CHAPTER 1
ORIGINS: A CHEMICAL HISTORY OF THE EARTH FROM THE BIG BANG UNTIL NOW-13.8 BILLION YEARS OF REVIEW

Not only is the Universe stranger than we imagine, it is stranger than we can imagine.

-Sir Arthur Eddington

I'm astounded by people who want to 'know' the universe when it's hard enough to find your way around Chinatown.

-Woody Allen

1.1 INTRODUCTION

Georges-Henri LemaÎtre (1894-1966), a Jesuit priest and physicist at Université Catholique de Louvain, was the first person to propose the idea of the Big Bang. This theory describes the birth of our universe as starting from a massive, single point in space at the beginning of time (literally, = 0 s!), which began to expand in a manner that could loosely be called an explosion. Another famous astrophysicist and skeptic of LemaÎtre's hypothesis, Sir Fred Hoyle (1915-2001), jeeringly called this the "Big Bang" hypothesis. Years later, with several key experimental predictions having been observed, the Big Bang is now a theory. LemaÎtre developed his hypothesis from solutions to Albert Einstein's (1879-1955) theory of general relativity. Since this is not a mathematics book, and I suspect you are not interested in tackling the derivation of these equations (neither am I), so let us examine the origin of our environment and the conditions that led to the Earth that we inhabit. This chapter is not meant to be a rigorous and exhaustive explication of the Big Bang and the evidence for the evolution of the universe, which would require a deep background in atomic particle physics and cosmology. Since this is an environmental chemistry text, I will only describe items that are relevant for the environment in the context of a review of general chemistry.

1.2 THE BIG BANG

1.2.1 The Microwave Background

The first confirmation of the Big Bang comes from the prediction and measurement of what is known as the microwave background. Imagine you are in your kitchen and you turn on an electric stove. If you placed your hand over the burner element, you would feel it heat up. This feeling of heat is a combination of the convection of hot air touching your skin and infrared radiation. As the heating element warms up, you would notice the color of it changes from a dull red to a bright orange color. If it could get hotter, it would eventually look whitish because it is emitting most of the colors of the visible spectrum. What you have observed is Wien's Displacement Law, which describes blackbody radiation.

1.1

This equation shows how the temperature (T) of some black object (black so that the color of the object is not mistaken as the reflected light that gives an apple, e.g., its red or green color) affects the radiation () the object emits. On a microscopic level, the emission of radiation is caused by electrons absorbing the heat of the object and converting this energy to light.

The in Wien's equation represents, roughly, the average wavelength of a spectrum, such as in Figure 1.1, which shows the emission spectrum of the Sun. Wien's Law also lets us predict the temperature of different objects, such as stars, by calculating T from .

Figure 1.1 Another view of the solar radiation spectrum showing the difference between the radiation at the top of the atmosphere and at the surface. Source: Robert A. Rhode http://en.wikipedia.org/wiki/File:Solar_Spectrum.png. Used under BY-SA 3.0 //creative commons.org/licenses/by-sa/3.0/deed.en

Robert Dicke (1916-1977), a physicist at Princeton University, predicted that if the universe started out as a very small, very hot ball of matter (as described by the Big Bang) it would cool as it expanded. As it cooled, the radiation it would emit would change according to Wien's Law. He predicted that the temperature at which the developing universe would become transparent to light would be when the temperature dropped below 3000 K. Given that the universe has expanded a 1000 times since then, the radiation would appear red-shifted by a factor of 1000, so it should appear to be 3 K. How well does this compare to the observed temperature of the universe?

For a review of the EM spectrum, see Review Example 1.1 on page 22.

When looking into the night sky, we are actually looking at the leftovers of the Big Bang, so we should be seeing the color of the universe as a result of its temperature. Since the night sky is black except for the light from stars, the background radiation from the Big Bang must not be in the visible region of the spectrum but in lower regions such as the infrared or the microwave region. When scientists at Bell Laboratories in New Jersey used a large ground-based antenna to study emission from our Milky Way galaxy in 1962, they observed a background noise that they could not eliminate no matter which direction they pointed the antenna. They also found a lot of bird poop on the equipment, but clearing that out did not eliminate the "noise." They finally determined that the noise was the background emission from the Big Bang, and it was in the microwave region of the EM spectrum (Table 1.1), just as Dicke predicted. The spectral temperature was measured to be 2.725 K. This experimental result was a major confirmation of the Big Bang Theory.

Table 1.1 Certain regions of the electromagnetic (EM) spectrum provide particular information about matter when absorbed or emitted

Gamma rays: Excites energy levels of the nucleus; sterilizing medical equipment X-Rays: Refracts from the spaces between atoms and excites core ; provides information on crystal structure; used in medical testing Ultraviolet: Excites and breaks molecular bonds; polymerizing dental fillings Visible: Excites atomic and molecular electronic transitions; our vision Infrared: Excites molecular vibrations; night vision goggles Microwave: Excites molecular rotations; microwave ovens Radio waves: Excites nuclear spins; MRI imaging and radio transmission

Blackbody Radiation

The electric heater element (Figure 1.2) demonstrates blackbody radiation. Any object that has a temperature above 0 K will express its temperature by emitting radiation that is proportional to its temperature. Wien's Displacement Law gives the relationship between the average wavelength of the radiation and the temperature. The Earth emits infrared radiation as a result of its temperature, and this leads to the greenhouse effect, which is discussed later. The person in the photos in Figure 1.3 also emits radiation in the infrared, allowing an image of his arm and hand to be seen despite the visible opacity of the plastic bag.

Figure 1.2 A glowing electric stove element. Courtesy K. Overway.

Figure 1.3 While visible radiation cannot penetrate the plastic bag, the infrared radiation, generated by the blackbody radiation of the man's body, can. Source: NASA.

Infrared Thermography

Infrared thermography is an application of Wien's Law and is a key component of a home energy audit. One of the most cost-effective ways to conserve energy is to improve the insulation envelope of one's house. Handheld infrared cameras, seen in Figure 1.4, allow homeowners or audit professionals to see air leaks around windows and doors. On a cold day, an uninsulated electrical outlet or poorly insulated exterior wall could be 5-8 F colder than the surroundings. When the handheld thermal camera is pointed at a leak, the image that appears on the screen will clearly identify it by a color contrast comparison with the area around it.

Figure 1.4 A thermal camera used to find cold spots in a leaky house. Source: Passivhaus Institut "http://en.wikipedia.org/wiki/File:SONEL_KT-384.jpg" Used under BY- SA 3.0 //creativecommons.org/licenses/by-sa/3.0/deed.en.

Example 1.1: Blackbody Radiation

Wien's Displacement Law is an important tool for determining the temperature of objects based on the EM radiation that they emit and predicting the emission profile based on the temperature of an object.

1. Using Wien's Displacement Law (Eq. (1.1)), calculate the for a blackbody at 3000 K.
2. Using Wien's Displacement Law, calculate the for the Earth, which has an average surface temperature of 60 F.
3. In which portion of the EM spectrum is the for the Earth?

Solution

See Section A.1 on page 231.

After the development of modern land-based and satellite telescopes, scientists observed that there were other galaxies in the universe besides our own Milky Way. Since this is true, the universe did not expand uniformly - with some clustering of matter in some places and very little matter in others. Given what we know of gravity, the clusters of matter would not expand at the same rate as matter that is more diffuse. Therefore, there must be some hot and cold spots in the universe, and the microwave background should show this. In 1989, an advanced microwave antenna was launched into space to measure this predicted heterogeneity of temperature. Further...