How do scientists know what the interior of the earth looks like when we have never seen it?
http://www.learner.org/courses/essential/earthspace/session3/closer2.html
http://en.wikipedia.org/wiki/Structure_of_the_Earth
Scientists have developed a comprehensive understanding of the Earth's interior through a combination of indirect methods and mathematical models. Although we cannot physically observe the Earth's interior, we can gather information from various sources and use it to make educated inferences. Here are a few key methods scientists use to study the Earth's interior:
1. Seismic Waves: One of the most important sources of information about the Earth's interior comes from studying seismic waves generated by earthquakes or artificial sources. Seismic waves travel through the Earth's layers and behave differently depending on the properties of the materials they encounter. By analyzing how seismic waves behave and the time it takes for them to travel, scientists can deduce valuable information about the composition, density, and structure of the Earth's interior.
2. Earthquake Waveform Analysis: Seismologists use an extensive network of seismometers to record the seismic waves produced by earthquakes worldwide. By studying the patterns and characteristics of these waveforms, scientists can understand the properties of the materials the waves have passed through. This helps them infer the existence of different layers, such as the crust, mantle, outer core, and inner core.
3. Gravitational Measurements: The Earth's gravitational field is influenced by the distribution of mass within it. By measuring variations in gravity across different regions, scientists can make inferences about variations in density and composition. This information helps in understanding the structure of the Earth's interior.
4. Volcanic and Mantle Rocks: The materials brought to the surface through volcanic eruptions provide valuable clues about the composition and properties of the Earth's interior. By analyzing volcanic rocks, scientists can gain insights into the nature of the mantle, which is the layer beneath the Earth's crust.
5. Laboratory Experiments: Scientists conduct experiments in laboratories to recreate the extreme conditions that exist deep within the Earth. Using high-pressure and high-temperature apparatus, they can simulate the physical and chemical properties of the Earth's interior. These experiments allow researchers to measure the behavior and properties of various materials under conditions similar to those found in the Earth's deep interior.
By combining the data and insights derived from these methods, scientists have developed sophisticated models of the Earth's interior. These models are constantly refined in light of new data and observations, enabling us to have a comprehensive understanding of the composition, structure, and dynamics of the Earth's deep interior, even though we have never directly seen it.