Biology Lecture No. 2: The Origins Of Life & The Primordial Soup
Wednesday January 11 , 2012
The Origins Of Life:
-The estimated age of the Earth is known to be around 4.6 billion years.
-Although the first evidence of life (prokaryotic cells) is known to have existed 3.8 billion years ago, life
may have actually originated around 4 billion years ago.
-Oxygen (O )2does not start to extensively accumulate in the atmosphere until 2.7 billion years ago.
-Eukaryotic cells make their first appearance on Earth around 2.2 billion years ago.
-Multi-cellular eukaryotes are introduced to Earth at around 1.4 billion years ago.
-It is around 600 million years ago that animals begin to take shape and some 150,000 years ago that
Homo sapiens calls the Earth home.
-The three major domains on Earth under which all organisms can be classified consist of: Prokarya
(prokaryotes), Archaea (prokaryotes), and Eukarya (eukaryotes).
-It is hypothesized that everything living on the Earth today can be categorized as a descendent of a
“Last Universal Common Ancestor” or LUCA, which was most likely a prokaryote.
- All organisms on planet Earth share:
Lipid membranes (phospholipids).
Deoxyribonucleic Acid (DNA) as a system for genetic information.
DNA to RNA to Protein as process of transferring information.
Common system of protein assembly (ribosomes, enzymes, tRNA, mRNA, etc.)
The presence of proteins
Adenosine triphosphate (ATP)
Glucose (C6H 12) 6
-The existence of LUCA does not in any way suggest that life evolved only once. Life may have evolved
many times, but such ancestors lacked one or more of the above organismal traits that LUCA must have
Life Developed Early On:
-Life evolved within 600 million years. This is a surprisingly short amount of time considering that planet
Earth needed immense time to cool down from its Primordial state and the fact that the geological time
record is much older than 600 million years. -Stromatolites, dated to around 3.5 billion years ago, are produced by microbial activity (cyanobacteria).
Stages Of Prebiotic Evolution:
-In order to pursue prebiotic evolution the following are requirements:
1. Abiotic Synthesis – a phenomenon by which living organisms are created from non-living
2. Heritable Information – The codes that make life possible by which organisms transmit to their
3. Formation of Cells – The ability to synthesize fundamental units of organismal life.
-The three stages of prebiotic evolution are as follows:
- Geophysical Stage: What was the composition of the Earth and its atmosphere?
- Chemical Stage: How could the building blocks of life be synthesized?
- Biological Stage: How did the building blocks organize into living cells?
-Of the three stages, it is only the Biological Stage that is still poorly understood.
The Geophysical Stage:
-On Primordial Earth, the early atmosphere contained: H O, H 2 CH 2 NH 4 and 3 S. 2
-The external energy sources that had a major impact on the Earth (with no ozone layer) and may have
possibly influenced the formation of life-providing molecules consisted of ultraviolet light and lightning.
-The early atmosphere can be described as a reducing atmosphere where the molecules can be reduced
from the donation of electron-rich sources such as hydrogen.
The Chemical Stage:
-Important monomers for the development of life-supporting polymers include: amino acids (proteins),
sugars (carbohydrates), and purines/pyrimidines (nucleotides).
-It is important to note that abiotic synthesis would not be possible on today’s Earth due to the presence
of molecular oxygen (O ).2
-Life may have formed near deep sea vents where mineral rich, hot gases are spewing on the bottom of
the ocean near the Earth’s mantle.
-A chiral molecule is one that is not superimposable on its image. Examples include two enantiomers,
handedness, and molecules with the same chemical and physical properties. -Thalidomide was developed as an anti-emetic drug for pregnant mothers. However babies that were
born were deformed at birth. This is because thalidomide can readily interconvert into teratogen (an
agent that causes birth defect