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Lecture 12

GLGY 307 Lecture Notes - Lecture 12: Purple Bacteria, Pilbara Craton, Petrifaction

Course Code
GLGY 307
M.Dan Georgescu

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Early Earth Events
Four major processes happened in the proximity of the early Earth surface, and
all of them will influence the environment in which the life emerged on our planet
1. Early Crust Formation happened due to the differences in the temperature
between the very hot early Earth and the cold outer space; once the early
curst was formed the heat remained trapped at the Earth interior, where
the temperature remained trapped at the Earth interior, where the
temperature is approximately equal to that at the surface of the Sun.
Volcanic phenomena were common at the early Earth surface.
2. Early Atmosphere Formation as a result of the mixture of gasses from two
sources: those remnants from the Solar System formation and the new
ones resulted through the outgassing processes during volcanic
3. Ocean Formation happened early in the history of Earth through the
accumulation of water resulted from the vapor condensation. The zircon
minerals from Australia, which gave radiometric ages of circa 4.4 billion
years, require significant amounts of water.
4. A Catastrophic Meteorite Bombardment is documented in the early history
of the celestial bodies from the inner Solar System. The effects of this
process can be seen at the surface of the Moon, Mercury, and Mars; the
surface of these celestial bodies was not affected by plate tectonics, and
therefore the craters resulted from the meteorite impacts are still visible.
This is not the case of the Earth where the plate tectonics obliterated the
vestiges of this catastrophic series of events in the Solar System;
however, we can infer from the data from the Moon, Mercury and Mars
that this meteorite bombardment happened in the interval between 4.2
and 3.95 billion years ago. (b/w Hadean, and Archean times)
Oldest Organic Matter
The evidence of the chemical and biochemical phases of evolution are hard to
find in the rock record mostly due to the fact that molecules do not fossilize.
Despite this, an interesting discovery that came from the metamorphosed
sedimentary rocks (3.7 -3.8 billion years old) of the Isua Formation of the
southwestern Greenland comes to demonstrate the validity of our experiments
and assumptions of the chemical and biochemical evolution of life on Earth
These rocks have a dark appearance, which indicate that they deposited in a
reducing environment
Small-sized calcite minerals are disseminated within the rocks, and this
demonstrates that molecular oxygen existed only in small amounts, so true
layers of calcitic rocks could not form.
Isua Formation
Thin layers of graphite occur in these rocks; as the graphite is the final product of
the organic matter transformation in the subsurface conditions during the burial
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