How far above Earth do traces of gaseous elements such as helium extend in the atmosphere?

Traces of gaseous elements, including helium, can be found in the Earth's atmosphere extending to significant altitudes, particularly within the thermosphere. The thermosphere starts around 50 miles above the Earth's surface and can extend up to about 300 miles, but certain lighter elements and gases can be found at even higher altitudes.

Helium is one of the lighter elements and can be present in very small amounts in the upper atmosphere due to its low atomic mass, which allows it to escape the gravitational pull of the Earth more easily than heavier elements.

While the main concentration of helium occurs well below the 18,000-mile mark, it is important to note that the exosphere, which begins around 300 miles above the Earth and extends up to about 6,200 miles, contains very dilute amounts of various gases, including helium. However, the higher estimate of 18,000 miles reflects a broader understanding that, under certain conditions, such elements can linger at altitudes where atmospheric density is extremely low.

Thus, the correct understanding of the distribution of helium and similar gases indicates that the traces of these elements extend throughout significant portions of the upper atmosphere, making the choice of 18,000 miles a plausible estimate for scenarios where