located in island arc provinces or on the continental margins of the circum-Pacific
region. This number would have to be multiplied by 10,000 in order to have a
close estimation for the amount of recent volcanism on the sea floor.
Oceanic crust is brittle and easily broken, especially in the areas of extensive
fractures cutting 8–15 km deep within the lithosphere, as indicated by bathymetric
studies and from monitoring seismic epicenters around the World. Earthquakes are
a common phenomenon related to the readjustment of material during lithospheric
stress. The material discharged in the water column during undersea volcanic
eruptions such as helium, carbon dioxide and carbon monoxide, hydrogen, sulfur,
methane etc. are carried by currents and/or absorbed by marine organisms. This
volcanic discharge is of primary importance for determining the volcanic budget
of our planet. Certain primary compounds such as carbon, hydrogen, and oxygen
are the building blocks for a viable planet, which can support various life forms.
Also, these discharge products could be of assistance in many aspects of human
life. For example, if we consider the discovery that natural methane gas is seeping
out onto the sea floor through bottom sediment, this could be of great interest since
it is a large, new source of untapped energy. Because we have only limited
knowledge concerning our ocean, it is expected that scientists will make many
more new discoveries as sea floor exploration continues.
Mantle Convection Currents
Since its initial formation and subsequent cooling, our planet’s interior has been
transformed by means of convective currents of heat within the mantle. The heat
flow (convective currents) is affected by heat lost across cold boundary layers
inside the mantle and as well as through the lithosphere-crust sequences (outer
shell of the Earth) (Figs. 2.3, 2.8). The convection currents form ‘‘rivers’’ of
flowing matter and energy inside the mantle and will carry hotter and more viscous
material towards the surface. The force driving this phenomenon of mantle convection is primarily due to the downward pull of gravity on the cold and dense
lithosphere and the upward motion of hotter matter rising to the Earth’s surface.
The increase of temperature with depth has been calculated to be about
20–25 °C/km below the plate boundary regions. The difference in temperature
combined with the effect of density differences in the mantle is responsible for
generating convection currents. The core-mantle boundary is about
3,500–3,700 °C, while the upper mantle-lithosphere is \1,000 °C. The convective
flows inside our planet are comparable to what happens in the atmosphere where
air currents are formed when an upward movement of hot air and a downward
movement of cold air take place. Because of the constant changes inside the
interior of the Earth, nothing has remained the same since the early formation of
our planet. Convection currents are the driving force for generating various processes such as plate motion and mountain building.
44
2 Our Haven, Planet Earth
region. This number would have to be multiplied by 10,000 in order to have a
close estimation for the amount of recent volcanism on the sea floor.
Oceanic crust is brittle and easily broken, especially in the areas of extensive
fractures cutting 8–15 km deep within the lithosphere, as indicated by bathymetric
studies and from monitoring seismic epicenters around the World. Earthquakes are
a common phenomenon related to the readjustment of material during lithospheric
stress. The material discharged in the water column during undersea volcanic
eruptions such as helium, carbon dioxide and carbon monoxide, hydrogen, sulfur,
methane etc. are carried by currents and/or absorbed by marine organisms. This
volcanic discharge is of primary importance for determining the volcanic budget
of our planet. Certain primary compounds such as carbon, hydrogen, and oxygen
are the building blocks for a viable planet, which can support various life forms.
Also, these discharge products could be of assistance in many aspects of human
life. For example, if we consider the discovery that natural methane gas is seeping
out onto the sea floor through bottom sediment, this could be of great interest since
it is a large, new source of untapped energy. Because we have only limited
knowledge concerning our ocean, it is expected that scientists will make many
more new discoveries as sea floor exploration continues.
Mantle Convection Currents
Since its initial formation and subsequent cooling, our planet’s interior has been
transformed by means of convective currents of heat within the mantle. The heat
flow (convective currents) is affected by heat lost across cold boundary layers
inside the mantle and as well as through the lithosphere-crust sequences (outer
shell of the Earth) (Figs. 2.3, 2.8). The convection currents form ‘‘rivers’’ of
flowing matter and energy inside the mantle and will carry hotter and more viscous
material towards the surface. The force driving this phenomenon of mantle convection is primarily due to the downward pull of gravity on the cold and dense
lithosphere and the upward motion of hotter matter rising to the Earth’s surface.
The increase of temperature with depth has been calculated to be about
20–25 °C/km below the plate boundary regions. The difference in temperature
combined with the effect of density differences in the mantle is responsible for
generating convection currents. The core-mantle boundary is about
3,500–3,700 °C, while the upper mantle-lithosphere is \1,000 °C. The convective
flows inside our planet are comparable to what happens in the atmosphere where
air currents are formed when an upward movement of hot air and a downward
movement of cold air take place. Because of the constant changes inside the
interior of the Earth, nothing has remained the same since the early formation of
our planet. Convection currents are the driving force for generating various processes such as plate motion and mountain building.
44
2 Our Haven, Planet Earth