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ORIGIN OF EARTH
The earth is presumed to have originated either planetesimal hypothesis and nebular hypothesis.
Origin of the UniverseThe universe began about 14.4 billion years ago
The Big Bang Theory states that, in the beginning, the universe was all in one place
All of its matter and energy were squished into an infinitely small point, a singularity
Then it exploded
The tremendous amount of material blown out by the explosion eventually formed the stars and galaxies
After about 10 billion years, our solar system began to form.
1.
Gradual condensation of interstellar dust from which our entire solar system is presumed to be formed.
The Nebular Hypothesis
2.
Earth is ~ 4,570,000,000 years old
The Age of the Earth
Meteorites give us access to debris left over from the formation of the solar systemWe can date meteorites using radioactive isotopes and their decay products
THEORIES OF ORIGIN OF LIFE
Several attempts have been made from time to time to explain the origin of life on earth.
As a result, there are several theories which offer their own explanation on the possible mechanism of origin of life.
Following are some of them:
1. THEORY OF SPECIAL CREATION
All the different forms of life that occur today on planet earth : created by super natural power.
This idea is found in the ancient scriptures of almost every religion.
Hindu mythology : Lord Brahma, the God of Creation,
Christian : God created this universe, plants, animals and human beings in about six natural days.
Sikh mythology : all forms of life including human beings came into being with a single word of God.
Special creation theory believes that the things have not undergone any significant change since their creation.
The theory of Special Creation was purely a religious concept, acceptable only on the basis of faith.
It has no scientific basis.
2. COSMOZOIC THEORY (THEORY OF PANSPERMIA
According to this theory, life has reached this planet Earth from other heavenly bodies(plnet or stars) such as meteorites, in the form of highly resistance spores of some organisms.
Highly resistant spores : lead to life on earth, named as “cosmozoa”.
This idea was proposed by Richter in 1865 and supported by Arrhenius (1908) and other contemporary scientists.
This theory lacks evidence, hence it was discarded.
3. THEORY OF CATASTROPHISM
modification of the theory of Special Creation.
It states that there have been several creations of life by God, each preceded by a catastrophe resulting from some kind of geological disturbance.
According to this theory, since each catastrophe completely destroyed the existing life, each new creation consisted of life form different from that of previous ones.
4. THEORY OF SPONTANEOUS GENERATION/ABIOGENESIS
Living organisms could arise suddenly and spontaneously from any kind of non-living matter.
One of the firm believers in spontaneous generation was Aristotle, the Greek philosopher.
Dead leaves falling from a tree into a pond would transform into fishes and those falling on soil would transform into worms and insects.
Some insects develop from morning dew and rotting manure.
Egyptians believed that mud of the Nile river could spontaneously give rise to many forms of life.
Thales (624-548 BC) suggested that oceanic water was the mother from which all living forms originated.
According to Empedocles life originated by itself from non living matter and imperfect forms were replaced by perfect forms.
Aristotle (384-322 BC) proposed that living forms are animated forms of non-living matter. He further stated that the vital forces operate constantly and improve the living world.
In the 17th century the idea of abiogenesis was opposed by an Italian physician Francisco Redi (1621-1697). For the first time he proposed through experiments, that life could arise only from pre-existing living things.
Experiment: sealing meat inside four closed flask, while leaving another four meat filled flasks open. Soon the meat in the open flasks was full of maggots.
Flies were entering and leaving the flask. Even after many days no worm appeared in the closed and sealed flask. This experiment confirmed his idea that new life can come only from early life.
14.2 The Origin of Life
Origins: Early Ideas
The History of Life
Spontaneous generation is the idea that life arises from nonlife.
Francesco Redi, an Italian scientist, tested the idea that flies arose spontaneously from rotting meat.
Chapter 14
3.
The theory of biogenesis states that only living organisms can produce other living organisms.
The History of Life
Louis Pasteur designed an experiment to show that biogenesis was true even for Microorganisms.
5. Theory of Biogenesis
Chapter 14
4.
Origins: Modern Ideas
Biochemical origin of life
Simple organic molecule formation
The primordial soup hypothesis was an early hypothesis about the origin of life.
Organic molecules could have been synthesized from simple reactions.
UV light from the Sun and electric discharge in lightning might have been the primary energy sources.
Modern Hypothesis of origin of Life
Chapter 14
Stanley Miller and Harold Urey were the first to show that simple organic molecules could be made from inorganic compounds.
The History of Life
Later, scientists found that hydrogen cyanide could be formed from even simpler molecules in simulated early Earth environments.
14.2 The Origin of Life
Chapter 14
5.
THE ORIGIN OF LIFE Origin of life is NOT an event Origin of life is a continuous process Stages
inorganic production of key simple organic moleculesproduction of more complex molecules that can synthesize
more of the same moleculedevelopment of a genetic code of self-replicating
molecules (RNA,DNA,proteins)production of the first cell by separation of these codes
from the outer world by a membrane Ocean environment by 4.0 by- fossils evident at
3.8by
THE ORIGIN OF LIFE Many complex organic molecules must have formed
before an organism produced
This process cannot occur on Earth today because the simple organism would be destroyed by oxidation or predation.
