Life on Earth POINT 1

7/31/2019 Life on Earth POINT 1

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Life on Earth


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1. Analysis of the oldest

sedimentary rocksprovides evidence for

the origin of life


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identify the relationship between the conditions on

early Earth and the origin of organic molecules

The Earth is thought to be approximately 4.5 billion years old

This was during the Hadeon eon

Gaseous cloud was transformed into a solid body

The heavier molten iron sank down to become the core

While the lighter rock rose to the surface and became the crust

The high temperatures at the core and resulting volcanic activity, caused

gas emisions of volatile substances such as water (H2O), methane (CH4),

ammonia (NH3), hydrogen (H2), nitrogen (N2), and carbon dioxide(CO2)

The atmosphere was ANOXIC (no free oxygen O2)

Oxygen was bound up in water and carbon dioxide

There was no ozone layer (O3) and this exposed the surface of the Earth to

UV radiation


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So how did the first organic molecules form?

Early Earth consisted of an atmosphere of water vapour, hydrogen,methane and ammonia all the elemental requirements for making

organic molecules

The main energy for the conversion into organic molecules came from the

sun

UV radiation (as no ozone existed), lightning hot springs, volcanic activityand meteorite impacts could have provided energy too.

Organic chemicals would have likely formed in the lower atmosphere or

Earths surface.

Dense clouds of water vapour would have formed a protective shield from

the suns penetrating heat. Meteorite impacts would have declined due to the protective l;ayer.

Temperatures would have cooled resulting in the condensing of vapour

clouds into liquid water and falling as rain


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Rain would have washed organic molecules into lakes and ponds, creating

new organic molecules.

Carbon dioxide would have dissolved in water forming carbonic acid,

which would have reacted with calcium in the oceans to form calciumcarbonate

Heat dissipated into space and the crust formed by the cooling of the

Earth.

Over the next 3.5 billion years, carbon dioxide content decreased as it was

incorporated in rocks as limestone.

The main remaining gas was nitrogen (78%)


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Discuss the implications of the existence of organic

molecules in the cosmos for the origin of life on Earth

There is little evidence for the existence of organic molecules in the

cosmos

Strong evidence would suggest that the organic molecules that we have

here on Earth had an extraterrestrial origin.

The Murchison meteorite in 1969, provided some evidence that thecosmos has some similarities in the organic molecules found on earth

today.


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Describe two scientific theories relating to the evolution of

the chemicals of life and discuss their significance in

understanding the origin of life

Panspermia

This theory involves the origin of organic molecules coming from thecosmos.

Materials found in meteorites and comets have revealed the presence oforganic molecules which may have acted as seeds falling onto early

earth.Biochemical formation on Earth

Oparin and Haldane suggested that organic compounds could haveformed in the oceans of early Earth from simple inorganic compounds.

The energy for this would have been provided by UV radiation from the

sun. A primoidal soup of organic compounds would have formed in the

oceans.

This theory had no evidence, until Urey and Miller conducted experimentsto show that it was possible to get organic compounds from inorganicones.


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Gather information from secondary sources to describe the

experiments of Urey and Miller and use available evidence

to analyse the:

reason, result, importance and contributions to theorigin of life.


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Reason for their experiments

They endeavoured to show if it was experimentally possible for organic

compounds to be formed from the inorganic compounds thought to be

found on early Earth ie they tried to back up the theory of Haldane andOparin.

The gases present on early Earth (CH4, NH3, H2, H2O) were in a sealed glass

chamber.

An electrical spark was used to create the energy, to simulate lightning

that would have been frequent on early Earth.

Result of their experiments

After a week, the experiment resulted in a solution containing aminoacids, which are vital components in living things.


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Importance of their experiments in illustrating the nature and practice ofscience

Anyone can propose a theory as to how something works, why something

is the way it is or, in this case, how organic molecules formed on Earth. BUT it is the nature and practice of science to test such theories and

hypotheses by conducting experiments

This is what Urey and Miller did. They took the theory of Haldane andOparin, and scientifically tested to see if it was possible to create organicmolecules (amino acids) from the inorganic ones found on early Earth.

They repeated their experiments and they yielded the same result, whichis a key factor in the scientific method.

Contribution to hypotheses about the origin of life

Urey and Miller showed that it was possible to experimentally gat aminoacids, and this gave some credence to the theory that organic moleculesarose on Earth (and not from the cosmos).

It does, however, NOT prove that this is the way that they formed. Itsimply says that it is possible that they did.


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Discuss the significance of the Urey and Miller

experiments of the primitive atmosphere

Urey and Millers experiments provided the first experimental evidence

that it was possible to produce living (organic) substances.

This has been called the chemosynthetic origin of life.

The experiments were replicated to produce a similar outcome.

Some scientists have replicated the experiment, but used UV light insteadof electricity, and still produced amino acids

Another scientist, Oro, produced adenine which is an organic compound

found in DNA and ATP.

Urey and Millers experiments have opened up significant debate as to the

origin of these organic molecules. Debates have centered around the factthat there is some geological evidence to suggest that there was no free

H2, and other evidence suggests there was.


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Identify changes in technology that have assisted in

the development of an increased understanding of

the origin of life and evolution of living things.

Francesco Redi used glass jars and cotton wool to test his theory of

spontaneous generation with flies and meat. This tested the idea that

organisms could originate from non-living matter.

Louis Pasteur disproved spontaneous generation by using his classic swan-

necked flask experiment. Leeuwenhoek and his light microscope allowed the viewing of organisms

not visible with the naked eye.

More recent technologies include the development of the electron

microscope. This led to the understanding of the molecular structure of

living things, the remains of microorganisms and mineral nature of earlyrocks

Radiometric dating has helped determine the geological age of fossils and

surrounding rock material


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Seismology provided knowledge of the structure of the Earth and the of

characteristics earthquakes.

Geology and geophysics used information about the fossil record,

concepts of continental drift and seas floor spreading to establish the ageof the Earth.

The discovery of the absolute age of fossils by looking at the relative

proportions of radioisotopes

X-ray crystallography has been used to determine the structure of various

compounds and molecules such as DNA structure.

Biochemical analysis, amino acid and nucleotide sequencing has allowed

comparisions between ancient material and modern compounds, as well

as comparative studies of different organisms.

Life on Earth POINT 1

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