Astronomy Chapter 30.1-30.4

Describe the chemical building blocks required for life

Amino acids are organic compounds that are the molecular building blocks of proteins. Proteins are key biological molecules that provide the structure and function of the body's tissues and organs and essentially carry out the "work" of the cell.

Extremophile

An organism (usually a microbe) that tolerates or even thrives under conditions that most of the life around us would consider hostile, such as very high or low temperature or acidity, is known as an extremophile

Cosmic haystack problem

Because their success depends on either guessing right about so many factors or searching through all the possibilities for each factor, some scientists have compared their quest to looking for a needle in a haystack. Thus, they like to say that the list of factors in Table 30.1 defines the cosmic haystack problem.

Explain why spaceships from extraterrestrial civilizations are unlikely to have visited us

Bernard Oliver, an engineer with an abiding interest in life elsewhere, made a revealing calculation about the costs of rapid interstellar space travel. Even with a perfect engine, the energy cost of a single round-trip journey at 70% the speed of light turns out to be equivalent to several hundred thousand years' worth of total U.S. electrical energy consumption. The cost of such travel is literally out of this world. If it's difficult for us it might be difficult for them. Given the distance and energy expense involved, it seems unlikely that the dozens of UFOs (and even UFO abductions) claimed each year could be visitors from other stars so fascinated by Earth civilization that they are willing to expend fantastically large amounts of energy or time to reach us.

Describe some of the extreme conditions on Earth, and explain how certain organisms have adapted to these conditions

Both high and low temperatures can cause a problem for life. High temperatures are the enemy of complexity—increasing thermal energy tends to break apart big molecules into smaller and smaller bits, and life needs to stabilize the molecules with stronger bonds and special proteins. high-temperature environments like hot springs and hydrothermal vents often offer abundant sources of chemical energy and therefore drive the evolution of organisms that can tolerate high temperatures (see Figure 30.8); such an organism is called a thermophile. Cold can also be a problem, in part because it slows down the metabolism to very low levels, but also because it can cause physical changes in biomolecules. Some cold-adapted cells (called psychrophiles) have changed the chemical composition of their membranes in order to cope with this problem; but again, there are limits. Conditions that are very acidic or alkaline can also be problematic for life because many of our important molecules, like proteins and DNA, are broken down under such conditions The most acid-tolerant organisms (acidophiles) are capable of living at pH values near zero—about ten million times more acidic than your blood (Figure 30.9). At the other extreme, some alkaliphiles can grow at pH levels of about 13, which is comparable to the pH of household bleach and almost a million times more alkaline than your blood. High levels of salts in the environment can also cause a problem for life because the salt blocks some cellular functions. Yet some microbes have evolved to grow in water that is saturated in sodium chloride (table salt)—about ten times as salty as seawater Very high pressures can literally squeeze life's biomolecules, causing them to adopt more compact forms that do not work very well. But we still find life—not just microbial, but even animal life—at the bottoms of our ocean trenches, where pressures are more than 1000 times atmospheric pressure.

Organic compounds

Compounds that contain carbon

DNA

DNA (deoxyribonucleic acid) that store information about how to create the cell and its chemical and structural components.

List efforts by humankind to communicate with other civilizations via messages on spacecraft

Each Pioneer carries a plaque with a pictorial message engraved on a gold-anodized aluminum plate (Figure 30.18). The Voyagers, launched in 1977, have audio and video records attached, which allowed the inclusion of over 100 photographs and a selection of music from around the world.

Identify where in the solar system life is most likely sustainable and why

Europa has probably had an ocean for most or all of its history, but habitability requires more than just liquid water. Life also requires energy, and because sunlight does not penetrate below the kilometers-thick ice crust of Europa, this would have to be chemical energy. The Galileo mission found that Europa's icy surface does contain an abundance of oxidizing chemicals. This means that availability of energy to support life depends very much on whether the chemistry of the surface and the ocean can mix, Enceladus. Plumes of gas and icy material were venting from the moon's south polar region at a collective rate of about 250 kilograms of material per second. Titan's thick atmosphere—the only one among moons in the solar system—is composed mostly of nitrogen but also of about 5% methane.

Describe some key missions and their findings in our search for life beyond our solar system

In 2005, the Cassini mission performed a close flyby of a small (500-kilometer diameter) moon of Saturn, Enceladus (Figure 30.14), and made a remarkable discovery. Plumes of gas and icy material were venting from the moon's south polar region at a collective rate of about 250 kilograms of material per second. The Galileo mission found that Europa's icy surface does contain an abundance of oxidizing chemicals. This means that availability of energy to support life depends very much on whether the chemistry of the surface and the ocean can mix, Jupiter's moon Europa revealed itself to the Voyager and Galileo missions as an active world whose icy surface apparently conceals an ocean with a depth of tens to perhaps a hundred kilometers.