STEPS IN THE ORIGIN OF LIFE Aerobic vs. Anaerobic
oxygen poisons living cells so early life was anaerobic
Lack of free Oxygen >> No Ozone layer UV radiation kills cells so life had to originate at depth Water depths of 10m or more
Models non-oxidizing secondary atmosphere rich in the constituent
chemicals for life--H2O, CO2, N Energy in the form of UV radiation & Hot springs
STEPS IN ORIGIN OF LIFE Before the first cell>>Chemical Evolution
production of significant molecules necessary for life Phosphoric acid -can bond molecules and promote
long chain molecule formation Amino acids formed first since they do not form if
oxygen presentprobably formed on clay surfaces since they are attractive
and absorptive, also protection from UV Larger Molecules
amino acids are linked together by dehydration synthesis (water loss), clays have potential to absorb water, thus amino acids could be linked on clay surfaces
EXPERIMENTAL STUDIES A. I. Oparin- 1930s
Produced sugars and fatty acids from the constituents of an early atmosphere
Urey and Miller- 1953Production of cyanide, formaldehyde and 4 different
amino acids from water vapor, methane, hydrogen and ammonia and electrical sparks
Subsequent ExperimentsProduction of 18 of the 20 known amino acids and
extremely simple forms of DNA from gases rich in water vapor, CO2, and nitrogen and UV radiation
S.W. Fox (1959) produced protein-like (protenoids) chains from a mixture of 18 amino acids at 70oC in the presence of phosphoric acid
THE ENVIRONMENT FOR LIFE Volcanic Hot Springs Oceanic hydrothermal
vent system Deep (below the level of
UV penetration) Clays and/or Zeolites as
templates Similarity with present
day chemosynthetic heterotrophic organisms
THE FIRST CELLS All cells use the same genetic code Archaeobacteria- most primitive
Heterotrophs: obtain energy from surroundings by some chemical reaction
Obtain energy by converting CO2 and H2 to CH4 or by the reduction of sulfur compounds
Eubacteria10 Phyla, including cyanobacteria (Autotrophs:
manufacture their own food source) First Cells poorly developed metabolic systems
absorbed nutrients directly fermentation
LIFE Prokaryota
Appear 3.8-3.6 by no nucleus single loop chromosome with all genes reproduction-binary fission
Eukaryota Single cell appear 2 by Multicellular appear as trace fossils 1by and as body fossils
700my Nucleus with 2 pairs of chromosomes (2 copies of all genes) Asexual and SEXUAL reproduction>> more combinations
HOW DID LIFE ORIGINATE?
Living things (even ancient organisms like bacteria) are enormously complex.
Instead life almost certainly originated in a series of small steps, each building upon the complexity that evolved previously:
1. Simple organic molecules were formed.
Simple organic molecules (nucleotide)- the building blocks of life.
Experiments suggest that organic molecules could have been synthesized in the atmosphere of early Earth and rained down into the oceans.
RNA and DNA molecules — the genetic material for all life — are just long chains of simple nucleotides.
2. Replicating molecules evolved and began to undergo natural selection.All living things reproduce, copying their genetic material and passing it on to their offspring.
Thus, the ability to copy the molecules that encode genetic information is a key step in the origin of life — without it, life could not exist.
This ability probably first evolved in the form of an RNA self-replicator — an RNA molecule that could copy itself.
Many biologists hypothesize that this step led to an "RNA world" in which RNA did many jobs, storing genetic information, copying itself, and performing basic metabolic functions.
Today, these jobs are performed by many different sorts of molecules (DNA, RNA, and proteins, mostly), but in the RNA world, RNA did it all.
3. Replicating molecules became enclosed within a cell membrane.The evolution of a membrane surrounding the genetic material provided two huge advantages: the products of the genetic material could be kept close by and the internal environment of this proto-cell could be different than the external environment.
4. Some cells began to evolve modern metabolic processes and out-competed those with older forms of metabolism.
everything changed when some cell or group of cells evolved to use different types of molecules for different functions: DNA (which is more stable than RNA) became the genetic material, proteins (which are often more efficient promoters of chemical reactions than RNA) became responsible for basic metabolic reactions in the cell, and RNA was demoted to the role of messenger, carrying information from the DNA to protein-building centers in the cell.
Cells incorporating these innovations would have easily out-competed "old-fashioned" cells with RNA-based metabolisms, hailing the end of the RNA world.
5. Multicellularity evolved.
As early as two billion years ago, some cells stopped going their separate ways after replicating and evolved specialized functions.
They gave rise to Earth's first lineage of multicellular organisms, such as the 1.2 billion year old fossilized red algae.
BOOK AND WEB REFERENCES
Book Name : 12th Std NCERT
http://en.wikipedia.org/wiki/Abiogenesis http://www.livescience.com/13363-7-theories-
origin-life.html http://education-portal.com/academy/lesson/the-
origin-of-life-on-earth-theories-and-explanations.html
IMAGES REFERENCES
1.http://d2hh5u5wjpwmol.cloudfront.net/wp-content/uploads/2011/03/universe.jpg
2.http://upload.wikimedia.org/wikipedia/commons/4/48/Planet_formation.jpg
3.http://bekarice.com/wpcontent/uploads/2014/07/spontaneous-generation.jpg
4.https://encryptedtbn1.gstatic.com/images?q=tbn:ANd9GcR1b_XWavXhz_GyL64OOa3ylkawCKXVta2rctLCcA_zxHa_UhRF
5.http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Miller.gif
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