The Core of the Earth | 100 Greatest Discoveries

Science Channel

8 Jan 201402:39

Summary

TLDRIn the late 19th century, British geologist Richard Oldham discovered the Earth's core after noticing seismic waves from an earthquake were deflected, suggesting a dense inner mass. Decades later, Danish seismologist Inge Lehmann identified a second boundary within the core, revealing the Earth has two cores. The inner core, discovered by Lehmann, is a solid iron sphere under immense pressure, while Oldham's outer core is a liquid iron and element mix generating Earth's magnetic field. Together, these cores form a structure larger than Mars, with temperatures at the core's center exceeding the Sun's surface by 2,000 degrees Fahrenheit.

Takeaways

🌏 In 19:06, British geologist Richard Oldham discovered the Earth's core while analyzing seismograph readings from a large earthquake.
🔍 Oldham noticed that seismic waves did not reach the center of the Earth as expected, indicating the presence of a dense mass that deflected the waves.
🎯 This dense mass was identified as the innermost part of the Earth, the core, which was a significant discovery for understanding the Earth's structure.
👩‍🔬 Danish seismologist Inge Lehmann challenged the then-complete picture of the Earth's core in the early 1930s.
🌋 Lehmann's analysis of seismic waves from an earthquake revealed a change in velocity, suggesting another boundary within the Earth's core.
🌐 She proposed that the Earth has not one but two cores, which was a revolutionary idea at the time.
🔧 Modern seismic measurements confirm that the Earth's inner core, discovered by Lehmann, is solid iron, while the outer core, discovered by Oldham, is liquid iron and other elements.
🌌 The outer core generates electric currents that create the Earth's magnetic field, which protects the planet from harmful cosmic radiation.
🔥 The combined structure of the two cores spans over 4,000 miles in diameter, larger than Mars.
🌡️ At the center of the core, temperatures can reach up to 13,000 degrees Fahrenheit, which is hotter than the surface of the Sun.

Q & A

Who was Richard Oldham and what did he discover?
-Richard Oldham was a British geologist who discovered the Earth's core while analyzing seismograph readings from a large earthquake. He noticed that the seismic waves did not travel all the way to the center of the Earth as expected, indicating the presence of a dense mass that deflected the waves.
What was unusual about the seismic waves observed by Richard Oldham?
-The unusual observation was that the seismic waves from the earthquake did not reach the center of the Earth as anticipated. Instead, they appeared to have been deflected by an obstacle, which Oldham identified as the Earth's core.
Who was Inge Lehmann and what was her contribution to the understanding of the Earth's core?
-Inge Lehmann was a Danish seismologist who, through her analysis of seismic waves from earthquakes, discovered that the Earth has not one but two cores. She identified a change in the velocity of the seismic waves as they passed through the Earth's core, suggesting the presence of an inner core.
What is the difference between the Earth's inner core and outer core?
-The Earth's inner core, discovered by Inge Lehmann, is a solid mass of iron and is located at the center of the Earth. It is under immense pressure, approximately three million times the pressure at the Earth's surface. The outer core, discovered by Richard Oldham, is a liquid layer of iron and other elements that surrounds the inner core and generates electric currents, creating the Earth's magnetic field.
What is the composition of the Earth's inner core?
-The Earth's inner core is composed primarily of solid iron, existing under extreme pressure and temperatures that can reach up to 13,000 degrees Fahrenheit.
How does the outer core contribute to the Earth's magnetic field?
-The outer core, being a hot, churning mass of liquid iron and other elements, generates electric currents. These currents, in turn, create the magnetic field that shields the Earth from harmful cosmic radiation.
What is the diameter of the combined structure of the Earth's two cores?
-The combined structure of the Earth's two cores, the inner and outer core, has a diameter of over 4,000 miles, which is slightly larger than the planet Mars.
How does the temperature at the center of the Earth's core compare to the surface of the Sun?
-The temperature at the center of the Earth's core can reach as high as 13,000 degrees Fahrenheit, which is approximately 2,000 degrees hotter than the surface of the Sun.
What role did the seismic waves from earthquakes play in the discovery of the Earth's core?
-Seismic waves from earthquakes were crucial in the discovery of the Earth's core. By analyzing how these waves traveled through the Earth and noting changes in their velocity, scientists like Richard Oldham and Inge Lehmann were able to infer the existence and properties of the Earth's core.
What was the significance of Oldham's and Lehmann's discoveries regarding the Earth's core?
-The discoveries by Oldham and Lehmann were significant as they revolutionized our understanding of the Earth's interior structure. Their findings laid the groundwork for further geological research and helped explain phenomena such as the Earth's magnetic field.

Outlines

00:00

🌏 Discovery of Earth's Core

British geologist Richard Oldham discovered the Earth's core in 1906 while analyzing seismograph readings from a large earthquake. He noticed that seismic waves did not travel to the center of the Earth as expected, indicating an obstacle. This obstacle was identified as the dense innermost part of the Earth, the core. Oldham's discovery laid the groundwork for further studies on the Earth's interior.

🔍 Lehmann's Findings on Earth's Dual Core

In the 1930s, Danish seismologist Inge Lehmann questioned the accepted model of the Earth's core. Through her analysis of seismic waves from an earthquake recorded by stations worldwide, she detected a change in velocity, suggesting another boundary within the Earth's core. This led to the realization that the Earth has two cores: the inner core, which she identified, and the outer core discovered by Oldham. The inner core is solid iron, while the outer core is liquid iron and other elements, generating electric currents that create Earth's magnetic field.

