Monday 14 July 2014

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Quotes On Life Biography

Source Google.com.pk

Life is a characteristic distinguishing physical entities having signaling and self-sustaining processes from those that do not,[1][2] either because such functions have ceased (death), or because they lack such functions and are classified as inanimate.[3][4] Biology is science concerned with the study of life.

Any contiguous living system is called an organism. Organisms undergo metabolism, maintain homeostasis, can grow, respond to stimuli, reproduce and, through evolution, adapt to their environment in successive generations. More complex organisms can communicate through alternative means.[1][5] A diverse array of living organisms can be found in the biosphere of Earth, and the properties common to these organisms—plants, animals, fungi, protists, archaea, and bacteria—are a carbon- and water-based cellular form with complex organization and heritable genetic information.

The Earth was formed about 4.54 billion years ago. The earliest life on Earth existed at least 3.5 billion years ago,[6][7][8] during the Eoarchean Era when sufficient crust had solidified following the molten Hadean Eon. The earliest physical evidence for life on Earth is biogenic graphite in 3.7 billion-year-old metasedimentary rocks discovered in Western Greenland[9] and microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia.[10][11] Nevertheless, several studies suggest that life on Earth may have started even earlier,[12] as early as 4.25 billion years ago according to one study,[13] and even earlier yet, 4.4 billion years ago, according to another study.[14] The mechanism by which life began on Earth is unknown, although many hypotheses have been formulated. Since emerging, life has evolved into a variety of forms, which biologists have classified into a hierarchy of taxa. Life can survive and thrive in a wide range of conditions.

Though life is confirmed only on the Earth, many think that extraterrestrial life is not only plausible, but probable or inevitable.[15][16] Other planets and moons in the Solar System have been examined for evidence of having once supported simple life, and projects such as SETI have attempted to detect radio transmissions from possible alien civilizations. According to the panspermia hypothesis, microscopic life exists throughout the Universe, and is distributed by meteoroids, asteroids and planetoids.[17]

The meaning of life—its significance, origin, purpose, and ultimate fate—is a central concept and question in philosophy and religion. Both philosophy and religion have offered interpretations as to how life relates to existence and consciousness, and on related issues such as life stance, purpose, conception of a god or gods, a soul or an afterlife. Different cultures throughout history have had widely varying approaches to these issues.
Evidence suggests that life on Earth has existed for at least 3.5 billion years,[6][7][8][77] with the oldest physical traces of life dating back 3.7 billion years.[9][10][11] In a National Institutes of Health study, the authors hypothesize that if biological complexity increased exponentially during evolution, life in the universe may have begun nearly 10 billion years ago[78][79] - billions of years before the Earth existed, suggesting that Earth was seeded by panspermia or directed panspermia. All known life forms share fundamental molecular mechanisms, reflecting their common descent; based on these observations, hypotheses on the origin of life attempt to find a mechanism explaining the formation of a universal common ancestor, from simple organic molecules via pre-cellular life to protocells and metabolism. Models have been divided into "genes-first" and "metabolism-first" categories, but a recent trend is the emergence of hybrid models that combine both categories.[80]

There is no current scientific consensus as to how life originated. However, most accepted scientific models build on the following observations:

The Miller–Urey experiment, and the work of Sidney Fox, show that conditions on the primitive Earth favored chemical reactions that synthesize amino acids and other organic compounds from inorganic precursors.[81]
Phospholipids spontaneously form lipid bilayers, the basic structure of a cell membrane.
Living organisms synthesize proteins, which are polymers of amino acids using instructions encoded by deoxyribonucleic acid (DNA). Protein synthesis entails intermediary ribonucleic acid (RNA) polymers. One possibility for how life began is that genes originated first, followed by proteins;[82] the alternative being that proteins came first and then genes.[83]

However, since genes and proteins are both required to produce the other, the problem of considering which came first is like that of the chicken or the egg. Most scientists have adopted the hypothesis that because of this, it is unlikely that genes and proteins arose independently.[84]

