Earth Structure

Earth layered structure. (1) inner core; (2) outer core; (3) lower mantle; (4) uppper mantle; (5) lithosphere; (6) crust

Advances in seismology, computer modelling, and mineralogy and crystallography at high temperatures and pressures give insights into the internal composition and structure of the Earth.

Earth layered structure. Typical wave paths from earthquakes like these gave early seismologists insights into the layered structure of the Earth

Seismologists can use the arrival times of seismic waves in reverse to image the interior of the Earth. Early advances in this field showed the existence of a liquid outer core (where shear waves were not able to propagate) and a dense solid inner core. These advances led to the development of a layered model of the Earth, with a crust and lithosphere on top, the mantle below (separated within itself by seismic discontinuities at 410 and 660 kilometers), and the outer core and inner core below that. More recently, seismologists have been able to create detailed images of wave speeds inside the earth in the same way a doctor images a body in a CT scan. These images have led to a much more detailed view of the interior of the Earth, and have replaced the simplified layered model with a much more dynamic model.

The seismically-imaged Farallon Plate subducting beneath North America. The only remnants of this plate on the Surface are the Juan de Fuca Plate and Explorer plate in the Northwestern USA / Southwestern Canada, and the Cocos Plate on the west coast of Mexico.

Mineralogists have been able to use the pressure and temperature data from the seismic and modelling studies alongside knowledge of the elemental composition of the Earth at depth to reproduce these conditions in experimental settings and measure changes in crystal structure. These studies explain the chemical changes associated with the major seismic discontinuities in the mantle, and show the crystallographic structures expected in the inner core of the Earth.

What Does a Geologist Do?

Geologists work to understand the history of our planet. The better they can understand Earth’s history the better they can foresee how events and processes of the past might influence the future. Here are two examples:


Volcanic Mudflow Hazard Map by USGS
1) The processes acting upon the Earth cause hazards such as landslides, earthquakes and volcanic eruptions. Geologists are working to understand these processes well enough to avoid building important structures where they will be damaged. If geologists learn a lot about volcanic mudflows of the past then that information can be very useful in predicting the dangerous areas where volcanic mudflows might strike in the future. The map at right shows areas that are thought to be at risk from future mudflows around Mount Rainier. Intelligent people should be cautions when considering activities or property development in these areas. (Click on the map to see greater detail.)

2) Geologists have worked hard to learn that oil and natural gas form from organic materials deposited along the margins of continents and in shallow seas upon the continents. They have also learned to recognize the types of rock that are deposited in these near-shore environments. This knowledge enables them to recoginze potential oil and natural gas source rocks. In the photo below oil field workers are placing a tool into an oil exploration well. This tool will be lowered down the hole and will record tiny amounts of radioactivity released from the rocks below (rocks rich in organic materials frequently contain tiny amounts of radioactive materials). The information obtained from the tool will help them assess the oil and natural gas production potential of the rocks below. If they do these tests at many locations within a region they might be able to map an oil or natural gas field.