Stanley Miller and Harold Urey put these ideas to the test by synthesizing amino acids in the lab under presumed primitive Earth conditions. Some physicists and astronomers were convinced that the abundance of habitable zones in the Milky Way ensured the possibility of many biological experiments. If that was the case, it might be worth looking for advanced civilizations directly.
In , the young Frank Drake, a newly minted Harvard Ph. During the great era of planetary exploration in the s, the agency administrated a small grants program for research related to life in the universe. Federal funding for this initiative exceeds one hundred million dollars per year. NASA cut astrobiology by 50 percent in to pay for the Moon, Mars, and Beyond initiative, and a cloud hangs over future promising missions.
The United States the living cosmos 49 Figure NASA is the principal funding agency for the interdisciplinary community of researchers seeking answers to these questions. Astrobiology is compelling not just because it seeks to answer big questions but because it encourages scientists to think outside the box. Astronomers get to imagine all the places in the universe that might be habitable.
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Planetary scientists look at the ways life might alter a planetary surface or atmosphere. Biologists muse on the possibility of life without DNA or carbon. At biannual conferences hosted by the NASA Astrobiology Institute, cosmologists rub shoulders with geneticists and philosophers. Interdisciplinary research goes against the grain of modern science, which has become increasingly specialized.
The palpable 50 chris impey excitement of astrobiology stems in part from scientists venturing out of the safe harbors of their own disciplines and creating new bodies of knowledge. The continuing Copernican Revolution supports the expectation of life beyond Earth by showing that the basic ingredients—carbon, water, planets, and stars—are widespread in the universe. As a prelude to speculating about the potential for life in the universe, we must learn as much as we can from the only known living planet. In this area, all is conjecture.
Volcanoes belch gases into the sky, and the spacecraft trembles every few minutes from seismic activity. A young star, orange and bloated, perches on the horizon. The newly minted crust is still warm and plastic. Oceans have recently condensed from steam and are still kept warm and turgid by geothermal energy.
Location, location, location
Samples drilled from the crust show an age of two hundred million years—only 2 percent of cosmic time and the same fraction of the time the star will provide warmth to this planet. Working swiftly, the visitors wrap up their experiments. This soon after its formation, the planetary system is still strewn with debris. Every hour or so, the spacecraft shudders as a meteor slams into the ground nearby. The large moon looming in the sky, which was splashed off an earlier impact, is a reminder of the potential for devastation.
Equipped with biosensors, they have fanned out across the landscape and the seascape. They found nothing larger than a sand grain, but the results are all consistent. Life grips this young planet like a fever. Elements trapped inside it reveal what the Earth was like not long after it formed. As far as we know, the fundamental building blocks of life are carbon, nitrogen, oxygen, and hydrogen. The last two combine to make water, which is essential for all life on Earth. Why is star stuff so different from life stuff?
To answer this question, we must venture into stellar and cosmic cataclysms that took place long before the Sun and Earth formed. Scientists use the decay of the nuclei of atoms to measure the age of ancient things, so telling the story of life on Earth requires a detour into the physics of radioactivity.
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Only then can we begin to learn from the zircon. Tracing the history of life becomes possible when we can date rocks. They still have no reliable answer to a central question: how did simple molecules assemble themselves into long replicating chains and then cells? They also know little about the early experimentation that left all current living organisms with a single genetic code based on the DNA molecule. Regardless of how and when life started, natural selection has sculpted it into an amazing variety of forms.
Geology and biology on our planet are coupled in a profound and complex way, as we see when we consider the Gaia hypothesis. Who are the travelers in the opening vignette? They might be our future selves, once we have mastered space technology and begin to search the nearest star systems for inhabited planets. But the same scene would have greeted aliens of unfamiliar function and form who ventured into our Solar System when it was young. They would have found the Earth to be a watery world rich in organic material, with primitive life full of promise and potential. The universe is mostly dead and inert.
On the other hand, a typical living organism is 40 percent carbon, nitrogen, and oxygen. Those three elements plus about a dozen trace elements on which life depends combine to give the richness of organic chemistry. The origin of life begins with the birth of its chemical ingredients. The universe today is old and cold, with its stars and galaxies spread across billions of light-years of almost perfectly empty space.