Mindmap

Keywords

💡Seismograph

A seismograph is an instrument that measures and records seismic waves caused by earthquakes, volcanic activity, or other geological events. In the video, British geologist Richard Oldham used seismograph readings to analyze the vibrations from a large earthquake, which led to the discovery of the Earth's core. The seismograph's data was crucial in understanding how seismic waves behaved as they traveled through the Earth, indicating the presence of different layers within the planet.

💡Seismic Waves

Seismic waves are the vibrations that travel through the Earth's layers following an earthquake or other seismic event. They are the primary means by which seismologists study the Earth's interior. In the script, the odd behavior of seismic waves as they did not reach the center of the Earth as expected led Oldham to the realization of the Earth's core. The change in velocity of these waves, as noted by Inge Lehmann, also indicated the presence of another boundary, revealing the existence of the inner core.

💡Earth's Core

The Earth's core is the innermost part of the planet, consisting of two distinct layers: the inner core and the outer core. The discovery of the core by Richard Oldham was a significant milestone in understanding the Earth's structure. The video emphasizes that the core is a dense mass that deflected seismic waves, indicating its solid and liquid composition. The core plays a vital role in generating the Earth's magnetic field and protecting the planet from cosmic radiation.

💡Inge Lehmann

Inge Lehmann was a Danish seismologist who made significant contributions to the understanding of the Earth's interior. Her work in the 1930s led to the discovery of the Earth's inner core. The video highlights her skepticism about the accepted model of the Earth's core and her analysis of seismic waves, which revealed a change in velocity, suggesting the presence of another boundary within the Earth. Lehmann's findings were instrumental in refining the model of the Earth's core.

💡Inner Core

The inner core of the Earth is the solid, innermost part of the planet's core, primarily composed of solid iron. The video explains that gravity at the center of the Earth creates immense pressure, which is why the inner core is solid. This core is crucial for understanding the Earth's structure and the dynamics of its magnetic field. The script mentions that the inner core is discovered by Inge Lehmann and is part of the two-core system that Oldham and Lehmann helped identify.

💡Outer Core

The outer core is the liquid layer surrounding the Earth's solid inner core, composed mainly of liquid iron and other elements. As described in the video, this layer generates electric currents due to its churning motion, which in turn creates the Earth's magnetic field. The outer core's discovery by Richard Oldham was pivotal in understanding the Earth's protective magnetic field and the dynamics of its interior.

💡Magnetic Field

The Earth's magnetic field is a protective force that shields the planet from harmful cosmic radiation. Generated by electric currents in the Earth's outer core, the magnetic field is essential for the survival of life on Earth. The video explains that the churning motion of the liquid outer core creates these currents, highlighting the importance of the core's composition and behavior in maintaining the Earth's magnetic field.

💡Cosmic Radiation

Cosmic radiation consists of high-energy particles originating from outer space that can be harmful to life on Earth. The video mentions that the Earth's magnetic field, influenced by the core's activity, protects the planet from this radiation. Understanding the core's role in generating the magnetic field is, therefore, crucial for comprehending how the Earth is shielded from these potentially damaging particles.

💡Seismological Stations

Seismological stations are facilities that monitor and record seismic activity, such as earthquakes. They play a vital role in seismology by providing data that helps scientists analyze and understand the Earth's interior. In the video, Inge Lehmann used recordings from these stations to analyze seismic waves from an earthquake, leading to the discovery of the inner core. The network of seismological stations around the world is essential for global seismic monitoring and research.

💡Velocity of Seismic Waves

The velocity of seismic waves refers to the speed at which these waves travel through the Earth's layers. Changes in velocity can indicate the presence of different materials or boundaries within the Earth. In the video, Inge Lehmann's analysis of the velocity changes of seismic waves as they passed through the Earth's core led to the discovery of the inner core. Understanding the velocity of seismic waves is key to deciphering the structure and composition of the Earth's interior.

💡Pressure

Pressure in the context of the Earth's core refers to the immense force exerted by the weight of the overlying rock and material. The video states that the pressure at the center of the Earth is three million times greater than at the surface. This extreme pressure is responsible for the solid state of the inner core, as it is so high that it overrides the melting point of the core materials. Understanding the pressure within the Earth's core is essential for comprehending its physical state and the behavior of seismic waves.

Highlights

British geologist Richard Oldham discovered the Earth's core while analyzing seismograph readings.

Seismic waves from an earthquake did not reach the center of the Earth as expected, indicating an obstacle.

Oldham concluded that the obstacle was the dense innermost part of the Earth, the core.

Oldham's discovery was pivotal for understanding the Earth's interior structure.

Danish seismologist Inge Lehmann questioned the accepted model of the Earth's core in the 1930s.

Lehmann's analysis of seismic waves from an earthquake revealed a change in velocity within the Earth's core.

Lehmann proposed that the Earth has two cores, not just one.

The inner core, discovered by Lehmann, is made of solid iron.

Gravity at the Earth's center creates immense pressure, three million times that on the surface.

The outer core, discovered by Oldham, is composed of liquid iron and other elements.

The outer core generates electric currents that create Earth's magnetic field, protecting it from cosmic radiation.

Together, the two cores form a structure over 4,000 miles in diameter, larger than Mars.

The temperature at the center of the core can reach up to 13,000 degrees Fahrenheit, hotter than the Sun's surface.

Seismic measurements have allowed for precise understanding of the Earth's core structure.

The discovery of the Earth's core has had a profound impact on the study of Earth's geology and physics.

Oldham and Lehmann's work revolutionized our understanding of the Earth's interior.