Geology Module 2 Reviewer
Geology Module 2 Reviewer
Geology Module 2 Reviewer
MANTLE
Mantle- (1) it is made of solid rock, and (2) it is hot.
- Scientists know that the mantle is made of rock based on evidence from
seismic waves, heat flow, and meteorites.
- The properties fit the ultramafic rock peridotite, which is made of the iron-
and magnesium-rich silicate minerals.
- Peridotite is rarely found at Earth’s surface.
- Scientists know that the mantle is extremely hot because of the heat flowing
outward from it and because of its physical properties.
- Heat flows in two different ways within the Earth: conduction and convection.
- Conduction is defined as the heat transfer that occurs through rapid collisions
of atoms, which can only happen if the material is solid. Heat flows from
warmer to cooler places until all are the same temperature. The mantle is hot
mostly because of heat conducted from the core.
Convection- is the process of a material that can move and flow may develop convection
currents.
- Convection in the mantle is the same as convection in a pot of water on a
stove. Convection currents within Earth’s mantle form as material near the
core heats up. As the core heats the bottom layer of mantle material, particles
move more rapidly, decreasing its density and causing it to rise. The rising
material begins the convection current. When the warm material reaches the
surface, it spreads horizontally. The material cools because it is no longer near
the core. It eventually becomes cool and dense enough to sink back down into
the mantle. At the bottom of the mantle, the material travels horizontally and
is heated by the core. It reaches the location where warm mantle material
rises, and the mantle convection cell is complete.
CORE
The Core At the planet’s center lies a dense metallic core.
- Scientists know that the core is metal for a few reasons. The density of Earth’s
surface layers is much less than the overall density of the planet, as calculated
from the planet’s rotation. If the surface layers are less dense than average,
then the interior must be denser than average. Calculations indicate that the
core is about 85 percent iron metal with nickel metal making up much of the
remaining 15 percent. Also, metallic meteorites are thought to be
representative of the core. If Earth’s core were not metal, the planet would not
have a magnetic field. Metals such as iron are magnetic, but rock, which
makes up the mantle and crust, is not. Scientists know that the OUTER CORE
IS LIQUID and the INNER CORE IS SOLID because S-waves stop at the
inner core. The strong magnetic field is caused by convection in the liquid
outer core. Convection currents in the outer core are due to heat from the even
hotter inner core. The heat that keeps the outer core from solidifying is
produced by the breakdown of radioactive elements in the inner core.
CONTINENTAL DRIFT
Alfred Wegener- continental drift hypothesis was developed in the early part of the 20th century
- Wegener said that continents move around on Earth’s surface and that they
were once joined together as a single supercontinent.
- That’s the true size and shape of a continent and many can be pieced together
like a puzzle. The easiest link is between the eastern Americas and western
Africa and Europe, but the rest can fit together too
- He proposed that the continents were once united into a single supercontinent
named PANGAEA, meaning all earth in ancient Greek. He suggested that
Pangaea broke up long ago and that the continents then moved to their current
positions.
- He called his hypothesis CONTINENTAL DRIFT.
Evidence for Continental Drift
Identical rocks of the same type and age are found on both sides of the Atlantic Ocean.
Mountain ranges with the same rock types, structures, and ages are now on opposite sides
of the Atlantic Ocean.
Ancient fossils of the same species of extinct plants and animals are found in rocks of the
same age but are on continents that are now widely separated He suggested that the
organisms would not have been able to travel across the oceans.
FOR EXAMPLE, the fossils of the seed fern Glossopteris were too heavy to be carried so
far by wind.
The reptile Mesosaurus could only swim in fresh water. was a swimming reptile but
could only swim in fresh water.
Cynognathus and Lystrosaurus were land reptiles and were unable to swim.
Grooves and rock deposits left by ancient glaciers are found today on different continents
very close to the equator. This would indicate that the glaciers either formed in the
middle of the ocean and/or covered most of the Earth. Today glaciers only form on land
and nearer the poles. Wegener thought that the glaciers were centered over the southern
land mass close to the South Pole and the continents moved to their present positions
later on. Coral reefs and coal-forming swamps are found in tropical and subtropical
environments, but ancient coal seams and coral reefs are found in locations where it is
much too cold today. Wegener suggested that these creatures were alive in warm climate
zones and that the fossils and coal later had drifted to new locations on the continents.
Although Wegener’s evidence was sound, most geologists at the time rejected his
hypothesis of continental drift. Scientists argued that there was no way to explain how
solid continents could plow through solid oceanic crust. Wegener’s idea was nearly
forgotten until technological advances presented even more evidence that the continents
moved and gave scientists the tools to develop a mechanism for Wegener’s drifting
continents
Magnetic Polarity on the Same Continent with Rocks of Different Ages
Puzzling new evidence came in the 1950s from studies on the Earth’s magnetic history.
Scientists used magnetometers, devices capable of measuring the magnetic field intensity, to
look at the magnetic properties of rocks in many locations. Geologists noted important things
about the magnetic polarity of different aged rocks on the same continent. Magnetite crystals in
fresh volcanic rocks point to the current magnetic north pole no matter what continent or where
on the continent the rocks are located. Older rocks that are the same age and are located on the
same continent point to the same location, but that location is not the current north magnetic
pole. Older rock that are of different ages do not point to the same locations or to the current
magnetic north pole. In other words, although the magnetite crystals were pointing to the
magnetic north pole, the location of the pole seemed to wander. Scientists were amazed to find
that the north magnetic pole changed location through time. There are three possible
explanations for this: 1) The continents remained fixed and the north magnetic pole moved. 2)
The north magnetic pole stood still and the continents moved, or 3) both the continents and the
north pole moved.
• Plate boundaries are the edges where two plates meet. Most geologic activities, including
volcanoes, earthquakes, and mountain building, take place at plate boundaries
• Divergent plate boundaries: the two plates move away from each other.
• Convergent plate boundaries: the two plates move towards each other.
• Transform plate boundaries: the two plates slip past each other.
Divergent Plate Boundaries Plates
- move apart at mid-ocean ridges where new seafloor forms.
- Between the two plates is a rift valley.
- Lava flows at the surface cool rapidly to become basalt, but deeper in the crust, magma
cools more slowly to form gabbro. So, the entire ridge system is made up of igneous rock that is
either extrusive or intrusive. Earthquakes are common at mid-ocean ridges since the movement
of magma and oceanic crust results in crustal shaking. The vast majority of mid-ocean ridges are
located deep below the sea.