Origin of the Elements

The Creation of the Universe There are many theories of how the universe was created. One theory developed by Einstein, Hoyle, and others is called the “Steady State Theory.” The current and most popular theory of the creation of our universe is called the “Big Bang Theory.” The Big Bang Theory states that the universe formed about 14 billion years ago and has been expanding ever since. All theories show that matter was formed at a very early stage in the history of our universe.

In the Beginning - Gas The first elements to form in our universe were hydrogen and deuterium, both gases. Hydrogen has one proton and one electron: 1 H Deuterium is an isotope of hydrogen. It has one proton, one electron, and one neutron: 2 D

How is Deuterium Formed? Deuterium is formed when hydrogen atoms disintegrate into protons, which break down into a neutron and a positron, a positively charged electron: + - + Protons, neutrons and electrons are the basic parts of atoms that are used to create all the other elements in the periodic table.

Deuterium Formation Protons fuse with neutrons and add electrons to form deuterium:

The gases combine to form stars Gravity caused the gases to condense into clumps of atoms at very high pressures that formed the first stars. These stars were hundreds of times larger than our Sun. Deep within the center of these gigantic stars the temperature reached hundreds of thousands or even millions of degrees Celsius. These high temperatures and pressures caused the hydrogen and deuterium to form helium in a process called nuclear fusion, which is sometimes unfortunately called “burning” although it is not combustion.

Nuclear Fusion – the First Steps Two deuterium atoms can fuse to form helium: 4 He

Nuclear Fusion Continues Gamma rays, electrons and photons as well as sub-atomic particles called neutrinos and positrons are produced under the extreme conditions in stars. Source: Sky & Telescope, March 2008, 26

Nuclear Fusion Inside the Stars The extremely high temperatures and pressures generated by nuclear fusion causes helium nuclei, also known as alpha particles, to be converted into elements with larger and larger masses. The so-called Triple Alpha Process shows how helium is converted into beryllium and carbon during this burning process.

Source: Sky & Telescope, March 2008, 26

Nuclear Fusion – The Elements of Life Once carbon, the first key element of life, is formed, the other life supporting elements, oxygen and nitrogen, are formed in what is called the CNO Cycle. Source: Sky & Telescope, March 2008, 26

Evolution of Stars Stage 1 - When the star is first formed only helium (He) is formed at the core. Stage 2 - After the hydrogen is used up in the core, the helium begins fusing into carbon (C) at its core, but hydrogen continues to form helium in a thin layer farther out. Stage 3 – the star swells to become a “red giant” and the smaller elements fuse to former larger and larger elements.

Stage 1 Stage 2 Stage 3 Red Giant Source: Sky & Telescope, March 2008, 26

Evolution of Stars Stage 4 – Elements such as sodium (Na), neon (Ne), magnesium (Mg), oxygen (O), sulfur (S), and silicon (Si) are formed in the outer layers. The heavier elements are formed closer to the core and eventually fuse in the core of the star to form iron (Fe), the most massive element found in stars.

Stage 4 Source: Sky & Telescope, March 2008, 26

Forming Heavier Elements in Supernova After a star reaches its maximum stage in several billion years, a massive explosion called a “Supernova” will blow the star apart. The extreme temperatures that occur during this explosion, are estimated to be more than 100 million degrees Celsius. This enables atoms and neutrons to be released at an enormous rate.

The Crab Nebula – Remains of a Supernova Explosion Source: Sky & Telescope, March 2008, 32

Forming Heavier Elements in Supernova Neutrons are captured by atoms to form more massive elements. Source: Sky & Telescope, March 2008, 32

Forming Heavier Elements in Supernova When an atom captures a neutron, it becomes a heavier isotope of the same atom. In unstable isotopes, a neutron decays into a proton, electron and neutrino, converting the atoms into the next element in the periodic table. The process continues until all the heavier elements are produced.

How did the elements reach Earth? When stars and supernova explode, they send burning pieces of mass in all directions. These hot masses, which contain the elements, spread throughout the universe to eventually form other stars and planets. Our solar system was created in this way over a period of many billions of years.

A Planetary Nebula – Remains of an Exploding Star NGC5315 7,000 light years away Source: Sky & Telescope, March 2008, 32

Bibliography Beers, Timothy C., “Origin of the Elements of Life,” Sky & Telescope, March 2008, 26. James, C. Renee, “Where Did You Come From?” Sky & Telescope, March 2008, 32. Ziurys, Lucy M., “The Chemistry in Circumstellar Envelopes of Evolved Stars,” Proc. of Nat’l Acad. of Sciences, 103, (33) 12274 (2006).