During the Middle Ages miners began to notice that the deeper they dug into the Earth's surface the warmer it became. The physicist Kelvin came up with a theory that the Earth's started off hot and has been cooling down ever since. Kelvin was confident this idea would allow him to determine the age of our planet. Was Kelvin's theory correct? Watch and learn. [2:47]

Concepts

radioactivity

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Additional Tags

earth's surface, kelvin scale, why is it hot underground?, physical processes of earth's surface

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Classroom Considerations

• Knovation Readability Score: 1 (1 low difficulty, 5 high difficulty)

• This video is hosted on YouTube