Life Definition and 1000 Threads

Life is a characteristic that distinguishes physical entities that have biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased (they have died), or because they never had such functions and are classified as inanimate. Various forms of life exist, such as plants, animals, fungi, protists, archaea, and bacteria. Biology is the science that studies life.

There is currently no consensus regarding the definition of life. One popular definition is that organisms are open systems that maintain homeostasis, are composed of cells, have a life cycle, undergo metabolism, can grow, adapt to their environment, respond to stimuli, reproduce and evolve. Other definitions sometimes include non-cellular life forms such as viruses and viroids.
Abiogenesis is the natural process of life arising from non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to living entities was not a single event, but a gradual process of increasing complexity. Life on Earth first appeared as early as 4.28 billion years ago, soon after ocean formation 4.41 billion years ago, and not long after the formation of the Earth 4.54 billion years ago. The earliest known life forms are microfossils of bacteria. Life on Earth is probably descended from an RNA world, although RNA-based life may not have been the first life to have existed. The classic 1952 Miller–Urey experiment and similar research demonstrated that most amino acids, the chemical constituents of the proteins used in all living organisms, can be synthesized from inorganic compounds under conditions intended to replicate those of the early Earth. Complex organic molecules occur in the Solar System and in interstellar space, and these molecules may have provided starting material for the development of life on Earth.Since its primordial beginnings, life on Earth has changed its environment on a geologic time scale, but it has also adapted to survive in most ecosystems and conditions. Some microorganisms, called extremophiles, thrive in physically or geochemically extreme environments that are detrimental to most other life on Earth. The cell is considered the structural and functional unit of life. There are two kinds of cells, prokaryotic and eukaryotic, both of which consist of cytoplasm enclosed within a membrane and contain many biomolecules such as proteins and nucleic acids. Cells reproduce through a process of cell division, in which the parent cell divides into two or more daughter cells.
In the past, there have been many attempts to define what is meant by "life" through obsolete concepts such as odic force, hylomorphism, spontaneous generation and vitalism, that have now been disproved by biological discoveries. Aristotle is considered to be the first person to classify organisms. Later, Carl Linnaeus introduced his system of binomial nomenclature for the classification of species. Eventually new groups and categories of life were discovered, such as cells and microorganisms, forcing dramatic revisions of the structure of relationships between living organisms. Though currently only known on Earth, life need not be restricted to it, and many scientists speculate in the existence of extraterrestrial life. Artificial life is a computer simulation or human-made reconstruction of any aspect of life, which is often used to examine systems related to natural life.
Death is the permanent termination of all biological processes which sustain an organism, and as such, is the end of its life. Extinction is the term describing the dying out of a group or taxon, usually a species. Fossils are the preserved remains or traces of organisms.

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  1. T

    Calculating Steel Rod Life with 8000 psi at 1000 °F

    1. Problem statement A steel rod supporting a stress of 8000 psi at 1000 ◦ F is not to exceed 5 % creep strain. Knowing that the steady-state creep rate can be expressed by an equation of the form ##\dot{\epsilon}_{s}^{C}=B|\sigma |^{n} exp \left(\frac{-Q}{kT} \right)## ε⋅, strain rate B...
  2. G

    Laws of thermodynamics compared with life.

    Dear friends! I had read about a comparison of laws of thermodynamics as follows. " If energy extraction is a game. First law: You cannot win the game. Second law: There is no break even. Third law:You can not leave the game". My problem is that I cannot convincingly understand the comparison...
  3. Chemer

    Thermodynamics and daily life

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  4. A

    Graduate specialization; synergy in life science

    I am a undergraduate in an interdisciplinary life science/biochem/mol.bio/physical.chem degree thinking about which optionals to take. For this I have to consider what specialization I want to pick in my major. The two I am leaning towards are biophysics and biochem. There is also medical...
  5. E

    Programs Graduate Advice for Achieving a First in UK Physics Degree

    I started my undergraduate physics degree in September, and having been enjoying it a lot so far. As I'm sure any student does - I am aiming for a First. I was wondering if any graduates would be able to help me out by answering a few questions for me on their experience: Are there any things...
  6. TheNerdConstant

    What's the best ways to balance study/social life?

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  7. M

    How Does the Two Slit Experiment Illustrate Quantum Duality?

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  8. A

    High school years are the best years of your life

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  9. N

    How do you all cope with the futility of life

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  10. P

    Does battery life decrease as current increases?

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  11. S

    What Can I Do After College with My Diverse Interests?

    I know, the most dramatic and trite question. I am currently a junior physics and math major. Physics is my primary major, and I am considering an honors degree. I have to write a senior thesis, so I have been research-shopping: I dabbled in particle physics (computational data analysis of the...
  12. ShayanJ

    A simulation for finding the origings of life

    I remember, a year or two ago, reading about a group which were simulating the early times of Earth's creation and they wanted to see whether life naturally pops out in it. But now I can't find it again or any other news from that group. Does anyone know about such a simulation?
  13. Corpuscule

    Life after a PhD in physics in Australia / New Zealand?

