metric tons, or about 1/4400 of the total mass of the earth. This is 0.04 % of the earth's mass.

The Core is the center part of the earth and is actually divided into an outer core and inner core. Seismological research has shown that the core has an outer shell about 2225 km (1380 mi) thick with an average density of 10 g/cm3. This shell is probably rigid, and studies show that its outer surface has depressions and peaks, the latter forming where warm material rises. From this we can calculate :

           volume = 1.719 x10^20 cubic meters 
           density of 10 g/cm3
           mass = 1.719 x10^24 kg      =   27.5 % of earth's mass
                                       =   9.25 % of earth's volume
In contrast, the inner core, which has a radius of about 1275 km (795 mi), is solid. Both core layers are thought to consist largely of iron, with a small percentage of nickel and other elements. Temperatures in the inner core may be as high as 6650C (12,000F), and the average density is estimated to be 13 g/cm3. Phew!!! The values we can determine for the inner core are :
          volume = 8.939 x10^18 cubic meters 
          density of 13 g/cm3 
          mass = 1.162 x10^23 kg      =   1.86 % of earth's mass
                                      =   0.48 % of earth's volume
The entire earth weighs 6 thousand, billion, billion tons!!! I hope this helped you out...thank you for the question...

Tye Morancy
"Mad Scientist"


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