Origin of the Earth

Origin of the Earth

The universe is between 10 and 20 billion years old, and the common accepted age is 15 billion years. This is a very long time. To appreciate its depth, we'll map the history of the universe into one of our twelve-month calendar years. Our cosmic year begins with the formation of the universe at midnight. Although a lot goes on in the first few months, our galaxy, the Milky Way, doesn't form until May 1 and our solar system is absent until around September 9. Earth forms on September 14 and life originates in late September or early October. The Eukaryotes, the first cells with nuclei, are flourishing by mid-November but most of what we know about the history of life occurs in December.

December opens with an increase in oxygen in our atmosphere, a by product of oxygen-producing algae that destroy themselves by overproducing oxygen. The first worms appear in mid-December, and plants begin colonizing the land around December 20. Life enters middle age on Christmas and dinosaurs dominate the next few days. The first primates appear on the December 29th but the first humans don't develop until late evening on the last day of the year, near 10:30 PM. Agriculture is invented with just 40 seconds before midnight, Rome falls with three seconds remaining, and recent history makes up the last second. We are beginning the second year as newcomers to the universe.

The Big Bang

Our current, best hypothesis for the origin of the universe is called the Big Bang. The cause of the Big Bang is unknown, and so is what, if anything, went on before it. But we have learned, and are continuing to learn much about how the universe evolved since its birth. The existence of a universe-initiating explosion is supported by several lines of evidence, most notably the observed motions of the galaxies, the observed background electromagnetic hiss generated during the bang, and evidence from the observed abundance of light chemical elements in the universe.

Hubble Expansion

Observed velocities of distant supernovae measured in 1996 by Adam Reise, W. H. Press, and R. P. Kirshner. Hubble's original data only included measurements from a few Mpc distance (Mpc represents mega-parsec which is a distance equivalent to 3.24x10^6 light-years).

The slope of the line in the Hubble diagram is 63.6 kilometers per second per mega-parsec (a mega-parsec is 3.26 million light-years)

The inverse of the slope of the line in the diagram is called the Hubble age of the universe, which in this case is 15.4 billion years, near the center of the typical range of universal age estimates.

The Elements

Everything we know of is a composite of a mere 109 building blocks that we call elements. Atoms of the 92 naturally occurring elements combine to form the myriad of materials that we see and use every day. An atom is a collection of particles called protons, neutrons, and electrons (these particles are composites of still smaller particles, but we'll keep it simple). We can imagine an atom as a dense core of protons and neutrons called the nucleus, surrounded by a cloud of orbiting electrons and since protons and neutrons are much more massive than electrons, most of the mass of an atom resides in the nucleus.

Atoms are electrically balanced objects with a nucleus of protons and neutrons surrounded by a cloud of moving electrons. The charge of the nucleus, or the number of protons in the atom, uniquely identify each element. Occasionally an atom may gain or lose an electron creating a charge imbalance and producing what we call an ion.

The number of neutrons in the nucleus can vary and we call atoms of one element that have different numbers of neutrons, isotopes of that element.

The number of neutrons in an atom may also vary, producing what we call isotopes. Some isotopes of certain elements are unstable and "decay" into other isotopes or elements. We'll discuss below how these important transitions produce heat and provide natural clocks.

The periodic table is a scientific tool that helps us understand the behavior of materials. In the table, elements are ordered by the number of protons (or electrons), which we call an element's atomic number, and arranged into columns which group elements that display similar properties.

The Origin of the Elements and the Composition of the Universe

All matter in the universe was generated during the Big Bang but much of it has been reworked in the interior of stars.

Light elements were formed during the early stages of the big bang, creating a universe composed principally of hydrogen and helium. Since then, the heavier elements are manufactured by fusion processes within stars or during spectacular supernova explosions.

Our understanding of the processes that formed the solar system comes from our understanding of the physics of rotating bodies and investigation into the chemical composition of the Sun, planets, moons, and asteroids. Although much exciting work remains to be done on many aspects of solar-system evolution, we have a robust hypothesis describing the solar-system formation that provides a stable framework for research.

The solar system formed when a rotating gas cloud, the result of at least one prior supernova, was perturbed by a passing object (or another supernova) and began to collapse as a result of gravitational attraction.