Earth and Life Science
Topic 1: THE EARTH AS A UNIQUE PLANET
1.
Our location is far from many hazards.
The solar system sits far from the galactic core (almost 30,000 light-years), between two major
spiral arms. More so, the solar system's circular orbit helps it avoid that dangerous part of the
galaxy. The galactic core likely contains a massive black hole and releases consistent bursts
of radiation. Also, there are relatively few stars near the sun, reducing risks to Earth from
gravitational tugs, gamma-ray bursts, or collapsing stars called supernovae. The presence of
our big brother planet, Jupiter, farther out in the solar system blocking Earth from much of the
incoming debris, has also helped Earth become a safe haven for life. Jupiter acts like a giant
broom, sweeping the solar system of debris rocks as small as cars and as huge as moons that
could snuff out life in one fatal blow.
2.
Our sun is a stable and long-lasting star.
Our sun is a yellow dwarf, a relatively rare type of star that is both small and stable. It also has
a long life and probably would not start to fizzle out for another five billion years or so. Stars
more massive than the sun burn hotter and usually do not live long enough for planets to
develop life. Less massive, younger stars are often unstable and are prone to blasting their
planets with bursts of radiation. The sun radiates light and heat, or solar energy, which makes
it possible for life to exist on Earth. The sun provides the earth with energy estimated at over
239 trillion horsepower, about 35,000 horsepower for each current resident. Plants need
sunlight to grow. Animals, including humans, need plants for food and the oxygen they
produce. Without heat from the sun, Earth would freeze. There would be no winds, ocean
currents, or clouds to transport water.
3.
We are at just the right distance from the sun.
Earth is at an average distance of 93 million miles or 150 million kilometers away from the sun.
It orbits in the so-called Goldilocks zone, where the planet receives enough energy to allow
water to exist as a liquid on its surface. Too far, and the vital compound stays locked up as
ice. Too close, and the water would rapidly evaporate into the atmosphere. The Earth is the
only planet with huge bodies of water—70% of its surface area consists of oceans, lakes, and
seas surrounding huge bodies of land. Water is unique because it absorbs large amounts of
heat without much alteration in its temperature. Its absorption speed is extremely rapid—
about ten times as fast as steel. During the day, the seas rapidly soak up a great deal of heat,
thus the Earth stays fairly cool. At night, the oceans release the vast amounts of heat that they
soaked up during the day, which combined with atmospheric effects, keeps the surface from
getting too cold at night. If it were not for the tremendous amount of water on Earth, there
would be far greater day and night temperature variations. Many parts of the surface would
be hot enough to boil water in the day and the same part would be cold enough to freeze
water at night. Water is an excellent temperature stabilizer. The large oceans on Earth are a
vital part of our survival!
4.
We have the right stuff to host a dynamic core.
The interstellar cloud of gas and dust that gave rise to Earth contained enough radioactive
elements (potassium, uranium and thorium) to power a churning core for billions of years. This
creates a magnetic field which is crucial to life on our planet because it protects the planet
from dangers like solar flares and solar wind. The Earth's magnetic field serves to deflect most
of the solar wind, whose charged particles would otherwise strip away the ozone layer that
protects the Earth and the life on it from harmful ultraviolet radiation.
5.
We have a big moon to stabilize our axial wobble.
The Earth has a slight tilt and teeters like a top as it spins, which can cause drastic shifts in
climate over the course of thousands of years. But because of the moon's stabilizing effect
on our orbit, our climate is a lot steadier. Plus, the moon causes the tides, so if the Moon were
much nearer to the Earth, say 20 times closer, it would exert a gravitational force 400 times
greater than what we are used to. It would result to huge tides which would overflow onto
the lowlands, causing great flooding.
6.
We have an ozone layer to block harmful ray.
