Earth is 4.6 billion years old
Life originated 4 billion years ago
There is fossil evidence to show that life originated 3.5 billion years ago
Sediments of the ocean floor have lower levels of carbon-13 than expected meaning this may be due
to deposits of dead plants that take in and are made of mostly carbon-12
Early photosynthetic take CO2 from atmosphere and synthesize organic compounds
There is chemical evidence that shows life may have originated 3.9 billion years ago
A type of layered rock that is formed when microorganisms bind particles of sediment together, forming thin
They are the earliest conclusive evidence of life found in the fossilized remains of structures
Modern day stromatolites are formed by layered growth of cyanobacteria
It provides evidence of microbial activity during primitive earth
Banded iron and stromatolites are "biosignatures" what do we know about how life is
linked to their formation?
Cyanobacteria is what left these biosignatures and proves that primitive earth was anaerobic and lacked oxygen
and then O2 levels increased due to microbial activity, and that life originated about 4 billion years ago
Stromatolites provide the evidence of life originating about 4 bya based on geological evidence and dating of
fossilized remains of stromatolites
The banded iron on sedimentary rocks gave the evidence of primitive life once being heterotrophic and anaerobic,
where fermented pathways were used to extract energy from organic molecules such as water. When
cyanobacteria used H2O to get electrons for photosynthesis, the released Oxygen reacted with Iron in water
forming a red-coloured precipitate and overtime the excess oxygen accumulated in the environment and gave
evidence of increased O2 levels.
What are the four major developments that need to take place to make a living cell.
Geological stage - Earth/ atmosphere comp.
Chemical - life’s building blocks
Biological - organization into living cells
Three stages of prebiotic evolution, how much is known about each.
It contained a lot of water vapour, hydrogen gas, methane, carbon dioxide and ammonia allowing for a
lot of reduction (using the electrons from these molecules for other reactions) to occur. This in the end
allowed for the development of complex molecules
The primordial atmosphere was a reducing atmosphere
The current atmosphere is oxidizing because there is a much higher level of oxygen present in the
atmosphere, therefore, the formation of new complex molecules is not suited because Oxygen is an
oxidizing agent and takes electrons, instead of providing electrons, therefore making it difficult to form
complex molecules without sufficient electrons.
Conditions in the primordial atmosphere, why were they conducive to the development
Laboratory simulation of primordial earth's reducing atmosphere, put in place to prove how certain organic
molecules( amino acids, Urea etc.) were created under these early earth conditions.
Conditions created several abiotic molecules that are necessary for life today. It did not, however, show that
primordial atmosphere actually contained all these gases (Hydrogen, Methane, Ammonia etc.) needed to
form such complex molecules.
Volcanic analysis suggests that Earth was probably less reactive, containing gases such as Nitrogen, Carbon
monoxide, and Carbon dioxide. Regardless, laboratory experiments have shown that even with an
atmosphere such as the one suggested by the geologists, crucial building blocks of life can still form
COULD NOT EXPLAIN: how polymerization occurred, homochirality (L amino acids, D sugars) because it only
produced monomers and a racemic mixture (50% of each chiral molecule).
What was the Miller-Urey experiments. What did it show, didn't show.
What is chirality, why is it important. Homochirality