3. Interior Structure


Using information about Mars' mass, size and the structure of its gravity field, scientists have determined the different densities of Mars' interior structure. 
  • Mars' core has twice the concentration of lighter elements than the Earth, and is probably made from iron, nickel and sulphur (a lighter element) and is partially fluid. 
  • The mantle and crust are both made from silica rich rocks. 
  • Mars crust is much thicker than Earth, between 50 - 125 km deep (compared to Earth's average of 40 km - see diagram below).
Mars cooled down faster than the Earth because it was much smaller. There is no evidence of recent volcanic activity on Mars. Mars' core is no longer active.


As we learned earlier, heat energy in the Earth's core is left over from the formation of the planet and from on-going radioactive decay. This heat energy radiates upwards through the Earth's layers.

Before we take a look at the Earth's interior structure, be aware that names and definitions of the layers change, depending on what you're talking about.

The chemical composition divides the Earth into three layers
      • Crust - the uppermost, thinest layer of solid, silica (SiO2) rich rocks.
      • Mantle - the biggest layer of molten rock (silica rich). The rocks are firm at the topmost layer and liquid on the bottom.
      • Core - mostly iron (Fe) with some nickel (Ni).
The physical properties are divided into five layers.
  • Lithosphere - crust, and rigid part of the upper mantle (solid rock)
  • Athenosphere - the plastic part of the mantle (molten rock)
  • Mesosphere - in deeper parts of the mantle the molten rocks are under such enormous pressure they are forced in a denser, more rigid structure (solid molten rock).
  • Outer core - is mostly composed of liquid iron.
  • Inner core - the inner core is so hot, and under such intense pressure that it remains solid.


Before we find out how we know about the deep structures of the Earth, let's look at the crust. The crust is also part of the lithosphere, which sits on the plastic, hot asthenosphere (or more simply, the crust sits on the upper mantle).

On Earth, there are two major types of crust:
  • Continental Crust is mostly made from granite, and is lighter and thicker than:
  • Oceanic Crust , which is mostly made from basalt and is thinner and heavier than the continental crust.
TASK 7: Use the following resources (and/or others) to create an annotated diagram (with labels) that identifies and explains the different layers of the Earth. Include chemical composition, temperature, depth of layer, and whether its a solid, plastic, or liquid. Extra points for any extra interesting information. Paste your diagram into your notebook.
Information about the Structure of the Earth.

TASK 8: Read the Graph of the Earth's Layers and answer the questions. 

Next we'll find out how scientists used earthquakes to find out what's inside the Earth.