Chapter 49: People and the Biosphere

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Chapter 49 People and the Biosphere

• Section 1 Human Population

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Human Population

• When humans formed permanent settlements, they
  began a long history of profoundly affecting the
  environment
• They made changes to the environment that were
  not easily undone
• Because people did not really understand how the
  natural environments on Earth functioned, they
  could not assess the effects of their activities
  on the environment
• For a long time, the human population was unaware
  that it was harming the world around it

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Human Population

• Over time, the human population has increased
  dramatically as has our knowledge of the
  Earths fragile environments
• Today we are more aware of how our actions affect
  our world
• But at the same time, we are also more capable of
  permanently damaging not just particular places
  on Earth but the entire biosphere itself

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Population Growth

• Many environmental problems seem large and urgent
  today because of the rapid increase in human
  population
• The huge numbers of humans on Earth are making
  enormous demands on the planet
• A population grows when the birthrate is greater
  then the deathrate
• Both of these must be taken into consideration
  when trying to understand the growth of the human
  population

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Birthrate

• Vary dramatically from one country to another
• In the US and much of Europe, the birthrate
  decreased during the 1970s
• In the 1980s, American birthrates rose slightly
• If current birthrates are maintained, our
  population will double in less than 100 years
• In some European countries, the growth rate is so
  low that populations are actually declining

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Birthrate

• The situation is quite different in other
  countries
• More than two thirds of the worlds population
  live in the tropical countries of Africa, South
  America, and Asia
• In some of these countries, the population
  continues to grow at an annual rate of about 3
• Although this rate of growth appears to be low,
  it will double the present population in only 23
  years

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Deathrate

• The deathrate has decreased worldwide
• Over the past few hundred years, changes in
  agriculture have made more and better foods
  available throughout the world
• Improvements in the quality and availability of
  medical care have wiped out many deadly diseases
  and contributed to an increase in the life span
  of the average person

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Effects of Human Population Growth

• A high birthrate, a low deathrate, and a longer
  lifespan all contribute to population growth
• As human populations grow, their effects on the
  environment also grow
• Countries with a rapidly growing population are
  often unable to produce enough food to satisfy
  the demand

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Effects of Human Population Growth

• Today, scientists worry about the destruction of
  tropical forests
• Such devastation seems to be a high price to pay
  for farmland that is productive for only a few
  short years
• In addition, many of these tropical forests are
  often cleared by burning
• The burning produces large amounts of carbon
  dioxide, which is added to our atmosphere

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Effects of Lifestyles

• It is not population growth alone that causes
  environmental problems
• After all, the rate of population growth in many
  industrial countries has actually slowed
• The lifestyle of a population also contributes to
  the extraordinary environmental demands made on
  the Earth

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Effects of Lifestyles

• The population of the US is a good example
• Population growth has stabilized at a low level
• We use more energy and natural resources than any
  other country in the world
• We own many consumer goods
• Most families have two or more cars
• Radios, TVs, etc. are staples of most modern
  homes

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Chapter 49 People and the Biosphere

• Section 2 Pollution

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Pollution

• Materials released into the environment fall into
  two categories biodegradable and
  nonbiodegradable
• Materials that can be degraded, or broken down,
  by microorganisms into the essential nutrients
  from which they were made are biodegradable
• Sewage, scraps of food
• Nonbiodegradable materials cannot be broken down
  by natural processes or are broken down only very
  slowly
• Glass, plastics and metals, chemicals
• Once these materials are released into the
  environment, they remain there for a long time
  sometimes forever

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A consumer society produces extremely large
quantities of wastes. However, some wastes can
prove useful. These automobiles are valuable for
the scrap metal they contain. And some household
wastes can be recycled for further use.
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Biological Magnification

• Sometimes pollutants affect the biosphere in ways
  no one expects
• Many primary producers pick up nonbiodegradable
  pollutants from the water
• They concentrate them and store them in their
  tissues
• When herbivores eat producers, they too
  concentrate and store these nonbiodegradable
  compounds in their tissues
• When carnivores eat herbivores, the compounds are
  further concentrated

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Biological Magnification

• At each step in a food chain, the compounds are
  concentrated more and more
• In other words, the amount of the compounds in
  each organism in a food chain increases
• This phenomenon is known as biological
  magnification
• Biological magnification occurs with many
  pesticides and industrial waste products

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If the plants in the pond in which this moose is
dining have been contaminated by toxic materials,
they may actually poison the moose. The
concentrations of toxic chemicals in the plants
will increase in the tissues of the moose.
The toxic chemicals DDT became part of many food
chains when it was widely used as a pesticide.
These falcon eggs show the dramatic effects of
DDT poisoning.
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Air Pollution

• The air supplies the oxygen our cells need to
  metabolize food and receives the waste products
  we give off as a result of our life processes
• But the air also contains many other
  chemicalschemicals that are not part of the
  natural composition of the atmosphere

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Smog

• If you live in a city, you may be familiar with
  the dirty-brown haze called smog
• Smog smoke fog
• Contains different pollutants in different places
• The causes of smog also differ from one location
  to another

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Smog

• Weather conditions called temperature inversions
  can make smog a serious health hazard
• Normally, cooler air is at higher altitudes than
  warmer air
• The warmer air closer to the Earths surface
  contains pollutants
• But because it is warm, it is less dense than
  cool air and rises
• As it rises, it slowly cools, and the pollutants
  it contains are carried away by winds

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Smog

• During an inversion, a layer of cool polluted air
  is trapped beneath a layer of warm air
• Because the cool air is denser than the warm air
  above it, it cannot rise
• As a result, the pollutants are kept near the
  ground
• Temperature inversions can last for hours, days,
  and even weeks

