Cosmic Abundance of Elements | Geology Optional Notes for UPSC PDF Download

Cosmic Abundances

• Elements are the fundamental building blocks of ordinary matter, with 93 elements recognized as naturally occurring.
• Additionally, there exist 20 artificial elements that can be created in laboratories by bombarding nuclei with high-energy particles like α-particles.
• These artificially produced elements are unstable and have very short lifespans, hence they are not found in nature.
• Most natural elements are present on Earth, with a few exceptions discovered in other celestial bodies within the solar system.
• Remarkably, the same 93 elements identified on Earth are also distributed throughout the universe, maintaining similar proportions as in the solar system.

Chemical Composition of the Universe

• The chemical composition of the universe denotes the variety of elements present and their respective quantities.
• Given the similarity between the chemical compositions of the universe and the solar system, discussing one essentially encompasses the other.
• The relative distribution of elements in the universe is termed cosmic abundances.

Determination of Cosmic Abundances

• In the quest to understand cosmic abundances, various methods are employed to gather relevant information:
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  • The Earth serves as a primary source for abundance data. Scientists analyze samples from diverse locations on Earth in laboratories to determine elemental compositions.
  • The Sun plays a crucial role in this determination. Fraunhofer lines in the solar spectrum, which are absorption lines, reveal the presence of elements in the Sun's atmosphere. By comparing these lines with known element spectra, scientists can identify and quantify elements.
  • The solar atmosphere, including the chromosphere and corona, emits specific spectral lines that aid in determining solar system abundances.
  • Analysis of solar wind and solar cosmic rays, through instruments on spacecraft, provides direct insights into the composition of these solar emissions.
  • Objects within the solar system, like the moon, planets, and meteors, offer valuable abundance information. For instance, meteorites that survive atmospheric entry can be analyzed to understand elemental compositions.
  • Beyond our solar system, studying the spectra of stars and interstellar clouds offers valuable data on cosmic abundances.

Cosmic Element Abundances

Main Points:

• Hydrogen (H1) and helium (He4) dominate the universe's elemental composition, with hydrogen constituting about 90% of all particles and helium around 10%.
• Elements heavier than hydrogen and helium make up less than 1% of the total matter in the universe.
• Elemental abundances generally rise with mass number up to iron (Fe56), where a peak is observed.
• Beyond mass number 60, elemental abundances decline, starting rapidly before gradually slowing down.
• Abundance peaks occur at elements with mass numbers in multiples of 4 (e.g., 12, 16) and multiples of 2 (e.g., 14, 18), which are more prevalent compared to odd mass number elements.

Cosmic Abundance Data Summary

Main Conclusions:

• The origins of hydrogen and helium differ from the origin of heavier elements in the universe.
• Abundance peaks at mass numbers that are multiples of four may involve particles like the α-particle or the helium nucleus, which has a mass of 4 atomic mass units (amu).

The Formation of Elements in Stars

• Question for Cosmic Abundance of Elements

  Try yourself:

  What is the significance of detecting elements like technetium in the spectra of certain stars?

  • A.

    It proves that these stars have reached the end of their life cycle.
  • B.

    It provides evidence for the formation of new stars.
  • C.

    It supports the theory that elements are generated within stars.
  • D.

    It helps in determining the heavy elements released during a supernova explosion.

  Explanation

  - The detection of elements like technetium in the spectra of certain stars supports the theory that elements are generated within stars.
  - This evidence suggests that stars are capable of producing heavy elements through their internal processes.
  - It further reinforces the idea that new stars are formed from enriched interstellar material, containing heavy elements released by previous stars.
  - Technetium, being a heavy element, serves as a strong indicator of stellar element production.
  - Therefore, the detection of technetium in star spectra is significant in understanding the formation and evolution of stars.

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  Introduction to Element Formation

  The majority of elements in the universe, excluding hydrogen and helium, are created within stars during their lifecycle. This fact is supported by the observation that older stars in our galaxy possess fewer heavy elements compared to younger stars.

• Stellar Element Synthesis

  Elements are synthesized within stars continuously as stars are born and die in an ongoing process.

• Population II Stars

  The oldest stars in our galaxy, known as Population II stars, originated from the initial matter of the galaxy primarily composed of hydrogen. These stars had to create their own heavy elements, leading to their relatively low abundance of heavier elements.

• Question for Cosmic Abundance of Elements

  Try yourself:

  What is the significance of detecting elements like technetium in the spectra of certain stars?

  • A.

    It proves that these stars have reached the end of their life cycle.
  • B.

    It provides evidence for the formation of new stars.
  • C.

    It supports the theory that elements are generated within stars.
  • D.

    It helps in determining the heavy elements released during a supernova explosion.

  Explanation

  - The detection of elements like technetium in the spectra of certain stars supports the theory that elements are generated within stars.
  - This evidence suggests that stars are capable of producing heavy elements through their internal processes.
  - It further reinforces the idea that new stars are formed from enriched interstellar material, containing heavy elements released by previous stars.
  - Technetium, being a heavy element, serves as a strong indicator of stellar element production.
  - Therefore, the detection of technetium in star spectra is significant in understanding the formation and evolution of stars.

  Report a problem

  Cancel Report

  View Solution

  Supernova Explosions

  Upon reaching the end of their life cycle, some of these stars explode, releasing the heavy elements they produced back into the interstellar medium.

• Formation of New Stars

  New stars are formed from this enriched interstellar material. These newer stars, referred to as Population I stars, are rich in heavy elements. They not only inherit these elements but also produce elements in their cores, serving as the building blocks for future generations of stars.

• Evidence of Stellar Element Production

  The detection of elements like technetium in the spectra of certain stars provides further support for the theory that elements are generated within stars.

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The Origin and Evolution of the Universe

Formation of Light Elements

• Only a small portion of helium in the universe was created within stars.
• Elements like hydrogen, helium, deuterium (D2), He3, and Li7 likely did not originate inside stars.
• These elements are believed to have formed within the first minute after the universe's birth.
• During this period, the universe was extremely hot and dense, providing the right conditions for the creation of light elements.
• This theory is supported by the close match between the predicted and observed abundances of light elements in the early universe.

It is fascinating to contemplate that the majority of helium that exists in the vast expanse of the universe was not actually produced within stars. Instead, fundamental elements such as hydrogen, helium, deuterium (D2), He3, and Li7 likely did not come into being through stellar processes. This intriguing theory posits that these light elements took shape within the initial sixty seconds following the universe's inception. At that precise moment, the cosmos was characterized by intense heat and density, creating the ideal environment for the genesis of these fundamental particles. The credibility of this hypothesis is bolstered by the remarkable alignment between the anticipated quantities of light elements in the ancient universe and the actual measurements we have today. This uncanny correspondence serves as compelling evidence suggesting that the early universe was a seething cauldron of extreme temperature and density, birthed in a cataclysmic event known as the Big Bang.