The Universe:

Most astronomers today believe that the universe began with a cosmic explosion, the Big Bang, that occurred throughout all space at the beginning of time, approximately 15 billion years ago.

In the very beginning, all matter in the universe was concentrated in a state of infinite density. At the Big Bang, when the temperature of the universe reached an incredible 10 billion degreee Kelvin, the universe began to expand, marking the creation of the universe. In the next 3 minutes, when the temperature began to drop to less than 1 billion degree Kelvin, the nucleosynthesis began, filling the universe completely with high-energy photons colliding vigorously with protons and electrons. At this time, the universe was in its "primordial fireball" state that it was opaque. 1 million years after the Big Bang, when the energy of the photons became too weak to keep the protons and electrons apart, the protons and the electrons started to combine to form hydrogen atoms as temperature dropped below 3000 K. At this time, atoms became the most stable form, and since they are much smaller than visible light that they do not block the photons, the universe became transparent as we know it today.

The Earth:

"It is dawn, 4,600 million years ago. Earth is in the violent red throes of its beginnings..." -- Margulis & Sagan


In its earliest stage, approximately 4.6 billion years ago, Earth was a fire ball-- a gravitational implosion of molten rocks and swirling metal. Its surface and atmosphere were occupied by gases such as ammonia, hydrogen sulfide, and methane in their superheated states, zapping everywhere and at everymoment by lightning. Meanwhile, the sun has ignited, sending bursts of powerful radiation onto Earth.

Meteors of different sizes, ranging from dust specks to small planetoids, at the same time, continue their bombardments. While these bombardments brought water and carbon compounds along onto Earth, they also brought in incredible amounts of (kinetic) energy, which along with the decay of radioactive isotopes, melted the solid material collected on Earth from the earlier planetesimals(Margulis & Sagan). Gravity then caused abundant, dense iron to sink toward the Earth's center, forcing less dense material to the surface. This process of chemical differentiation then produced a layered structure within the Earth: a central core composed of almost pure iron, surrounded by a mantle of dense, iron-rich minerals. This mantle, in turn, is surrouned by a thin crust of relatively light silicon-rich minerals (Kaufmann).

The Creation of life: People once believed that bacteria could spring spontaneously from non-living things, which was later proven "wrong" by Pasteur with his famous twitched-neck flask experiment. Ironically, today, we've realized that the very first life on Earth was indeed originated from abiotic surroundings. In fact, organic molecules have been successfully generated from abiotic elements by scientists Miller and Urey.

The abiotic chemical evolution of life follows 4 major steps:

1. the abiotic synthesis and accumulation of small organic molecules, or monomers, such as amino acids and nucleotides; 2. the joining of these monomers into polymers, including proteins and nucleic acids; 3. the aggregation of abiotically produced molecules into droplets, protobionts, that had chemical characteristics different from their surroundings; and 4. the origin of heredity. (Campbell)

To understand how this creation of life from abiotic material occured, we have to consider 2 critical ideas (F. Shu): 1. The extension of the idea of natural selection to chemical level. 2. The realization that the condition of the early Earth when life first arose must have been vastly different from present: a) non-oxidizing atmosphere: present level of oxygen, which began to accumulate around 2.1 billion years ago with the presence of cyanobacteria, would have been lethal to primitive organisms b) abundant resources produced non-biologically c) long time scale without competition

Stanley Miller and Harold Urey used an apparatus similar to this one to simulate chemical dynamics on the primitive Earth. A warmed flask of water simulated the primeval sea. The "atmosphere" consisted of H2O, H2, CH4, and NH3. Sparks were discharged in the synthetic atmosphere to mimic lightning. A condenser cooled the atmosphere, raining water and any dissolved compounds back to the miniature sea. As material circulated through the apparatus, the solution in the flask changed from clear to murky brown. After one week, Miller and Urey analyed the contents of the solution and found a variety of organic compounds, including some of the amino acids that make up the proteins of organisms. (Campbell)

As mentioned earlier under the section "The Chemical Aspects of the Origin of Life", life did indeed originated from its abiotic surroundings. Thus, it is important for us to learn about the physical and chemical environments of the primitive Earth.

