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Why is technetium not found as a primordial element in Earth’s crust?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — transition metal Modern version of the periodic table of the elements (printable).

Technetium is not found as a primordial element in Earth’s crust because all of its isotopes are radioactive and possess relatively short half-lives.12

For an element to be considered primordial, it must have existed since the formation of the Earth approximately 4.5 billion years ago. Because even the most stable isotope of technetium, technetium-97, has a half-life that is far too short to have survived since the planet's formation, any original supply of the element would have long since decayed into other substances.12

While minute traces of technetium can be found in the Earth's crust today, these are not primordial; rather, they are continually produced through the spontaneous fission of uranium. Consequently, technetium is classified as a synthetic transition metal, as it is primarily obtained through artificial production in nuclear reactors.123