Ancient plantlike organisms in the oceans added oxygen to the atmosphere and created a
high-altitude layer of ozone that shielded early land species from lethal radiation. Ozone (O3)
is a gas in the atmosphere that protects everything living on the Earth from harmful ultraviolet
(UV) rays from the sun. Without the layer of ozone in the atmosphere, it would be very difficult
for anything to survive on the surface. Plants cannot live and grow in heavy ultraviolet
radiation, nor can the plankton that serve as food for most of the ocean life. The ozone layer
acts as a shield to absorb the UV rays, and keep them from doing damage at the Earth's
surface. The mixture of gases found in the atmosphere, without man's pollution, is perfect for
life. Nitrogen accounts for 78% of the atmosphere, oxygen 21% and argon 0.9%. Greenhouse
gases like carbon dioxide, nitrous oxides, and methane are trace gases that account for
about a tenth of one percent of the atmosphere. These gases trap the sun’s heat to keep the
planet warm. If it were much different, life would cease to exist on Earth. If our atmosphere
were thinner, many of the millions of meteors which now are burned up would reach the
Earth's surface, causing death, destruction and fires everywhere.
Topic 2: The Earth’s subsystems
The Earth has become so perfect for living organisms because of its interacting physical,
chemical and biological processes called Earth system. The Earth system is a set of all matter
both living and non-living, energy, and processes within Earth’s boundary. It is powered by
energy from two major sources: the sun and the planet’s internal heat. This enables numerous
processes and cycles to take place. Scientists break down Earth’s major system into four
subsystems (also called spheres) such as, the lithosphere/geosphere (land), hydrosphere
(water), biosphere (life), and atmosphere (air). These subsystems work together to influence
the climate, trigger geological processes, affect life all over the earth.
Interactions in Earth’s Spheres
Although the four systems have their unique identities, they are closely connected. For
example, many birds (biosphere) fly through the air (atmosphere), while water (hydrosphere)
flows through the soil (geosphere). These close connections cause changes to take place in
Earths spheres. These changes are called events. This two-way relationship between event
and sphere is called interactions. Below are some examples of events and the interactions
that happen.
Volcano. Volcanoes in the geosphere may cause profound direct and indirect effects on the
hydrosphere, atmosphere and biosphere. This happens when volcanoes (geosphere) emit
large amount of particulate matter into the air (atmosphere). These particles serve as nuclei
for the formation of water droplets (hydrosphere). Rainfall (hydrosphere) often increases often
increases following an eruption, stimulating plat growth (biosphere).
Acid Rain. Acid rain is any form of liquid precipitation (hydrosphere) that contains high level
of nitric and sulfuric acid. Rain (hydrosphere) brings these acids to the Earth, acidifying soil
(geosphere) lakes and rivers (hydrosphere). Acidic water leaches nutrients from the soil
(geosphere) into the water table (hydrosphere, making the soil less fertile for the
plants(biosphere) and the subterranean water (hydrosphere) not potable for humans
(biosphere).
Forest Fire. Forest fire (an event in biosphere) may destroy all the plants (biosphere) in the
area. This could lead to increase in erosion (geosphere). Increased amount of soil entering
the streams (hydrosphere) can lead to increased turbidity or muddiness of the water which
will affect that plants and animals (biosphere) that live in it.
Topic 3: Rock Forming Minerals
Minerals are inorganic substances that
are
naturally
occurring
in
the
environment. They have a specific
chemical composition. Molecules in a
mineral are arranged in a repeated
structure that form a solid crystal. These
molecules are composed of atoms of
certain
elements
that
are
held
together by chemical bond. The kind
and amount of elements present in a
mineral
affect
its
physical
and
chemical properties. Table 1 shows the elements that comprise almost 99 % of rock-forming
minerals.
Properties of Minerals
The chemical properties of minerals comprise their chemical composition. Gold is made up
of only gold atoms and diamond is only made up of carbon atoms. But most minerals are
made up of chemical compounds and each of them has a unique chemical formula. For
example, quartz is a silicate mineral composed of two oxygen atoms bonded with a silicon
dioxide (SiO2) while feldspar is a silicate of aluminum plus any of the elements sodium,
potassium, iron, calcium, or barium or their combinations. The basic building block for all
silicate minerals is the anion silica, SiO4.
Table 2 gives the seven categories of minerals based on their chemical composition. Minerals
within the same group may exhibit similar characteristics.
