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}}</ref> Cosmic rays are composed primarily of high-energy [[proton]]s and [[atomic nuclei]]. They are of mysterious origin. They were given the name "rays" in the mistaken belief that they were a form of electromagnetic radiation.  However, cosmic rays are particles rather than just photons.  Due to relativistic effects, cosmic rays have a very high mass and reach energies of up to 10¹⁴ eV.

}}</ref> Cosmic rays are composed primarily of high-energy [[proton]]s and [[atomic nuclei]]. They are of mysterious origin. They were given the name "rays" in the mistaken belief that they were a form of electromagnetic radiation.  However, cosmic rays are particles rather than just photons.  Due to relativistic effects, cosmic rays have a very high mass and reach energies of up to 10¹⁴ eV.

=== Discovery ===

== Discovery ==

In 1909 [[Theodor Wulf]] developed an [[electrometer]], a device to measure the rate of ion production inside a hermetically sealed container. Wulf used it to find higher levels of radiation at the top of the [[Eiffel Tower]] than at its base. However, his paper was not widely accepted. In 1911, [[Domenico Pacini]] wanted to determine if ionizing radiation came from the Earth or from other sources.  He measured simultaneous variations of the rate of ionization over a lake, over the sea, and at a depth of 3 meters from the surface. His measurements suggested that there was a source other than just the Earth.<ref>

In 1909 [[Theodor Wulf]] developed an [[electrometer]], a device to measure the rate of ion production inside a hermetically sealed container. Wulf used it to find higher levels of radiation at the top of the [[Eiffel Tower]] than at its base. However, his paper was not widely accepted. In 1911, [[Domenico Pacini]] wanted to determine if ionizing radiation came from the Earth or from other sources.  He measured simultaneous variations of the rate of ionization over a lake, over the sea, and at a depth of 3 meters from the surface. His measurements suggested that there was a source other than just the Earth.<ref>

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==Effects==

==Effects==

Cosmic rays react with Nitrogen and Oxygen in the Earth's atmosphere that among other things results in Ozone depletion.  Cosmic rays also react with Carbon to form Carbon-14.  Until the time of nuclear testing, the amount of ¹⁴C has been relatively constant, which is the basis for carbon-dating of materials.

Cosmic rays react with Nitrogen and Oxygen in the Earth's atmosphere that among other things results in Ozone depletion.  Cosmic rays also react with Carbon to form Carbon-14.  Until the time of nuclear testing, the amount of ¹⁴C has been relatively constant, which is the basis for carbon-dating of materials.