Therefore, a possibility, first suggested by Francis Crick,[85] is that the first life was based on RNA,[84] which has the DNA-like properties of information storage and the catalytic properties of some proteins. This is called the RNA world hypothesis, and it is supported by the observation that many of the most critical components of cells (those that evolve the slowest) are composed mostly or entirely of RNA. Also, many critical cofactors (ATP, Acetyl-CoA, NADH, etc.) are either nucleotides or substances clearly related to them. The catalytic properties of RNA had not yet been demonstrated when the hypothesis was first proposed,[86] but they were confirmed by Thomas Cech in 1986.[87]

One issue with the RNA world hypothesis is that synthesis of RNA from simple inorganic precursors is more difficult than for other organic molecules. One reason for this is that RNA precursors are very stable and react with each other very slowly under ambient conditions, and it has also been proposed that living organisms consisted of other molecules before RNA.[88] However, the successful synthesis of certain RNA molecules under the conditions that existed prior to life on Earth has been achieved by adding alternative precursors in a specified order with the precursor phosphate present throughout the reaction.[89] This study makes the RNA world hypothesis more plausible.[90]

Geological findings in 2013 showed that reactive phosphorus species (like phosphite) were in abundance in the ocean before 3.5 Ga, and that Schreibersite easily reacts with aqueous glycerol to generate phosphite and glycerol 3-phosphate.[91] It is hypothesized that Schreibersite-containing meteorites from the Late Heavy Bombardment could have provided early reduced phosphorus, which could react with prebiotic organic molecules to form phosphorylated biomolecules, like RNA.

In 2009, experiments demonstrated Darwinian evolution of a two-component system of RNA enzymes (ribozymes) in vitro.[92] The work was performed in the laboratory of Gerald Joyce, who stated, "This is the first example, outside of biology, of evolutionary adaptation in a molecular genetic system."[93]

Prebiotic compounds may have extraterrestrial origin. NASA findings in 2011, based on studies with meteorites found on Earth, suggest DNA and RNA components (adenine, guanine and related organic molecules) may be formed in outer space.


Quotes On Life Sad Quotes About Love That Make Your Cry and Pain Tumblr For Girls that make you cry for girls for Him for Boys That Hurts Tagalog and Pain Tumblr 
Quotes On Life Sad Quotes About Love That Make Your Cry and Pain Tumblr For Girls that make you cry for girls for Him for Boys That Hurts Tagalog and Pain Tumblr 
Quotes On Life Sad Quotes About Love That Make Your Cry and Pain Tumblr For Girls that make you cry for girls for Him for Boys That Hurts Tagalog and Pain Tumblr 
Quotes On Life Sad Quotes About Love That Make Your Cry and Pain Tumblr For Girls that make you cry for girls for Him for Boys That Hurts Tagalog and Pain Tumblr 
Quotes On Life Sad Quotes About Love That Make Your Cry and Pain Tumblr For Girls that make you cry for girls for Him for Boys That Hurts Tagalog and Pain Tumblr 
Quotes On Life Sad Quotes About Love That Make Your Cry and Pain Tumblr For Girls that make you cry for girls for Him for Boys That Hurts Tagalog and Pain Tumblr 
Quotes On Life Sad Quotes About Love That Make Your Cry and Pain Tumblr For Girls that make you cry for girls for Him for Boys That Hurts Tagalog and Pain Tumblr 
Quotes On Life Sad Quotes About Love That Make Your Cry and Pain Tumblr For Girls that make you cry for girls for Him for Boys That Hurts Tagalog and Pain Tumblr 
Quotes On Life Sad Quotes About Love That Make Your Cry and Pain Tumblr For Girls that make you cry for girls for Him for Boys That Hurts Tagalog and Pain Tumblr 
Quotes On Life Sad Quotes About Love That Make Your Cry and Pain Tumblr For Girls that make you cry for girls for Him for Boys That Hurts Tagalog and Pain Tumblr 
Quotes On LifeSad Quotes About Love That Make Your Cry and Pain Tumblr For Girls that make you cry for girls for Him for Boys That Hurts Tagalog and Pain Tumblr 

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