The chemical composition of minerals is expressed in their physical properties which are used
to identify them. These physical properties are given below:
1.
Color and streak
Every mineral has its own distinctive color. However, color alone is not enough to identify a
mineral correctly because some minerals may have similar colors. A more reliable test is the
streak test. This test is done by rubbing a mineral against a piece of porcelain. Streak is the
color given by a mineral in its powder form
2.
Luster
The property of a mineral to reflect
light is given by its luster. Mineral luster
can be metallic or non-metallic.
Metallic luster can be compared to
the shine of a polished metal. Nonmetallic luster can be described as
dull, pearly, silky, greasy or glassy.
3.
Hardness
Hardness is the resistance of a mineral
to scratching. The Mohs Scale of
Hardness describes the hardness of
some common mineral in a 1 to 10
scale.
To
identify
a
mineral,
its
hardness is usually compared with
that of common objects of known
hardness in the Mohs Scale as shown
in Table 5.
4.
Density and Specific gravity
Density describes the amount of matter present in a certain amount of space or volume. To
get mineral density, the mass of a sample is taken using a scale and the volume is determined
through the water displacement method. The density is then calculated by dividing the mass
by the volume of water displaced. Specific gravity is a measure of a mineral’s density as
compared to water. It is calculated by dividing the density of a mineral by the density of
water. A mineral with a specific gravity of 2 is twice as dense as water.
5.
Crystal habit and form
Crystal habit is the growth pattern exhibited by mineral crystals while crystal form is the
external shape of a mineral. Some common crystal habits are cube or cubic, prismatic,
bladed, tabular, radial, botryoidal, fibrous and dendritic. Figure 2 shows the characteristic
appearance of these crystal habits and forms.
6.
Cleavage and fracture
The tendency of a mineral to break along layers of weak points that form flat surfaces is called
cleavage. Fracture refers to the chipping shape of a mineral when broken.
The quality of cleavage are categorized into the following:
a.
Perfect – Mineral cleaves without leaving any rough surfaces forming full flat planes.
b.
Good – Mineral cleaves into smooth surfaces but with some rough edges.
c.
Poor – Cleavage is generally characterized by rough surfaces.
d.
Indiscernible or indistinct – Cleavage is hardly noticeable.
e.
None – Mineral never exhibit any cleavage. Broken surfaces are fractured and rough
7.
Diaphaneity
Also known as transparency, diaphaneity is the degree by which the mineral transmit light. It
can be described as opaque, translucent or transparent.
a.
Opaque – The mineral does not transmit light.
b.
Translucent – The mineral allows some amount of light to pass through it in a distorted
fashion.
c.
Transparent – The mineral allows transmission of light in an undisturbed manner.
All the properties discussed above are helpful in identifying minerals. The table below
summarizes the observable properties of some common minerals.
Common Rock-forming Minerals
Although there are around 5000 different mineral species, only a few form rocks and are
called “rock-forming minerals”. Most minerals are “accessory minerals” that occur in small
quantities within a rock. The common rock-forming minerals are plagioclase feldspars, alkali
feldspar, quartz, amphiboles, micas, olivine, pyroxenes, calcite and dolomite.
1.
Plagioclase feldspar
Plagioclase feldspar is a group of silicate feldspar minerals that are rich in sodium or calcium.
These minerals form a solid solution series ranging from pure albite, Na(AlSi3O8), to pure
anorthite, Ca(Al2Si2O8). Their color is usually white to gray with vitreous luster. Their hardness is
6 to 6.5 in the Mohs Scale. Specific gravity is between 2.5 to 2.8. Crystals are stubby prisms
and have perfect cleavage. Plagioclase feldspar is the most common rock-forming mineral.
It is found in most igneous rocks including granite, diorite, gabbro and basalt. It is an important
constituent of many metamorphic rocks such as gneiss. Plagioclase feldspar are used in
ceramic products, as fillers in paints, plastics and rubber and as gemstones.
2.
Alkali feldspar
Alkali feldspar is another group of silicate feldspar minerals. Minerals under this group are rich
in alkali metal ions. Their composition ranges between NaAlSi3O8 and KAlSi3O8. They are
commonly pink to white in color, with vitreous luster and perfect cleavage. Alkali feldspars
are very abundant in alkali and acidic igneous rocks like syenites, granites, and granodiorites.
