READ: Where Did Elements Come From?

Where did elements come from?

Big Bang Theory – (the idea that the universe was originally extremely hot and dense at some finite time in the past and has since cooled by expanding to the present state and continues to expand) is the currently accepted theory of the early development of the universe. Cosmologists study the origin of the universe and use the term Big Bang Theory to illustrate this idea. The universe continues to expand today. The theory is supported by the most comprehensive and accurate explanations from current scientific evidence and observation.

According to the theory, the Universe would have cooled sufficiently to allow energy to be converted into subatomic particles (small parts that make up an atom). While protons (positively charged subatomic particles found on the nucleus of atoms) and neutrons –(uncharged subatomic particles that hold the nucleus together) would have formed the first atomic nuclei only a few minutes after the Big Bang, it would then have taken thousands of years for electrons (negatively charged subatomic particles that orbit the nucleus) to lose enough energy to form neutral atoms. The first element produced would be hydrogen. Giant clouds of hydrogen would then form stars and galaxies. Other elements were formed by fusion (combining small atoms together to make larger atoms) within the stars.

Evidence for the Big Bang Theory

Edwin Hubble is regarded as the leading observational cosmologist of the 1900s. He is credited with the discovery of galaxies other than the Milky Way. In 1929 Hubble presented evidence that galaxies were moving away from each other and that galaxies that are further away are moving faster, as was first suggested by a scientist named Georges Lemaître, a Belgian priest, physicist, and astronomer in 1927. Hubble’s evidence is now known as red shift –(shift of absorption bands toward the red end of the spectrum showing objects are moving further apart). This discovery was the first observational support for the Big Bang Theory. If the distance between galaxies is increasing today, then galaxies and everything else in the universe must have been closer together in the past. Think about the expanding universe, and then reverse it. If we start at the present and go back into the past, the universe gets smaller. What is the end result of a contracting universe? A point. In the very distant past, the universe must have indeed been extremely small and had extreme densities and temperatures.

The opponents to Big Bang Theory argued that if the universe had existed as a point in space, large amounts of radiation would have been produced as the subatomic particles formed from the cooling and expanding energy. After cosmic background radiation –(energy in the form of radiation leftover from the early big bang) was discovered in 1964 and the analysis matched the amount of missing radiation from the Big Bang, most scientists were fairly convinced by the evidence that some Big Bang scenario must have occurred.

In the last quarter century, large particle accelerators have been built to provide significant confirmation of the Big Bang Theory. Several particles have been discovered which support the idea that energy can be converted to particles which combine to form protons. Although these accelerators have limited capabilities when probing into such high energy regimes, significant evidence continues to support the Big Bang Theory. Recent evidence from the Wilkinson Microwave Anistropy Probe (WMAP) and Planck space probes continue to gather evidence supporting the Big Bang Theory and shows the age of the universe to be 13.8 billion years.

Elements and Big Bang Theory

If the Big Bang theory was correct, scientists predicted that they should still find most of the universe to be still composed of the hydrogen that was formed in the first few minutes after the big bang as the universe cooled and expanded. The observed abundances of hydrogen and other very light elements throughout the universe closely match the calculated predictions for the formation of these elements from the rapid expansion and cooling in the first minutes of the universe. Over 90% of the entire universe is composed of the lightest of the elements, hydrogen and helium. The heavier elements, from helium to iron were formed from fusion within stars. The same elements that the earth is made of are found throughout the universe. Fred Hoyle, who originally criticized Big Bang Theory, provided an explanation of nuclear fusion in stars as that later helped considerably in the effort to describe how heavier elements were formed from the initial hydrogen.

The earth consists of much heavier elements. The most abundant elements in the earth’s crust include oxygen, silicon, and aluminum. These elements were formed by fusion –(joining of two nuclei under high pressure and temperature) of the earliest and heaviest stars formed. The core of the earth is primarily iron. This iron was also formed is these very early, heavy stars. Nuclear fusion in stars ends at iron, as iron has the most stable nucleus. Any elements heavier than iron (such as gold, lead, etc.) must have been produced by the titanic forces of a supernova explosion. The radioactive elements found on the earth were most probably formed as these heavy stars died the violent death known as supernovae. The iron (and other elements near it on the periodic table) were thrown into the void of space with very high speeds allowing them to form still heavier elements by a similar process to which elements heavier than uranium (artificial or man-made) elements have been formed during the 20th century.

By analyzing the light given off by stars throughout the universe, scientists have been able to determine the elements that make up various objects in the universe. When we look at the light from the sun and other stars in the universe, we see the same types of spectral lines -(unique patterns of light given off by an element’s electrons) present throughout the universe. From this, we can conclude that matter exists in all stars and in our galaxy in the same general amounts. The current universe contains about 74% Hydrogen, then about 24% Helium, and 2% of the other elements. The earth, however, is composed of a greater abundance of the heavier elements. There is about 49% Oxygen, 25% Silicon, and about 7% Aluminum, with the remainder of the elements making up about 19%.

Lesson Summary

• The Big Bang Theory proposes that all matter in the universe was once contained in a small point, but has since expanded and cooled.
  
• The theory is supported by scientists as it provides a satisfactory explanation for the observations that the universe is expanding today, that the universe is composed mostly of hydrogen and helium, cosmic background radiation, etc.
  
• The theory also provides as explanation for where elements heavier than hydrogen were formed, through fusion into heavier elements.

CC-BY-NC-SA Utah State Office of Education. Material adapted from ck12.org

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