Miller-Urey experiment

In a series of experiments known as the Miller-Urey experiments, pioneered by Stanley Miller and Harold Urey at the University of Chicago, biochemists have simulated conditions on early Earth and have been able to produce some of the fundamental building blocks of life, including those that form proteins and other large biological molecules known as nucleic acids

Proteins

Nutrients the body uses to build and maintain its cells and tissues

Discuss the assumption underlying the Copernican principle and outline its implications for modern-day astronomers

Philosophers of science sometimes call the idea that there is nothing special about our place in the universe the Copernican principle. Our study of astronomy has taught us that we have always been wrong in the past whenever we have claimed that Earth is somehow unique. The discovery of planets around other stars confirms our idea that the formation of planets is a natural consequence of the formation of stars. A steady stream of exoplanet discoveries is leading to the conclusion that earthlike planets occur frequently—enough that there are likely many billions of "exo-Earths" in our own Milky Way Galaxy alone. Are we a fortunate and exceedingly rare outcome of chemical evolution, or is organic biochemistry a regular part of the chemical evolution of the cosmos? We do not yet know the answer to this question, but data, even an exceedingly small amount (like finding "unrelated to us" living systems on a world like Europa), will help us arrive at it.

Pioneer plaques

Plaques placed on the pioneer that describes us to possibly communicate to extraterrestrial life if anyone were to find it.

SETI

Receivers are constantly improving, and the sensitivity of SETI programs—SETI stands for the search for extraterrestrial intelligence—is advancing rapidly.

Understand the various SETI programs scientists are undertaking

Receivers are constantly improving, and the sensitivity of SETI programs—SETI stands for the search for extraterrestrial intelligence—is advancing rapidly. If we can thus cover a broad frequency range, the cosmic haystack problem of guessing the right frequency largely goes away. For the most part, therefore, current radio SETI searches are looking for beacons, assuming that civilizations might be intentionally drawing attention to themselves or perhaps sending a message to another world or outpost that lies in our direction. Our prospects for success depend on how often civilizations arise, how long they last, and how patient they are about broadcasting their locations to the cosmos. Recently, technology has allowed astronomers to expand the search into the domain of visible light. However, in recent years, human engineers have learned how to make flashes of light brighter than the Sun. We also have the technology to detect such short pulses—not with human senses, but with special detectors that can be "tuned" to hunt automatically for such short bursts of light from nearby stars. We also have the technology to detect such short pulses—not with human senses, but with special detectors that can be "tuned" to hunt automatically for such short bursts of light from nearby stars. If we let our imaginations expand, we might think of other for technosignatures—signs of technology from other civilizations.

Voyager record

Record placed on the voyager. That has pictures and plays a sound that portrays what earth sounds like and where to find us.

Astrobiology

Scientists today take a multidisciplinary approach to studying the origin, evolution, distribution, and ultimate fate of life in the universe; this field of study is known as astrobiology. Astrobiology brings together astronomers, planetary scientists, chemists, geologists, and biologists (among others) to work on the same problems from their various perspectives.

Stromatolite

Some forms of chemical evidence contained in ancient rocks, such as the solid, layered rock formations known as stromatolites,

RNA

Some origin of life researchers believe that prebiotic chemistry was based on molecules that could both store information and do the chemical work of the cell. It has been suggested that RNA (ribonucleic acid), a molecule that aids in the flow of genetic information from DNA to proteins, might have served such a purpose.

Outline what we have learned from exploration of the environment on Mars

The earliest missions to Mars provided some hints that liquid water—one of life's primary requirements—may once have flowed on the surface, and later missions have strengthened this conclusion. T Viking's analyses of the soil said nothing about whether life may have existed in Mars' distant past, when liquid water was more abundant. Orbiting spacecraft have provided ever-more detailed images of the surface and detected the presence of minerals that could have formed only in the presence of liquid water. confirmed the existence of habitable environments on ancient Mars. Early Mars had epochs of warmer and wetter conditions that would have been conducive to life at the surface.

