Our understanding of the Earth's interior has been at the center of scientific studies for several decades, recognized in the early 1900s. Over the years , scientists debated and argued over their discoveries, observations and theories to find the most correct model of the composition and internal structure of the Earth. Earthquakes play a major role in understanding the composition and materials that exist within the Earth (Merali and Skinner, 2009, p.252). Earthquakes are the primary source of information about the internal workings of the Earth, due to the nature of the seismic waves they produce. P and S waves are reflected and refracted at different boundaries within the Earth, allowing seismologists to draw conclusions about the internal composition and structure of planet Earth. (Merali and Skinner, 2009, p.252). In 1906, a scientist named Richard Dixon Oldham had suggested a theory structured by the findings of another scientist named Emil Wiechert. Oldham had identified that S and P waves behaved differently and could be used to explain and illustrate that previous theories were not entirely correct (Merali and Skinner, 2009, p.253). Through analysis of the arrival times of these waves, Oldham had concluded that p- and s-waves reacted differently in terms of refraction, reflection, or absorption depending on the state of the material, as shown in Figure 1.(Tarbuck, Lutgens, Tasa, 2013, p.143). Oldham had developed this theory that the Earth is not in the same state due to the seismic discontinuity effects shown in Figure 1, consisting of refraction, reflection and absorption. The changes shown from this idea are: the wave speed due to a refraction occurs...... middle of paper ...... the composition of the core and mantle (Merali and Skinner, 2009, p.259), (Tarbuck, Lutgens, Tasa, 2013, p.397-406). Ultimately, the development of previous inferences and observations that developed our current model for the composition and interior structure of the Earth are a key concept for understanding our future developments towards supplying our planet and understanding how it works. to a higher degree.BibliographyMerali Z., Skinner B.,2009, Visualizing Earth Science, 1st Ed, John Wiley and Sons, Hoboken, New Jersey.Tarbuck E., Lutgens F., Tasa D., 2014, An Introduction to Physical Geology, 5th edition, Pearson Education, Upper Saddle River, New Jersey. Elsasser W., 1950, Review of Modern Physics, The Earth's Interior and Geomagneism, 22, 2-20. Herndon J. M, 2005, Current Science, Scientific Basis of knowledge of the composition of the Earth, 88, 1034-1036)