Lecture 27
Hydrosphere. Rocks.
Chapter 13.13  13.14, 14.1  14.5
• Earth’s Water Envelope
• Earth’s Surface Layer
• Types of Rocks
Hydrosphere
~70% of the Earth’s surface is covered by oceans and
connected seas, which are full of life.
Surface water evaporates and influences weather.
Water absorbs solar energy and distributes it around the
world.
Oceans are large basins bounded by continents.
An ocean bottom gradually slopes down to ~130m with an
average width of 65 km (varying from 1 to 1000 km).
This continental shelf turns into continental slope (down to
~2 km), which joins the abyssal plain via continental rise.
Oceans average depth is ~3.7 km.
Marianas Trenches – 11 km below the surface.
Ocean Currents
Two ways oceans affect climate:
• Store heat (the first few meters contain more heat than
the entire atmosphere).
• Surface currents, produced by friction of air and water.
Heat transfer between air and water can exceed the rate of
arriving solar energy at the Earth.
This is why continents are cooler in winters than coastal
regions and islands.
Surface currents are wind-driven and mostly parallel to
major wind streams and form equatorial current.
This current runs into South America in the Atlantics and
into the East Indies in the Pacific.
Ocean Currents
At each of the contacts the current divides into 2 parts.
One flows to the south, the other one to the north.
Then westerlies drive them eastward across the oceans.
This mechanism produces 4 large whirlpools.
The Gulf Stream
Gulf Stream is a warm current moving partly into the Gulf
of Mexico, partly straight north along the US eastern coast.
It splits on the European side: one part moves south and
completes the whirl, the other one moves into the Arctic
Ocean.
Gulf Stream makes climate of NW Europe milder.
Summary
Earth’s atmosphere was developed over a large period of
time and is hospitable for life due to the right distance
from the Sun.
Weather is mostly due to the large amount of vaporized
water and winds, which exist due to the planet rotation
and uneven distribution of continents and oceans.
Water in oceans generally follows the wind directions and
is affected by the current distribution of continents.
Crust
The outer layer of the solid Earth’s surface consists of
rocks and is called crust.
Crust is about 40 km deep.
Crust’s composition:
Oxygen - 46.6%
Silicon - 27.7%
Aluminum - 8.1%
Iron - 5.0%
Calcium - 3.6%
There almost no pure elements
in crust, they are bound in
compounds.
Compounds of silicon account
for 87% of the rock and soil of
the Earth’s crust.
Minerals
A mineral is a crystalline inorganic natural solid that has a
specific chemical composition.
Minerals have specific chemical formulas (e.g., CaCO3),
but are usually identified by other names (e.g., calcite).
Minerals made of the same compound may have different
properties.
Most minerals vary in composition, while composition of
chemical compounds is invariable.
Among ~4000 known minerals most a rare.
Properties of Minerals
Two important properties of minerals:
Crystal form  arrangement of atoms in certain geometric
patterns.
Cleavage  tendency of a substance to split along certain
plains, which are determined by arrangements of atoms.
Well-developed crystals are rare due to interference with
neighboring crystals.
Cleavage is not a characteristic property of all minerals.
Mica can be peeled apart in thin sheets, while quartz has
no cleavage at all.
Some Common Minerals
Quartz (SiO2): six-sided prisms and pyramids, no cleavage.
Used in jewelry, optical instruments, for making glass.
Feldspar (silicates of K, Al - orthoclase, and of Na, Ca, and
Al - plagioclase).
Rectangular crystals with cleavage in 2 directions.
Used in making porcelain and as a mild abrasive.
Mica. Two main varieties: white (a silicate of H, K, Al)
and black (a silicate of H, K, Al, Mg, Fe).
Very soft, used as insulator in electrical equipment.
Calcite (CaCO3)  hexagonal crystals, cleavage in 3
directions. Chief constituent of limestones and marbles.
Three Types of Rock
There are 3 types of rock according to their origin.
Igneous rocks - rocks cooled from a molten state.
Volcanic origin. 2/3 of rocks in crust are igneous.
Sedimentary rocks - materials derived from other rocks
and deposited by water, wind, or glacial ice.
Make 8% of the crust, but 3/4 of the surface rocks.
Metamorphic rocks - igneous or sedimentary rocks that
have been changed (metamorphosed) by heat and
pressure deep under the Earth’s surface.
Igneous Rocks
Appear in the form of irregular grains.
Principal minerals contain silicon: quartz, feldspar, mica.
If molten lava cools quickly, it forms natural glass called
obsidian.
Grain size in the igneous minerals contains information
about both the cooling rate and the cooling environment.
Fast cooling gives fine-grained rocks, which come to the
surface with lava and cool there.
Slow cooling gives coarse-grained rocks, which formed
beneath the surface and became exposed due to erosion.
Sedimentary Rocks
Sediments are deposited by water, wind, or ice, and become
rocks through the pressure of the overlying deposits.
The sedimentary rocks have nearly rounded grains that do
not grow, like crystals of igneous rocks.
There are two groups of sedimentary rocks: fragmental rocks
and (bio)chemical precipitates.
Fragmentals: conglomerate (wide variety of sizes), sandstone
(small grains), shale (soft rock, consolidated mud).
Precipitates: limestone (chemical precipitate or shell
fragments), chalk (loosely consolidated variety of limestone),
chert (microcrystalline quartz, used as tools by earlier people).
Metamorphic Rocks
Both igneous and sedimentary rocks can be changed under
high temperatures and pressures inside the Earth.
Some minerals become unstable and form new substances
by chemical reactions; others grow more as crystals.
Many metamorphic rocks show a property called foliation.
This is the arrangement of flat or elongated mineral grains
in parallel layers due to a high pressure in one direction.
Examples: Slate  produced at low temperatures from
shale, is harder that slate, and usually black or dark.
Schist  formed at high temperatures from shale or finegrained igneous rocks, has large visible grains.