The atmophere of primitive Earth consisted of reactive, naturally availabe, molecules:

Nitrogen (N2), water (H2O), methane (CH4), and ammonia (NH3), etc. These molecules are basically what was needed to creat life -- in fact, the percentage of hydrogen, oxygen, nitrogen, and carbon, together consists 99.5 % of all matters. Along with carbon's versatility, constructions of an inexhaustible variety of organic molecules using roughly the same proportions of the essential elements thus took place. In fact, the percentage of essential elements of life -- C, N, O, H, P, and S -- are quite similar from individuals to individuals.

Energy wise, the primitive Earth had plenty from a variey of sources:

1. Radiation: from the cosmic and radioactive isotope decays 2. UV light: there were no protective ozone layer then 3. Electrical discharge: from the never ending lightning 4. Heat: young crust was volcanically acitve

Following are a few molecular clues to the origin of life on Earth presented by Prof. Shu of UC Berkeley:

Molecules of living organisms are rich in hydrogen-containing carbon compounds. This suggests that there were little or no free molecular oxygen on primitive Earth.

All amino acids exist in both the right-handed state and the left-handed state. However, only 20 amino acids of the left-handed variety are used by living organisms in proteins. Therefore, suggesting that there was one single origin of life.

DNA and RNA are the universal basis of all life forms on Earth.

ATP is the universal energy currency of all living organisms; suggesting a common origin of metabolism.

In any cell, first steps of carbohydrate metabolism involve fermentation, with the last steps in aerobic organisms the usage of oxygen via respiration -- suggesting that aerobic organisms evolved from anaerobic ones.


Prokaryotes (commonly known as bacteria), the simplist forms of life, originated a few hundred million years after Earth's crust cooled and solidified. The oldest evidence of life found as of today are fossils resembling spherical and filamentous prokaryotes found in stromatolites that are 3.5 billion years old in southern Africa and Australia. These fossils appear to be photosynthetic, however, suggesting that the earliest life probably had evolved prior to that of 3.5 billion years ago. (see the dating methods)

One of the essential episodes in the formation of life on Earth involved the formation of a selectively permeable membrane that could enclose a solution of different composition from the surrounding solution, therefore providing a stable environment, while still allowing exchanges of nutrients and wastes. This may sound like a very complicated process, however, under the goverance of the laws of chemistry, it really was not too difficult -- all it takes was some of the abiotic elements that were spontaneously available on the early Earth.

The formation of the biological membrane and its selective permeability to various substances is the one most important factor that led to the origination of life. However, this formation, despite its importance, is quite simple. In fact, it's simultaneous -- provided that all the essential elements are available (which were -- please refer to the section The Conditon of the Early Earth).

When phospholipids are mixed with water, they self-assemble to form films due to insolubility. Agitation then breaks the films into sphere. Even these primitive membranes have some ability to control the passage of substances between the contents of a sphere and the aqueous environment outside. Phospholipids were probably among the organic molecules that predated life on the primitive Earth, and their spontaneous assembly to form membranes was a major step toward protocells that could maintain internal environments differing from the surroundings (Campbell).

\After the formation of the biological membrane, the protocell then follow the 4 major steps of chemical evolution (click here to review the 4 steps..), which then led to the formation of the most primitive life -- the prokaryote, commonly known as the "bacteria". The prokayrotes are the single-celled organisms that have successfully acquired the biological membrane system, but lack the endomembrane systems found in the more advanced eukaryotes.

The prokaryotes thus were the earliest organisms, and they lived and evolved all alone on Earth for 2 billion years. They had continued to adapt and flourish on a changing Earth, and in turn they have helped to change the Earth (Campbell).

The eukaryotes, on the other hand, are more advanced with endomembrane systems. That is, they evolved the ability to "engulf" other prokaryotes and acquire whatever function the prokaryotes were capable of. For example, endocytosis of cyanobacteria (a prokaryote) gives some eukaryotes the ability to perform photosynthesis. Other examples include the engulfing of golgi apparatus, mitochondria, etc. With this incredible ability, the eukaryotes were able to evolve into more advanced organisms such as human beings.


 Science & Mathematics

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