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.
Hi, I had made an inquiry about regression last week and am still working on understanding the whole concept.This week my question is different. How would I use the a and b values of the regression to indicate how something is growing. Like I'm having problems interpreting data because I do not...
This promises to be a difficult contest to vote on since there are so many wonderful pictures. Still, please pick the picture that best represents our theme, which is on trees.
Note that the participants were asked to submit a photo that has the tree/s as THE main subject, and not the scenery...
The Tree Of Life
This one should be easy. Pictures this week must be on trees. Trees (or a tree) must be the main subject of your picture, not the background scenery, the people in front of it, or anything else. Please note that fake trees do not qualify.
Zz.
Contest Rules:
1. Any...
http://www.spr.ac.uk/JSPRabstracts.php3?year=2000#oct
This case concerns a young boy in Sri Lanka who made several statements regarding a previous life, among them where he had lived and how he was killed when traveling in a truck through a forest. The boy associated two birthmarks with his...
I bought a fairly cheap wireless mouse a while back. With the batteries it came with it lasted quite some time, at least a few months, before it died. I bought new batteries from the store that were on sale and put one in. About a week later I found that the usb plug had come detached from...
Hi All,
We have manufactured a custom bolt (similar to standard bolt).
Now we need to calculate the fatigue life of the bolt.
Could you please guide me in calculating the fatigue life?
Thanks,
Ana
Rather bored, so I was just wondering - only considered generalizations with the underling principle here, but I'm looking for specifics: have your interests in physics/mathematics altered your love life in any way?
Say, have you pissed your significant other off with your obsession with...
Do any of you get this channel? Have you seen the show "Get Out"? It's a travel show where these three girls travel around the world and tell you about it. Oh, and they only wear bikini tops and they only go to tropical areas. I can't get enough of this show. It is so sexist, because these girls...
Hi,
I was having a discussion with a friend about the probability of life in the universe outside of earth.
From what i know, there are 70 000 000 000 000 000 000 000 stars and god knows how many planets. Given the low probability of life spawning on a single planet but the huge amounts of...
I am on a computer at a public library, and I only have fifteen minutes left. So this post definitely won't be as well-polished as most of my posts.
I am interested in living a simple life out in the country. I want to buy some land out in the country and build a cabin on it. I could heat...
I wrote something which I believe gets to the origin of fashion and gossip in a simple and logical way. I would be happy with any comment on whether it makes sense to you or not.
Why do women find it important to be in on the latest fashion trends and gossip? Fashion's use couldn't be just...
Researchers think they have found traces of ammonia in Mars' athmosphere.
Since ammonia is degraded quickly there, if this were true, it would mean the presence of some ammonia-producing source on Mars.
THe best bets for that would be either active volcanoes or microbes, but since active...
Interesting publication:
http://www.chemie.de/news/e/84187/
In normal geology jargon, this means that they are pretty convinced to be on to something. However:
What they found was depletion of heavy 13C atoms reducing the d13C ratio to values comparable to photosynthesis nowadays as...
We learned that life prefers to use glucose over other sugars (catabolite repression).
1) Why is glucose preferred?
2) Why do sperm use fructose instead of glucose?
Ok,
I have been to these forums a lot in the past year or so and I have learned a lot and asked a lot. But recently my past year has just been a drag - it is my first year in university and I know that some or maybe even majority will say it is only first year. But I don't think it is that, I...
I've just finished my first year in engineering (Electronics and Electrical), and when I started out, I eventually wanted to do a Phd in mathematics because I soon realized that I loved mathematics and that I can grasp the intricacies without busting my head. I had dreamed of focusing on...
What are the little things that make you happy?
I just realized one for me that seems funny to a former city kid: The day our pasture gets mowed is one of the better days of the year. The grass grows to four and five feet tall here, and as the spring progresses, the field sort of closes-in...
Where did "life" come from?
There is something about this "big bang" theory that makes me not to accept it at all and that's: Life. Physicists have all tried to put together their observations and I mean observations only to come up with this big bag theory, but at the same time there exist...
When I was in college, I had some direction, even if it was just the pursuit of a diploma. Now that I'm done, I feel like I'm stranded in mid-ocean with no discernible wind or current pushing me in any direction. Admittedly, this is my fault. I had a narrow focus and was concerned only with...
After the initial shock and excitement, do we commandeer the the planet and take if for ourselves anyway? Pollute it with Earth species or extremophiles?
Will an environmental impact study then be required?
And if they are more advanced, do we hide and hope they didn't see us lest they do...