    Hi all, I have recently finished a PhD in quantum physics. At the moment I am a postdoc in the same group. I really enjoy what I am currently doing. I am moderately successful in a sense that I will probably be able to find a second and maybe a third postdoc, but most likely not successful...
  14. S

    How Do You Calculate the Half-Life of Thorium-232?

    Homework Statement Basically, the problem asked for the half life of Thorium-232, given the initial mass and the rate of decay. \begin{equation} \frac{dN}{dt} = 4100 \frac{ \alpha }{s} \end{equation} initial mass = 1.0 gHomework Equations \begin{equation} \frac{dN}{dt} = \lambda N...
  15. T

    Life before and after "snowball Earth"

    The question is simple, was life able to recover from the very long and cold "snowball earth" epoque, which means that Earth was not completely sterile during that period, or, when climate became warmer, life simply reborn again - from scratch?
  16. I

    Any ideas what makes life, alive?

    I know this forum doesn't allow speculation but is there any good theories in science that explain how chemistry can become biology? At the start of the big bang, there was no such thing as life and now here I am, material created by the big bang that has come together in such a way that allows...
  17. L

    I want to spread life to space. What should I do?

    Our Earth is going to be engulfed by the sun eventually. Urged by a primitive desire to continue life (human or not), I decided to devote my life to the said goal. I realized this is a risky, life-long endeavour with huge chance of achieving little at best. What is the best strategy for me...
  18. M

    Extending the shelf life of Acetic Acid battery

    Why do Acetic Acid Battery power devices only for short periods of time? Does it have to do with Capacitance?
  19. B

    How to improve test taking / Figuring out life? Get out of Limbo

    Background: Physics Major (3.5 physics gpa), college graduate, pursuing PhD, PGRE: 700 52% I have seen a couple of threads on test taking, but I have a slight different direction. I don't have problems with tests in general. I have done well on many many exams ( physics, math, chemistry...
  20. I

    I need some advice. My life is a confused mess.

    Hello, everyone. To give you some context, let me give you some background about myself. I apologize if this is overly sentimental but I can't help it. As a child, I was fairly bright and very intellectually curious. I got good grades. I was always among the top two in my class. I loved...
  21. Mark Edawrds

    Experimental Physics: My Life, Career, Education?

    Hello Everyone. I'm pretty much a newb on the forum so please go easy :). My name is Mark, I'm from England, I'm in the late stages of my 15th age and I'm Home Educated. Now.. Where to start? I guess Primary School would be sufficient. Well, I started it as every other child does, however over...
  22. S

    How Long Should Radiation Therapy Last After Two Years to Match Initial Dosage?

    Homework Statement a patient who is undergoing cancer theraphy is given 10 mins of irradiation from a radioactive source that has half life = 2 years. If the same source is to be used for same treatment 2 years later , how long should the patient should be irradiated? the ans is 20 mins .. can...
  23. T

    Is CNO cycle more life friendly than H->He?

    Wiki claims in stars, heavier than 1.3 solar masses (where CNO plays major role) there is an inner convection zone near the core, but no outer convection zone. Hence, such stars should be "calmer" - no solar flares, less radiation... Am I right?
  24. M

    Is Extraterrestrial Life Possible?

    just wanted to ask your opinion about this topic to see what people think.
  25. F

    What can I make that will {improve/help/ease, etc.} your daily life

    So have you ever felt a moment where you felt like, I wished there was something like that invented/prototyped. Or have an idea that you wished to be enacted or built. Simple or Crazy, post them. I would extremely appreciate it. (I actually need it for design engineering). I got a few ideas, but...
  26. David Carroll

    Did life spring from "fossil fuels" rather than vice versa?

    I was recently doing some thinking about the relation between fossil fuels and organisms. First of all, how do scientists know for sure that fossil fuels are derived from prehistoric life? Do they assume this because fossil fuels are made of organic compounds and therefore must have come from...
  27. C

    Oldest part of the galaxy that could have held life?

    What is the oldest part of our galaxy that theoretically could have held life some millions - billions of years before earth? I'm asking purely out science fictionic curiosity. This may sound like an even dumber question, but is there any region on the "map" of the galaxy that contains these...
  28. J

    Carbon based Life vs. Plasma based Life.

    Life based on carbon needs very especial conditions to thrive, life on Earth is a clear example of that. Lots of time and research have been dedicated trying to find carbon based life elsewhere on the Universe, but that search may be too narrow because that search assumes that life can only be...
  29. vlemon265

    What an amatuer physics enthusiast do in daily life?