Alkali feldspar is used to manufacture glass and ceramics and are sometimes used as
gemstones.
3.
Quartz
The third largest group of rock-forming minerals is quartz. It is made up of silicon dioxide (SiO2).
Pure quartz is colorless but can have variations in color due to impurities. It has a white streak
and vitreous luster. Its crystals are usually hexagonal and prismatic. Its hardness is 7 and
specific gravity is 2.65. Quartz is one of the most abundant minerals. It is found in many
metamorphic, sedimentary and igneous rocks that are high in silica such as granites and
rhyolites. Quartz is used in making glass, abrasive, foundry sand, hydraulic fracturing proppant
and as gemstones.
4.
Mica
Mica is a collection of hydrous potassium, aluminum silicate minerals. It has a variety of colors
that ranges from light to dark. It can be colorless, rosy, purple, silver, gray, dark green, brown
or black. Its luster is described as splendent but some appear pearly. Its hardness is 2.5 – 4.
Specific gravity varies with composition at 2.76 to 3.2. It cleaves perfectly into thin elastic
sheets. Mica is among the most important rock-forming minerals. It is found in all rock types –
igneous, sedimentary and metamorphic. Mica is largely used in the electrical industry as
capacitors.
5.
Amphiboles
Amphiboles are also silicate minerals. They are generally black or brown in color but can also
be dark green, white, gray, colorless or pale green. They have a white streak and vitreous
luster. Their hardness is about 5-6. Crystal habit can be columnar to fibrous to granular.
Amphiboles are component of many igneous and metamorphic rocks. Amphiboles are used
in construction as paving stones and as a veneer or facing on buildings, as crushed stone for
road and railroad bed.
6.
Pyroxene
Pyroxene minerals belong to the silicate group that generally contain magnesium, iron,
calcium and aluminum. They are usually dark brown or black but some occur in a wide range
of colors. They have white streak and vitreous to dull luster. Their hardness is 5 to 7 while
specific gravity is 3 to 4. Their cleavage often have nearly square cross-section
Pyroxenes are found in igneous and metamorphic rocks throughout the world. Pyroxenes are
used as crushed stone and dimension stones, as gem materials,
and as an important source of lithium.
7.
Olivine
Another group of silicate minerals is olivine. Their chemical composition range between
Mg2SiO4 and Fe2SiO4. They are usually green in color but can be yellow- green, bright green,
brownish-green or brown. They have colorless streak and vitreous luster. Their hardness ranges
from 6.5 – 7. Specific gravity is 3.2 to 4.4. They exhibit poor cleavage and brittle with
conchoidal fracture. Olivine is typically found in igneous rocks such as basalt, gabbro and
peridotite. Olivine is commonly used as a gemstones.
8.
Calcite
Calcite is a rock-forming mineral from the carbonate group. Its chemical formula is CaCO3.
It is usually white but can also occur as colorless, gray, red, green, blue, yellow, brown or
orange. It has a white streak and vitreous luster. Its hardness is 3 and specific gravity is 2.7. It
cleaves perfectly into three directions. Calcite is found everywhere in sedimentary,
metamorphic and igneous rocks. It is a principal component of limestone and marble which
make up a good portion of the crust. Calcite is used as an acid neutralizer, a low-hardness
abrasive and a soil conditioner.
9.
Dolomite
Dolomite is a calcium magnesium carbonate with a chemical composition of CaMg(CO3)2.
Its color can be colorless, white, pink, green, gray, brown or black. It has a white streak and
a vitreous to pearly luster. Its hardness is 3.5 to 4 at Mohs Scale. Its specific gravity is 2.8 to 2.9.
It has a perfect cleavage. Dolomite is a primary component of the sedimentary rock
dolostone, of the metamorphic rock dolomitic marble and of the sedimentary rock dolomitic
limestone. Dolomite is useful as construction aggregate. It is a source of magnesia for the
chemical industry and agricultural soil treatments.