The soil on Mars has been found to have nutrients which would be conducive to supporting life:
http://www.msnbc.msn.com/id/25396378/
All the more reason for us to go and start farming over there.
of late i have discovered the beautiful smell that my lemon myrtle can give when i rub the leaves together between my hands. It got me thinking, what can i do to get this smell throughout my house?
i have thought of two ideas so far (iam open to any others): dry the leaves and turn it into an...
What does the presence of life on Earth imply about the chance of life existing on other worlds?
Can one assume, with high probability, that despite Earth's seeming singularity of life, there is life elsewhere in our (assumed finite) universe? In our (assumed infinite) universe?
A...
http://www.quixtar.com/
I saw that Amway now has a slick advertising campaign running on TV. I don't have the time to comment on this in detail right now, but I can say that I got involved in Amway when I was 18 years old. I had a downline of over 50 people, including one of the richest men...
I find myself very interested in Cosmology and would consider doing a PhD in the field, however I am not sure if I would like to be an academic or not.
Given the relatively few technical applications of Cosmology, would it be wiser for me to enter a field with greater possibilities for...
How can we justify that one life is more important than Another's?
I've been wondering about this for a while now. I've tried tackling this from a religious and scientific standpoint.
For religion I've looked at the Indian Caste system and at the Christianity belief that we should put...
im confused with almost everything i want in my life right now, and I am already a junior in college, becoming a senior next year. i don't know whether i want to pursue math, physics, or engineering
i don't know how i should focus my time to improve academically and/or socially. if i choose to...
There have been several books, documentaries, webumentaries, and even a Hollywood movie in "I Am Legend" relating and discussing this topic which encourages people to imagine world without people.
A new documentary by The History Channel premiered after the success of "I Am Legend" called...
Nearly every machine in the factory decides to self destruct on my watch, i loose my Internet
connection for no apparent reason, there is a pool of water in the kitchen because my fridge decided to switch itself off, and all the stuff inside looks perished.
All in all a good day as no one...
I just finished my first year of a 4 year physics degree, and it made me realize that although I love physics and I am really good at it, but I do not want to be a physicist. This has a lot to do with my first taste of research life with a condensed matter group I had been helping. It made me...
questions about life of gamma ray particle
question-are gamma ray particles unchanged after gamma ray burst 13 billion years ago?
question-are changes detected not due to travel through normal space, scattering? changes due to dark matter/energy?
question-positronium decay at end universe...
I was doing some reading on the effects of air blasts from asteroid impacts when I realized that I've never seen any data of the potential effect on marine life. Since sound travels farther and faster in a liquid, wouldn't an asteroid impact in a large ocean (liquid) have a more profound...
I work at a LAN center, and we recently got an In The Groove arcade machine. (http://www.freewebs.com/bhsddr/In%20The%20Groove%202%20dedicated%20cabinet.jpg" )
It's great, but the only problem is that there is a basement underneath us, and the building is fairly old. When people play on it...
http://www.practicalfishkeeping.co.uk/pfk/pages/item.php?news=1669
Now that the turtle is living in a safe environment, he is really coming out of his shell.
GaP life question!??
Hi, i have a question. I hope someone could help me... Thenks in advance!
1.- I've read that the GaP life is sensitive to the temperature. Can you explain this in more detail?! I mean, what happens at low and high temperature and why.
2.- I've been calculating DOS...
I especially like this part:
& lastly, universal health care would probably reverse the trend:
http://www.iht.com/articles/2008/03/23/america/health.php
Could there be a civilised way to live without central government? suppose some catastrophe wiped out your countries government, would there be a priority to replace
it?
I've actually been reading a number of things. First, I read Lars Eigner's "On Dumpster Diving" and afterward, a few existentialist documents paired with some Budhist doctrine. All of philosophy aims to give meaning to human life...and apparently society, at the same time, implements meaning...
In your opinion, what are my options in life based on my pedigree alone
Just turned 24, graduated 1.5 years ago with a degree in physics/astronomy. I'm in between jobs. I have a 2nd interview with a financial software company that deals with hedge funds/private equity, banks, etc.
I have a...
Hi everyone.
I'm just wondering - I've heard lots of rumors about physics grad. school, and how hard it is, etc. I have no problem dedicating myself to studying, but am worried about family issues. What I'm wondering is -
- how many hours on average per week will I be working? 40, 60, 80...
Predictability:
Everything in this world has a certain amount of predictability; some call it “odds”.
I’m still young at 33, but I find it boring and redundant to even bother doing a lot of things in my life now. In some cases, it irritates me when someone asks me for my advice, or if someone...
I'm thinking about studying for mechanical engineering, but I'm slightly discouraged by the amount of work people say they have to put forth. but is there really that little amount of free time to hang out with friends and do things you enjoy? i mean, will i still have to for my gf and what not...