Describe the chemical and environmental conditions that makeEarth hospitable to life

The third planet from the Sun, as it cooled, eventually allowed the formation of large quantities of liquid water on its surface. The chemical variety and moderate conditions on Earth eventually led to the formation of molecules that could make copies of themselves (reproduce), which is essential for beginning life. mammals may owe their domination of Earth's surface to just such a collision 65 million years ago, which led to the extinction of the dinosaurs

Explain the use of biomarkers in the search for evidence of life beyond our solar system

What makes Earth "special" among the potentially habitable worlds in our solar system is that it has a photosynthetic biosphere. This requires the presence of liquid water at the planet's surface, where organisms have direct access to sunlight. The habitable zone concept focuses on this requirement for surface liquid water—even though we know that subsurface habitable conditions could prevail at more distant orbits—exactly because these worlds would have biospheres detectable at a distance. Indeed, plants and photosynthetic microorganisms are so abundant at Earth's surface that they affect the color of the light that our planet reflects out into space—we appear greener in visible wavelengths and reflect more near-infrared light than we otherwise would. When sufficiently abundant in an atmosphere, such gases could be detected by their effect on the spectrum of light that a planet emits or reflects. Astronomers have thus concluded that, at least initially, a search for life outside our solar system should focus on exoplanets that are as much like Earth as possible—roughly Earth-size planets orbiting in the habitable zone—and look for the presence of gases in the atmosphere or colors in the visible spectrum that are hard to explain except by the presence of biology.

Drake equation

an equation that lays out the factors that play a role in determining the number of communicating civilizations in our galaxy

Biomarker

an individual protein that is uniquely produced in a diseased state Second is the even more difficult task of searching for evidence of life—a biomarker—on planets circling other stars

Amino acids

building blocks of proteins

Describe the molecular systems and processes driving the origin and evolution of life

even the most primitive life required two special capabilities: a means of extracting energy from its environment, and a means of encoding and replicating information in order to make faithful copies of itself. Biologists today can see ways that either of these capabilities might have formed in a natural environment, but we are still a long way from knowing how the two came together in the first life forms. When the large impacts ceased, the scene was set for a more peaceful environment on our planet. If the oceans of Earth contained accumulated organic material from any of the sources already mentioned, the ingredients were available to make living organisms. Life as we know it employs two main molecular systems: the functional molecules known as proteins, which carry out the chemical work of the cell, and information-containing molecules of DNA photosynthesis, the complex sequence of chemical reactions through which some living things can use sunlight to manufacture products that store energy (such as carbohydrates), releasing oxygen as one by-product Some forms of chemical evidence contained in ancient rocks, such as the solid, layered rock formations known as stromatolites, are thought to be the fossils of oxygen-producing photosynthetic bacteria in rocks The rise in oxygen levels was deadly to some microbes because, as a highly reactive chemical, it can irreversibly damage some of the biomolecules that early life had developed in the absence of oxygen. For other microbes, it was a boon:

Habitable environment

habitable environment—an environment capable of hosting life—is important both for understanding how widespread habitable environments may be in the universe and for focusing a search for life beyond Earth

Describe the characteristics of a habitable environment

habitable environment—an environment capable of hosting life—is important both for understanding how widespread habitable environments may be in the universe and for focusing a search for life beyond Earth Life requires a solvent (a liquid in which chemicals can dissolve) that enables the construction of biomolecules and the interactions between them. These "biogenic elements," sometimes referred to with the acronym CHNOPS (carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur), are the raw materials from which life is assembled, and an accessible supply of them is a second requirement of habitability. You fulfill your own requirement for energy every time you eat food or take a breath, and you would not live for long if you failed to do either on a regular basis. Life on Earth makes use of two main types of energy: for you, these are the oxygen in the air you breathe and the organic molecules in your food.

Habitable zone

habitable zone—a region around a star where suitable conditions might exist for life.

Thermophile

high-temperature environments like hot springs and hydrothermal vents often offer abundant sources of chemical energy and therefore drive the evolution of organisms that can tolerate high temperatures (see Figure 30.8); such an organism is called a thermophile

Organic molecule

life on Earth is based on the presence of a key unit known as an organic molecule, a molecule that contains carbon.

Photosynthesis

photosynthesis, the complex sequence of chemical reactions through which some living things can use sunlight to manufacture products that store energy (such as carbohydrates), releasing oxygen as one by-product

Cosmic Evolution

refers to the chance origin of the universe as a whole

Interstellar travel

space flight between stars.

Understand the questions underlying the Fermi paradox

the Fermi paradox: where are they? If life and intelligence are common and have such tremendous capacity for growth, why is there not a network of galactic civilizations whose presence extends even into a "latecomer" planetary system like ours? If the Copernican principle is applied to life, then biology may be rather common among planets. Organic life around other (older) stars may have started a billion years earlier than we did on Earth, so they may have had a lot more time to develop advanced technology such as sending information, probes, or even life-forms between stars.

Fermi Paradox

the apparent contradiction between the lack of evidence and high probability estimates for the existence of extraterrestrial civilizations.

Gene

the basic functional units that carry the genetic, or hereditary, material in a cell

Copernican Principle

the principle that the Earth is not the center of the universe