Geoscience Reference
In-Depth Information
C
OMMENTARY ON
F
IGURE
1.1.- The influx of evaporation into the
atmosphere is not compensated for and the planet is surrounded by a
very dense atmosphere mainly composed of carbon dioxide (CO
2
),
dinitrogen (N
2
) and gaseous water, resulting from gravitational
differentiation (the heaviest elements being concentrated as a core at
the heart of the geosphere). The greenhouse effect is enormous and an
ocean of water cannot form. This is the Earth's “Venus” phase.
1.2.4.
Why are there oceans on Earth and a “Venus inferno” on
Venus?
Earth and Venus are two neighboring telluric planets, formed at the
same time and of a very comparable size. How do we explain the fact
that the conditions on their surfaces and in their atmospheres are so
dissimilar today?
1
Aside from the conditions on their surfaces and the composition of
their atmospheres, two important characteristics distinguish the two
planets. First, there are no active plate tectonics on Venus, whereas
Earth maintains one. We can observe this in everyday life through
earthquakes, volcanic activity or, more poetically, through
contemplating our mountainous countryside. The second characteristic
is the presence of an important satellite, the Moon, which revolves
around the Earth. The Moon and the Earth have a very important mass
ratio (1/81), now known to us as the most important between two
planetary bodies in orbit around their common center of gravity
(which is naturally much closer to the center of the Earth than to the
center of the Moon). This duo resulted from a giant impact between
two planets in the process of formation just over 4.5 billion years ago.
Because of its kinetic conditions (notably speed and angle of
incidence), this impact threw out a very significant quantity of matter
into space while still preserving the core of the larger of the two
1 Remember the story that Venus, the morning star, was known to the Romans by the
name of Lucifer (carrier of light), whereas the Christian tradition ended by
transposing Lucifer, the angel dethroned after wanting to supplant his creator, into
Satan.
