Laboratory Techniques and Earth’s Interior Study Methods

Posted on Dec 15, 2024 in Geology

Laboratory Techniques

Physics Methods

  • Petrographic Microscope: This is a general-purpose instrument of the geological laboratory, which serves to distinguish minerals. The lenses are called Nicols and are polarizing. Located below the stage, it transmits plane-polarized light. The analyzer is located below the stage and transmits plane-polarized light.
  • Electron Microscope: It’s a more powerful and versatile tool that can be used in geological research.
  • X-Ray Diffraction: This is a radiation that was unknown, enough to penetrate opaque bodies.
  • Scale Model and Essay

Chemical Methods

  • Chemical Analysis: The common and simple techniques are: volumetric analysis, which is to determine the volume of a solution, and gravimetric analysis, in which the target substances are made to precipitate into poorly soluble substances.
  • Spectroscopy: The spectroscopic methods are more specific and complex. They are based on the measurement of the amount and type of radiation.
  • X-ray fluorescence spectrometry is a fast technique that allows knowing the composition of a solid substance.
  • Atomic absorption spectrophotometry consists of passing a vapor atom through monochromatic light.

Methods of Studying the Interior of the Earth

Direct Methods

This consists of direct observation of the materials that make up our planet or some of its physical properties. The geological surveys are conducted by polling, which bits or drills the ground, and an exhaust pipe can obtain a column of surface material called a core sample. It is used to learn the geological structure of the land (wells and gathering poll rocks, volcanoes, and basic acids, shallower to deeper, meteorites).

Indirect Methods

  • Earth’s Density: To calculate the density of the Earth, it is necessary to know its mass and its volume. To perform the calculation of volume, given that the Earth is an ellipsoid of revolution whose polar radius is 6356 km and equatorial radius is 6378 km. As the difference between the two radii is very small (22 km), we can approximate the volume of a sphere: V = 4/3 · π · R3 and obtain the volume of 1080.109 km3.
  • Gravimetry: The acceleration of gravity on Earth is given by the equation: g = G · M / R2. The values of g vary depending on the point of the Earth’s surface because the Earth is not a perfect sphere; the polar radius is 22 km less than the equatorial radius.
  • Study of the Temperature: The temperature inside the Earth increases with depth at 3 degrees Celsius per 100m depth. This magnitude is called the geothermal gradient. But the geothermal gradient only maintains its value during the first 30-50 km of depth; at greater depths, the geothermal gradient decreases.
  • Study of Terrestrial Magnetism: The Earth’s magnetic field has produced local variations due to the differences in the materials constituting the Earth’s crust. These variations are called magnetic anomalies. The Earth’s magnetic poles do not coincide with the geographical poles, but are located at some distance from them. To study the magnetic field, a magnetometer is used, which measures the magnetic field values.
  • Electrical Methods: Based on changes in electrical conductivity of the rocks. The electrical conductivity of the rocks is generally very low; the magnitude is usually measured inversely, as electrical resistivity. ρ = K · V / I.
  • Study of Meteorites: Meteorites are solids that enter the orbit of Earth. They can be classified into:
    • Achondrites: Represent 9% of meteorites. They are made of calcium silicates of iron and magnesium and are similar to the oceanic crust.
    • Chondrites: Assume 86% of the meteorites. They are composed of magnesium silicates, are very similar to peridotites, and represent the Earth’s mantle.
    • Siderites: Assume 4%, are made up primarily of iron and to a lesser extent, nickel, and are similar to the Earth’s core.
    • Siderolites: They represent 1% and are composed of iron and silicate, and their composition is similar to the Earth’s core.
  • Seismic Methods: The data has contributed more. It is based on the study of seismic waves. In the hypocenter, two types of seismic waves are generated:
    • Primary or P-waves are the fastest: They travel at speeds of 6 to 13 km/s. The particles vibrate in the same direction in which the wave is transmitted.
    • Secondary or S-waves are slower, spreading at speeds of 3 to 8 km/s. They are not transmitted through fluids, and particles vibrate transversely to the direction of propagation, so they are transverse waves.
  • Seismic Discontinuities: The inner regions of the world where seismic waves are reflected and refracted, separating layers of different composition or different physical states. We can distinguish two groups:
    • First-order discontinuities: Mohorovičić and Gutenberg.
    • Second-order discontinuities: Transition areas of the mantle and transition zone of the nucleus.