But long ago, your atoms and my atoms and the atoms of all the creatures on Earth were joined in a titanic event of unimaginable power called the big bang. All life in the universe shares the kinship of a birth Very early in the expansion, when the universe was ten seconds old and a 54 chris impey billion times smaller than it is now, collisions between protons were violent enough that some of them stuck together. In a large-scale version of the same process that causes the Sun to shine, hydrogen was converted into helium.
One-quarter of the mass of the universe had been converted into helium. If we ask what the universe is made of, the answer is shown in Figure The plot shows the cosmic abundance of elements across the periodic table, from hydrogen to uranium. There are ten times as many hydrogen atoms as helium atoms. Hydrogen is thousands of times more common than the life elements C, N, O , millions of times more common than aluminum or copper, and billions of times more common than gold or silver.
Apart from hydrogen, everything else is a trace element. Just how rare? Suppose a deck of cards represented randomly selected atoms in the universe.
The Living Cosmos Our Search For Life In Universe Chris Impey
In one deck of cards, the aces would be helium atoms and the other forty-eight would be hydrogen atoms. If those cards were in direct proportion to the elements of the universe, there would be only one gold atom in the entire cube. Astronomers use remote sensing by spectroscopy to measure the composition of star stuff. At its heart was the dream of turning a base metal like lead into a precious metal Figure The cosmic abundance of the elements in the like gold.
The vertical scale is logarithmic, which geous; both are dense, malleable allows heavier elements to be visible; they are all metals of dull appearance in incredibly rare. The life elements—carbon, nitrogen, and oxygen—have concentrations of a few parts in ten their natural state. Alchemy was thousand relative to hydrogen, and elements heavier than protoscience rather than crank zirconium have concentrations less than one part in a science, and its imagery has billion. Alchemy features in the titles of two of the books, the symbolism in the naming of many of the characters, and in the person of Hogwarts headmaster Albus Dumbledore, who is stated to be an alchemist of renown, partner of Nicolas Flamel, a real-life alchemist from the fourteenth century.
In real life, however, alchemy was doomed to failure.
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The essence of an element lies in its atomic nucleus, and this fortress cannot be touched by chemical means, which operate only on the outer shell of electrons. Every star is involved in the transmutation of elements. Because stars are large gas balls held together by gravity, the density and temperature rise smoothly as you move toward their centers.
In the interior of the Sun, where the temperature exceeds ten million degrees, hydrogen is converted into helium by the process of fusion, which is the merging of atomic nuclei to form 56 chris impey heavier elements. The protons in atomic nuclei have a positive electric charge, so they resist one another like tiny magnets. It requires a phenomenal temperature to force them to fuse. The energy released from the nuclear reactions reaches us as sunlight. A typical star like the Sun spends most of its life fusing hydrogen into helium. After the hydrogen is exhausted, the star loses its pressure support, and its core collapses.
That compression continues until the ignition of a new nuclear fuel creates a balance at a new, higher temperature. Fusion is an unnatural act: it forces atomic nuclei to merge. The helium nucleus has two protons, so its positive electrical charge is larger than that of hydrogen, which has only one.
The electrical repulsion is four times larger and it takes a temperature of one hundred million degrees to make helium fuse. The next step is the key to life. Two helium nuclei fuse to make a beryllium nucleus, but beryllium is unstable, and it decays in a tiny fraction of a second. Occasionally, some beryllium survives, and if the energy levels are just right a third helium nucleus is added. Carbon is born. This two-step fusion is so tricky that it causes a bottleneck. As a result, the universe has three hundred times less carbon than helium. Now it gets interesting.
Add a hydrogen nucleus, and the atomic number increases by one. Add a helium nucleus, and it increases by two. But in higher-mass stars, when an extra proton is added to carbon, it becomes nitrogen. One more and oxygen is formed. Suitably warmed up, the cosmic element maker picks up the pace. Helium fused to oxygen makes neon. Helium fused to neon makes magnesium.