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Mar 3, 2018 · Still today, many people believe that we, humankind, are the creation of a supernatural entity called God, ... If it is the brevity or finiteness of human life that gives it shape and purpose (an ...
- What Is Life
The agency’s working definition is a pretty good one: “Life...
- What Is Life
Oct 2, 2023 · An answer (as opposed to The Answer) to The Ultimate Question is that we exist to continue to exist. We evolved to evolve. This is fundamental to every living organism. Inherent to our existence ...
- Sarah Crow
- Contributor
- Working no longer means heading into an office. If you said you were "going to work" fifty years ago, that meant heading to a physical location outside of your home and chugging away until 5.
- Exercise isn't just for fitness fanatics anymore. While it's not exactly like jogging or playing sports was invented in the last 50 years, the global focus on fitness has undeniably increased in the past half-century.
- Virtually nobody has a home phone. 50 years ago, a home phone was a necessity. The number of people using one today, however, is lower than ever. In fact, according to CDC data, less than 50 percent of American homes now have a landline, with most opting for cell service instead.
- We interact completely differently. Back in the 1960s, if you wanted to get in touch with a friend, you rang them up on said land-line phone and asked how they were doing.
- Overview
- Definitions of life
- Metabolic
- Physiological
- Biochemical
life, living matter and, as such, matter that shows certain attributes that include responsiveness, growth, metabolism, energy transformation, and reproduction. Although a noun, as with other defined entities, the word life might be better cast as a verb to reflect its essential status as a process. Life comprises individuals, living beings, assignable to groups (taxa). Each individual is composed of one or more minimal living units, called cells, and is capable of transformation of carbon-based and other compounds (metabolism), growth, and participation in reproductive acts. Life-forms present on Earth today have evolved from ancient common ancestors through the generation of hereditary variation and natural selection. Although some studies state that life may have begun as early as 4.1 billion years ago, it can be traced to fossils dated to 3.5–3.7 billion years ago, which is still only slightly younger than Earth, which gravitationally accreted into a planet about 4.5 billion years ago. But this is life as a whole. More than 99.9 percent of species that have ever lived are extinct. The several branches of science that reveal the common historical, functional, and chemical basis of the evolution of all life include electron microscopy, genetics, paleobiology (including paleontology), and molecular biology.
The phenomenon of life can be approached in several ways: life as it is known and studied on planet Earth; life imaginable in principle; and life, by hypothesis, that might exist elsewhere in the universe (see extraterrestrial life). As far as is known, life exists only on Earth. Most life-forms reside in a thin sphere that extends about 23 km (14 miles) from 3 km (2 miles) beneath the bottom of the ocean to the top of the troposphere (lower atmosphere); the relative thickness is comparable to a coat of paint on a rubber ball. An estimated 10–30 million distinguishable species currently inhabit this sphere of life, or biosphere.
Much is known about life from points of view reflected in the various biological, or “life,” sciences. These include anatomy (the study of form at the visible level), ultrastructure (the study of form at the microscopic level), physiology (the study of function), molecular biology and biochemistry (the study of form and function at chemical levels)...
Metabolic definitions are popular with biochemists and some biologists. Living systems are objects with definite boundaries, continually exchanging some materials with their surroundings but without altering their general properties, at least over some period of time. However, there are exceptions. There are frozen seeds and spores that remain, so far as is known, perfectly dormant. At low temperatures they lack metabolic activity for hundreds, perhaps thousands, of years but revive perfectly well upon being subjected to more clement conditions. A candle flame has a well-defined shape with a fixed boundary and is maintained by “metabolizing” its organic waxes and the surrounding molecular oxygen to produce carbon dioxide and water. Similar reactions, incidentally, occur in animals and plants. Flames also have a well-known capacity for growth. These facts underscore the inadequacy of this metabolic definition, even as they suggest the indispensable role of energy transformation to living systems. (See metabolism.)
Britannica Quiz
Physiological definitions of life are popular. Life is defined as any system capable of performing functions such as eating, metabolizing, excreting, breathing, moving, growing, reproducing, and responding to external stimuli. But many such properties are either present in machines that nobody is willing to call alive or absent from organisms, such...
A biochemical or molecular biological definition sees living organisms as systems that contain reproducible hereditary information coded in nucleic acid molecules and that metabolize by controlling the rate of chemical reactions using the proteinaceous catalysts known as enzymes. In many respects, this is more satisfying than the physiological or metabolic definitions of life. However, even here there are counterexamples. Viruslike agents called prions lack nucleic acids, although the nucleic acids of the animal cells in which they reside may be involved in their reproduction. Ribonucleic acid (RNA) molecules may replicate, mutate, and then replicate their mutations in test tubes, although by themselves they are not alive. Furthermore, a definition strictly in chemical terms seems peculiarly vulnerable. It implies that, were a person able to construct a system that had all the functional properties of life, it would still not be alive if it lacked the molecules that earthly biologists are fond of—and made of. (See biochemistry.)
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Life is neither fixed nor absolute, it is ambiguous; life is the possibilities entailed by existence. Life is the consciousness of humanity; it is perception of the world and the universe. So life is sadness; life is death. Life is suffering and destruction. But life is also happiness; life is living.
Sep 27, 2019 · The agency’s working definition is a pretty good one: “Life is a self-sustaining chemical system capable of Darwinian evolution.”. Nice, but far from perfect. Few if any species are “self ...
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May 15, 2007 · 3. Naturalism. Recall that naturalism is the view that a physical life is central to life’s meaning, that even if there is no spiritual realm, a substantially meaningful life is possible. Like supernaturalism, contemporary naturalism admits of two distinguishable variants, moderate and extreme (Metz 2019).