    My friend in mathematics department told me that one Hungarian mathematician Paul Halmos had said 'The only way to learn mathematics is to do mathematics'. Are amatuer physics enthusiast also do physics in their daily life. I want to learn from them. But what 's meant by "doing Physics"? Can...
  30. DREAMWALKER

    Want to do something meaningful in life

    Dark Side: I am a 28 year old advertising professional. I am extremely upset with the course my profession has taken. I feel unwanted in my office. I hate what I am doing for a living. On the other hand, I am extremely bad with numbers and math in particular. Bright Side: I love...
  31. Sneakatone

    Half life and decay differential EQ problem

    Homework Statement The Shroud of Turin, which shows the negative image of the body of a man who appears to have been crucified, is believed by many to be the burial shroud of Jesus of Nazareth. See the figure below. In 1988 the Vatican granted permission to have the shroud carbon-dated. Three...
  32. marcus

    Gamma ray bursts (GRB) and distribution of life

    Gammaray bursts (GRB) may affect the prevalence of life in various different regions of the galaxy. http://arxiv.org/abs/1409.2506 On the role of GRBs on life extinction in the Universe Tsvi Piran, Raul Jimenez (Submitted on 8 Sep 2014) As a copious source of gamma-rays, a nearby Galactic...
  33. F

    Finding intelligent life like us elsewhere as a main goal

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  34. Demystifier

    How does life defy the laws of thermodynamics?

    How can life be compatible with the second law of thermodynamics? Here is how. Life is a self-organized system. A self-organized system is a system in which organization arises SPONTANEOUSLY, which means that the probability of the appearance of organization is large. But this means that...
  35. Demystifier

    Quantum weirdness in everyday life

    Here is a simple analogy that helps to understand the basic idea of the Bohmian interpretation of quantum mechanics. Assume that you have recipes for two different meals. These recipes are written on papers. Hence, these recipes are real. However, when you make the meal, you use only one of...
  36. G

    Finding the New Azimuth Bearing for Triangulation in Geomagnetic Bearings

    Draw this description out on a piece of paper if you would like. I cannot figure this out, it has been years since I have done math at this level. I am standing at point A and have a distance of 87.8333 feet to Point B, my azimuth bearing is 123 degrees. I want to move over 20 feet and...
  37. K

    Battery Charging: Impact on Battery Life

    Please if we charge battery with high voltage like the battery charge voltage 4.2v and we supply 5v, is that will reduce the battery life. Thank you
  38. K

    Day in the life of an astrophycisist?

    Hi. I'm at a very critical point in my life / education. In 3 months I have to apply to the university I will attend next summer. I'm torn between studying physics or biology - I have had biology for 6 months, physics only for 1 week in my whole life. But I've been interested in astronomy since...
  39. StevieTNZ

    Extra-Terrestrial Life Discovered in Outer Space

    At least according to this article, https://nz.news.yahoo.com/a/-/world/24765825/extra-terrestrial-life-discovered-in-outer-space/ An interesting find, to say the least!
  40. A

    How Do You Calculate Mean Life and Half-Life of Radioactive Nuclei?

    Homework Statement Radioactive nuclei are produced in an irradiated sample at the rate of 10 s-1. If the number in the sample builds up to a maximum of 1000, calculate the mean life and the half-life of the radioactive nuclei Can anyone advise on this one not sure how mean life is found...
  41. K

    Career for human life span study

    This might sound crazy, but I want to study pronging human life span. I am thinking of majoring molecular nanotechnology so that I can use this major to construct an artificial enzyme(medical nanorobot) that lengthens telomere (I know this is not the only issue of aging and death). I am not...
  42. J

    MHB Optimizing Fund Allocation for Organization Expenses: A Real-World Math Problem

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  43. Ryan_m_b

    Real life examples of spring energy storage

    Tonight I've had a deceptively simple question that I've found maddeningly difficult to get an answer to. What I'm looking for is a list of springs with information on how much they can be compressed and how much energy they store. E.g.: Steel spring from company A has dimensions X, Y, Z and...
  44. gfd43tg

    Fate of outer planets after sun ends its life cycle

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  45. fras

    What Are the Realities of Job Prospects for Physics PhD Graduates?

    I will be graduating in the Fall with a degree in physics, but I am afraid. Before now, I had a plan to go to graduate school. However, I've been reading around these forums that people with PhD's in physics are broke, cannot find jobs, and the field of physics seemingly oversaturated so much so...
  46. micromass

    What do you need most in your life?

    Please select in the poll what you could use most in your life. If you want, you can tell us why :-p
  47. nsaspook

    Is Life in the Wreck Patrol As Bad As It Sounds?

    http://www.cnn.com/interactive/2014/07/world/south-china-sea-dispute/index.html
  48. A

    MHB Half Life and Exponential Growth Question

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  49. P

    Schools Mathematics (also Physics) and university life

    Hello. I would like to have some suggestion about how to make university life "more productive". I will make this clearer: 1. in the university I will attend (and pretty much in every university in my country) there are only 30-40 students of maths and 40-50 of physics; 2. it has been verified...
  50. A

    How to Calculate Population Size at T+1 Using Life Tables?

    Homework Statement http://imgur.com/OInF6O2 The blue table shows the mortality and offspring production rates per year per age class by individuals of an unnamed species. The orange tables shows the starting population at time t, I have to find the number of individuals at T+1 (next year)...
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