LESSON 1: EARTH: THE UNIQUE PLANET AND ITS SUBSYSTEMS
Life is the condition that distinguishes organisms from inorganic objects and dead organisms, being
manifested by growth through metabolism, reproduction, and the power of adaptation to environment through
changes originating internally. (Life | Definition of Life at Dictionary.com)
Sometimes, man's failure to protect the environment and LIFE here on EARTH is perhaps due to:
➢ Inability to recognize the full consequence of his or her actions; and
➢ Lack of appreciation of how truly unique the Earth is.
The Earth: A unique, habitable planet in the solar system
The solar system is composed of the sun and the eight major planets revolving around it. Among those
eight planets, only one can support life which is the Earth – the planet we live in. But the question is, how come
Earth can support life while the other planets cannot?
There are only two major requirements for a planet to become habitable.
1. The star should survive long enough for its planets to develop life which means a medium-mass star, such as
the sun, can survive long enough for life to develop.
(https://www.nationalgeographic.org/encyclopedia/sun/)
2. The planet must be located in the Goldilocks Zone – a region in the universe where water could remain liquid.
Different stars have different Goldilocks Zone, or habitable zones. Blue stars tend to have farther habitable zones
since they are relatively hotter and red stars have closer habitable zones since they are relatively cooler.
(https://www.forbes.com/sites/startswithabang/2020/01/13/could-therebe-life-on-the-first-earthsized-habitable-zone-planet-found-by-nasastess/#1b52efa27919 )
Being in the Goldilocks Zone indicates that due to the distance of Earth from the sun, the amount of heat and
solar energy received is just enough to make the temperature of Earth neither too hot nor too cold. As we all
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know, water evaporates if it is subjected to a very hot temperature and gets freezes if subjected to a very
cold temperature. The capability of early Earth to sustain liquid water dramatically increased the possibility
of life.
For the inner planets, Mercury and Venus, since they are too close to the sun, the solar energy received is
too much, contributing to the increase in temperature of their surfaces. For the other planets, such as Mars,
Jupiter, Saturn, Uranus, and Neptune, their distances from the sun are so far that the energy they receive is
very little, making these planets very cold.
Other factors for other planets to be inhabitable: (An earlier definition of inhabitable meant completely the
opposite: "not able to be lived in.)
Mercury, for example, experiences extreme temperatures due to its slow rotation. It also has a very thin
atmosphere that is not capable of capturing and maintaining the right amount of heat.
Venus, on the other hand, is very hot because it has a lot of active volcanoes that produce a very thick
atmosphere. The thick atmosphere contributes to an increased greenhouse effect, making the surface
temperature very high.
In contrast with Venus, the fourth terrestrial planet, Mars, has very little volcanic activity. As a result, it has
a thin atmosphere and cold surface temperature.
The Jovian planets (the four remaining gas giants), are mainly composed of gases. Therefore, there is no land
where organisms can live. With these features, it can be clearly seen how Earth is the only planet compatible
with life.
Scientists also believe that carbon and its unique properties are the basis of all life. Carbon has four valence
atoms, which enables it to easily bond with other carbon atoms and create long complex molecules and
polymers. Thus, the biological macromolecules such as lipids, carbohydrates, proteins, and nucleic acids all
have carbon atoms in their structure.
Knowing the requirements for the existence of life on a planet, scientists tried to determine how life started
on Earth. In 1952, Stanley Miller and Harold Urey conducted an experiment that replicated the conditions of
early Earth. They found out that life started in the oceans. During the extreme conditions of Earth, the
organisms that thrived were called extremophiles. These organisms were able to adapt to extreme
environment such as very high or very low temperatures, high acidity, or extreme pressure.
As seen in the Miller-Urey experiment, the early atmosphere did not contain oxygen gas. The presence of
oxygen first started when cyanobacteria emerged. Cyanobacteria were the first organisms that could produce
oxygen gas through photosynthesis. But the current oxygen levels of today, were not just due to the
cyanobacteria. It was only about 600 million years ago that the oxygen levels rose to its current levels.
Scientists, however, are still unsure as to what caused the oxygen levels to rise.
The Earth’s subsystems
1. Definition of a system:
➢ A set of interconnected components that are interacting to form a unified whole.
2. Components or subsystems of the Earth System:
➢ The arrows in the diagram below indicate the interaction among the components or subsystems of
the Earth System.
3. The Earth System is essentially a closed system. It receives energy from the sun and returns some of this
energy to space.
➢ A closed system is a system in which there is only an exchange of heat or energy and no exchange of
matter.
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(https://www.slideshare.net/maleigh/grade-11-earth-life-science-earthsystems-subsystems )
A. The Atmosphere
▪ The atmosphere is the thin gaseous layer that envelopes the geosphere.
▪ The present atmosphere is composed of 78% nitrogen, 21% oxygen, 0.9% argon, and small amount of other
gases.
▪ One of the most important processes by which the heat on the Earth’s surface is redistributed is through
atmospheric circulation.
▪ There is also constant exchange of heat and moisture between the atmosphere and the hydrosphere
through the hydrologic cycle or the water cycle which you just had encountered when you had labelling
activity a while ago.
http://ete.cet.edu/gcc/?/volcanoes_layers/
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B. The Geosphere (some references used the term Lithosphere)
▪ Beneath the atmosphere is the solid region of the Earth called geosphere.
▪ It does not only comprise the visible layer, it also extends to the center of the Earth.
▪ It has a depth of 6400 km, making it the largest sphere of Earth.
▪ It is divided into different layers: crust, mantle, outer core, and inner core.
▪ Misconception alert:
✓ The geosphere is a major sphere of earth that deals with the solid components, such as landforms,
rocks, and layers of Earth. It is not lithosphere. Lithosphere refers only to the crust and top portion of
the upper mantle.
(http://antioceanacidification.weebly.com/affects-on-geosphere.html)
C. The Hydrosphere
▪ About 78% of the Earth is covered with liquid water (hydrosphere) and much of it is in the form of ocean
water.
▪ Only 3% of Earth’s water is fresh: 2/3 are in the form of ice, and the remaining 1/3 is present in streams,
lakes, and groundwater.
▪ The oceans are important sinks for carbon dioxide through direct exchange with the atmosphere and
indirectly through the weathering (physical or chemical breakdown) of rocks.
▪ Heat is absorbed and redistributed on the surface of the Earth through ocean circulation.
(https://428213922994289719.weebly.com/hydrosphere.html )
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D. The Biosphere
▪ The biosphere is the set of all life forms on Earth.
▪ It includes all of the microbes, plants, and animals that can be found 1 km above sea level down to the
deepest parts of the oceans.
▪ It extends to any place where life of any kind might exist.
▪ For the majority of life on Earth, the base of food chain comprises photosynthetic organisms. During
photosynthesis, carbon dioxide is withdrawn from the atmosphere, while oxygen is released as a byproduct.
▪ The biosphere is a carbon dioxide sink, and therefore, an important part of the carbon cycle.
✓ Carbon cycle = is the process by which carbon is transferred among the atmosphere, oceans, soil, and
living organisms.
(https://www.shutterstock.com/image-vector/biosphere-vector-illustration-labeled-all-natural-1520499716 )
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