Evolution-1 Flashcards
what is the big bang? when was our solar system formed
. The Big Bang theory attempts
to explain to us the origin of universe. It talks of a singular huge explosion
unimaginable in physical terms. The universe expanded and hence, the
temperature came down. Hydrogen and Helium formed sometime later.
The gases condensed under gravitation and formed the galaxies of the
present day universe. In the solar system of the milky way galaxy, earth
was supposed to have been formed about 4.5 billion years back.
describe the interaction of various gases as the earth cooled down
There
was no atmosphere on early earth. Water vapour, methane, carbondioxide
and ammonia released from molten mass covered the surface. The UV rays
from the sun brokeup water into Hydrogen and Oxygen and the lighter H2
escaped. Oxygen combined with ammonia and methane to form water,
CO2
and others. The ozone layer was formed. As it cooled, the water vapor
fell as rain, to fill all the depressions and form oceans. Life appeared 500
million years after the formation of earth, i.e., almost four billion years back.
Did life come from outerspace? what was the notion of early greek thinkers
Some scientists believe that it came
from outside. Early Greek thinkers thought units of life called spores
were transferred to different planets including earth. ‘Panspermia’ is still
a favourite idea for some astronomers.
theory of spontaneous generation
For a long time it was also believed
that life came out of decaying and rotting matter like straw, mud, etc.
This was the theory of spontaneous generation.
how was the theory of spontaneous generation dismissed
Louis Pasteur by careful
experimentation demonstrated that life comes only from pre-existing life.
He showed that in pre-sterilised flasks, life did not come from killed yeast
while in another flask open to air, new living organisms arose from ‘killed
yeast’. Spontaneous generation theory was dismissed once and for all.
what was haldane and oparin’s proposition
Oparin of Russia and Haldane of England proposed that the first form
of life could have come from pre-existing non-living organic molecules
(e.g. RNA, protein, etc.) and that formation of life was preceded by chemical
evolution, i.e., formation of diverse organic molecules from inorganic
constituents. T
describe s miller’s expt
The conditions on earth were – high temperature, volcanic
storms, reducing atmosphere containing CH4
, NH3
, etc. In 1953, S.L. Miller,
an American scientist created similar conditions in a laboratory scale
(Figure 6.1). He created electric discharge in a closed flask containing
CH4
, H2
, NH3
and water vapour at 800oC. He observed formation of amino
acids. In similar experiments others observed, formation of sugars,
nitrogen bases, pigment and fats. Analysis of meteorite content also
revealed similar compounds indicating that similar processes are
occurring elsewhere in space. With this limited evidence, the first part of
the conjectured story, i.e., chemical evolution was more or less accepted.
when did first non cellular form of life originate
The first non-cellular forms of life could have originated
3 billion years back. They would have been giant molecules (RNA, Protein,Polysaccharides, etc.). These capsules reproduced their molecules perhaps.
The first cellular form of life did not possibly originate till about 2000
million years ago. These were probably single-cells. All life forms were in
water environment only. This version of a biogenesis, i.e., the first form of
life arose slowly through evolutionary forces from non-living molecules is
accepted by majority. However, once formed, how the first cellular forms
of life could have evolved into the complex biodiversity
what is the theory of special creation ( 1st thery of evolution(
Conventional religious literature tells us about the theory of special
creation. This theory has three connotations. One, that all living organisms
(species or types) that we see today were created as such. Two, that the
diversity was always the same since creation and will be the same in future
also. Three, that earth is about 4000 years old.
what was charles darwin
s opinion of existence of various life forms
Based on observations
made during a sea voyage in a sail ship called H.M.S. Beagle round the
world, Charles Darwin concluded that existing living forms share
similarities to varying degrees not only among themselves but also with
life forms that existed millions of years ago. Many such life forms do not
exist any more. There had been extinctions of different life forms in the
years gone by just as new forms of life arose at different periods of history
of earth. There has been gradual evolution of life forms
describe the natural selection method of evolution
Any population has built in variation in characteristics. Those characteristics which enable
some to survive better in natural conditions (climate, food, physical factors,
etc.) would outbreed others that are less-endowed to survive under such
natural conditions. Another word used is fitness of the individual or
population. The fitness, according to Darwin, refers ultimately and only
to reproductive fitness. Hence, those who are better fit in an environment,
leave more progeny than others. These, therefore, will survive more and
hence are selected by nature. He called it natural selection and implied it
as a mechanism of evolution.
Alfred Wallace, a
naturalist who worked in Malay Archipelago had also come to similar
conclusions around the same time. In due course of time, apparently new
types of organisms are recognisable. All the existing life forms share
similarities and share common ancestors. However, these ancestors were
present at different periods in the history of earth (epochs, periods and
eras). The geological history of earth closely correlates with the biological
history of earth.
