Entire courses and careers have been based on wide-ranging topics covering Earth’s history. Throughout Earth’s long history, change has been the norm. Looking back in time, the untrained eye will see many unfamiliar life forms and terrain. The main subjects studied in Earth history are paleogeography, paleontology, paleobiology, and paleoclimatology—respectively, past landscapes, past organisms, past ecosystems, and past environments. This chapter will cover (briefly) the origin of the universe and the 4.6 billion year history of the Earth. It will serve as a guide linking other chapters, case studies, and sections in this book.
the origin of the universe
A deep field of grief. This image, published in 1996, is a long exposure composite image of one of the darkest parts of the night sky. Not every light in this image is considered to have the diffraction heights of an entire galaxy, with hundreds of billions of stars, indicating the massive size and scope of the universe.
The universe seems to contain an infinite number of galaxies and solar systems and our solar system occupies a small part of this vast complex. The origins of the universe and the solar system set the context for the concept of the earth’s origin and early history.
the big Bang
The mysterious details of events before and during the emergence of the universe are subject to great scientific debate. The dominant idea of how the universe was created is called the big bang theory. Although the ideas behind the big bang theory seem almost mysterious, it is supported by Einstein’s theory of general relativity. Other scientific evidence, based on experimental observations, supports the Big Bang theory.
The Big Bang theory proposes that the universe was formed from a dense and very hot nucleus of matter. The explosion in the title indicates an explosive outward expansion of all matter and space resulting in the formation of atoms. Spectroscopy confirms that hydrogen makes up about 74% of all matter in the universe. Since its inception, the universe has been expanding for 13.8 billion years, and recent observations indicate that this rate of expansion is increasing.
Electromagnetic spectrum and the properties of light across the spectrum.
Spectroscopy is the examination and measurement of the spectrum produced when substances interact with or emit electromagnetic radiation. Spectra is the plural form of spectrum which is a specific wavelength of the electromagnetic spectrum. Common spectra include the various colors of visible light, X-rays, ultraviolet, microwaves, and radio waves. Each beam of light is a unique combination of wavelengths that combine across the spectrum to create the color we see. Wavelengths of light are created or absorbed within atoms, and each wavelength signature corresponds to a particular element. Even white light from the sun, which appears to be a continuum of wavelengths, has gaps in certain wavelengths. Gaps correspond to elements in Earth’s atmosphere that act as filters for specific wavelengths. Joseph von Fraunhofer (1826-1787) was best known for observing these missing wavelengths in the early 1800s, but it was decades before scientists were able to correlate the missing wavelengths with atmospheric filtering. Spectroscopy shows that the Sun is composed mostly of hydrogen and helium. By applying this process to light from distant stars, scientists can calculate the abundance of elements in a particular star and the visible universe as a whole. Also, this spectroscopic information can be used as an interstellar accelerometer.
The Doppler effect is the same process that changes the tone of an approaching car or ambulance from high to low as it passes. When an object emits waves, such as light or sound, while moving towards an observer, the wavelengths are compressed. In sound, this causes a transition to a higher pitch. As an object moves away from the viewer, the wavelengths are stretched, resulting in a low-pitched sound. The Doppler effect is used on the light emitted by stars and galaxies to determine their speed and direction of travel. Scientists, including Pesto Sliver (1875–1969) and Edwin Hubble (1889–1953), have examined both nearby and distant galaxies and found that nearly all galaxies outside our galaxy are moving away from each other and from it. As the wavelengths of light from receding objects expand, the visible light is shifted toward the red end of the spectrum, called redshift. In addition, Hubble saw that galaxies that were further away from Earth also had a greater redshift, and therefore, the faster they were moving away from us. The only way to reconcile this information is to conclude that the universe is still expanding. Hubble’s observation forms the basis of the Big Bang theory.
Cosmic microwave background radiation
Another strong indicator of the Big Bang is the cosmic microwave background radiation. Cosmic radiation was accidentally discovered by Arno Panzias (1933-) and Robert Woodrow Wilson (1936-) when they were trying to remove background noise from a communications satellite. They discovered very faint traces of energy or heat scattered throughout the universe. This energy is left over from the big bang, like an echo.
Evolution of stars
The origin of the elements in the periodic table, showing the important role played by the life cycle of a star.
Astronomers believe that the Big Bang created lighter elements, mainly hydrogen and smaller amounts of the elements helium, lithium and beryllium. Another process should be responsible for creating the 90 heavier items. The current model of stellar evolution explains the origins of these heavy elements.
Stars begin their lives as elements floating in cold clouds of gas and dust surrounding nebulae. Gravitational pull or perhaps a nearby starburst causes the elements to condense and swirl in the disk. In the center of this disk, a new star is born under the influence of gravity. The spinning vortex concentrates the matter in the center, and the increasing gravitational forces collect more mass. Eventually, the mass of the highly concentrated material reaches a critical point from this intense heat and pressure that initiates fusion. Fusion is not a chemical reaction. Fusion is a nuclear reaction in which two or more nuclei, the centers of atoms, are forced together to form a new, larger atom. This reaction produces a huge amount of energy, usually in the form of light and solar radiation. An element like hydrogen combines or fuses with other hydrogen atoms in the star’s core to become a new element, in this case, helium. Another product of this process is energy, such as solar radiation that leaves the sun and reaches the earth in the form of light and heat. Fusion is a regular and predictable process, which is why we call it the main stage in a star’s life. In its main phase, the star turns hydrogen into helium. Because most stars contain large amounts of hydrogen, the main phase may last for billions of years, during which its size and energy production remain relatively constant.
The giant stage in a star’s life occurs when the star runs out of hydrogen for fusion. If a star is big enough, it has enough heat and pressure to start fusing helium into heavier elements. This mode of fusion is more active and as the energy and temperature increase, the star expands to greater size and brightness. This giant phase of our sun is expected to occur within a few billion years, increasing the radius of the sun to orbit the earth, making life impossible. The mass of a star in its primary phase is the main factor in determining how it evolves. If the star has enough mass and reaches the point where the primary fusion element, such as helium, is depleted, fusion continues using new, heavier elements. This happens over and over again in very large stars, resulting in heavier and heavier elements like carbon and oxygen. Eventually, fusion reaches a limit because it is composed of iron and nickel. This progression explains the abundance of iron and nickel in rocky bodies, such as Earth, within the solar system. At this point, any further fusion absorbs energy instead of giving it, and this is the beginning of the end of the star’s life.