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The skyline of Los Angeles, California, is barely
visible through a curtain of smog. This city and
many others like it depend upon automobiles and
buses to move people from place to place. The
vehicles produce waste gases that contribute to
the formation of smog.
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Acid Rain

• Certain pollutants in the air combine with water
  vapor to form droplets of acid
• When these droplets fall to the Earth in rain,
  the rain is called acid rain
• In many areas, the coal and oil burned in
  factories and power plants to generate energy
  contain large amounts of sulfur
• When sulfur is burned, it forms sulfur dioxide
• Sulfur dioxide dissolves in water to form a
  strong acid sulfuric acid

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Acid Rain

• Sulfur dioxide is often carried on prevailing
  winds far from where it is produced
• The effects of acid rain on the environment are
  numerous and serious to life
• Acid rain damages plants, rivers, lakes, etc.

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Acid rain is a serious threat to the environment.
Its effects on forest trees can be seen in this
picture of evergreens that are now never green.
Their needles have been burned off the branches
by rains.
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The Greenhouse Effect

• The amount of carbon dioxide in the atmosphere is
  increasing as a result of human activity in the
  biosphere
• Carbon dioxide is produced when carbon-containing
  fuels are burned
• Carbon-containing fuels include wood and charcoal
  as well as fossil fuels such as coal, oil, and
  natural gas
• Over the years, the burning of trees and fossil
  fuels for energy has released vast quantities of
  carbon dioxide into the atmosphere

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The Greenhouse Effect

• Energy from the sun is absorbed by the Earth and
  changed into heat
• Later, this energy is radiated back from the
  Earth to the atmosphere
• Carbon dioxide and other gases in the atmosphere
  absorb this heat energy
• Greenhouse effect

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The Greenhouse Effect

• As levels of carbon dioxide in the air increase,
  more heat is absorbed and the temperature of the
  Earth increases
• The effects of this global warming are unclear
• Melting of the polar icecaps
• Major changes in agriculture

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Venus, although much like the Earth in many ways,
has an atmosphere that consists mostly of carbon
dioxide. As a result, Venus is considerably
hotter than Earth. Scientists are concerned that
the temperature of Earth will increase as levels
of carbon dioxide in the atmosphere increase. If
this happens, the huge polar ice caps will melt
and sea levels will rise, flooding many coastal
regions.
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Holes in the Ozone Layer

• A layer of ozone exists far above the Earth in a
  part of the atmosphere called the stratosphere
  (10 30 miles above the Earths surface)
• Protects the Earth from harmful ultraviolet
  radiation from the sun
• Without the protection of this layer, few living
  things could survive

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Holes in the Ozone Layer

• Scientists have recently discovered that the
  ozone layer is becoming thinner in certain places
  around the poles
• Holes in the ozone layer
• The major cause of ozone depletion is a form of
  chemical air pollution that results from the
  addition of chlorofluorocarbons to the air
• Scientists predict that if the amount of UV
  radiation that reaches the Earth increases, the
  frequency of certain diseasessuch as certain
  forms of skin cancerwill also increase

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In this image, areas of low ozone concentration
are in black/blue. The hole in the ozone layer
extends over Antarctica and part of South
America.
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Water Pollution

• In the United States, billions of liters of fresh
  water are used daily
• Drinking, cooking, bathing, cleaning
• Although water is a renewable resource, there is
  a limited amount of fresh water
• 75 of Earth is water
• Only 3 is fresh water
• Only a small portion is available for living
  things
• The greater portion is locked up in ice, mainly
  in polar ice caps and glaciers
• The most common sources of water pollution are
  chemical wastes, raw sewage, and high temperatures

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In many places in the world, the supply of
drinkable water is severely limited. Here in
Malawi, people fill buckets with water that is
pumped from a communal well. These heavy buckets
of water must be carried to their home.
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Chemical Contamination

• Toxic chemicals can pollute water in two ways
• The chemicals can enter into streams and rivers
• Chemical wastes discarded on land can seep
  through the ground and enter the ground water
  supply

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Sewage Contamination

• Sewage consists of large quantities of wastes
  that contain nitrogen compounds
• These compounds are used by bacteria in a process
  that requires oxygen
• If untreated sewage is added to rivers and
  streams, the number of bacteria increases
  dramatically
• These bacteria use up most of the available
  oxygen as they break down the nitrogen compounds
• Other organisms that live in the water may
  suffocate because their supply of oxygen is
  depleted

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Sewage Contamination

• In rural areas, where homes are far apart, sewage
  is usually treated in septic systems
• In a septic system, bacteria work on the sewage,
  reducing it to water that is nearly pure
• This water seeps out of the septic system and
  into the ground

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Sewage Contamination

• In cities, sewage must be treated in sewage
  treatment plants
• In special tanks, this sewage is broken down by
  bacteria
• Once the bacteria have decomposed the organic
  matter, chemicals that kill harmful
  microorganisms are added to the sewage and the
  treated water is released

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Sewage Contamination

• Human sewage also contains many potentially
  harmful microorganisms bacteria, viruses, and
  protozoa
• Filter-feeding organisms, such as clams and
  mussels, ingest the microorganisms and
  concentrate them in their tissues
• When these shellfish are eaten, diseases such as
  hepatitis, typhoid, and certain forms of
  dysentery can spread

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Although almost three quarters of the Earth is
covered by water, the supply of fresh water that
is available for human needs is limited. It is
extremely important to protect this water from
becoming polluted.
Many cities and towns have sewage-treatment
plants that process household waste water. In
huge outdoor tanks, water is treated by chemicals
and microorganisms.
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Thermal Pollution

• Many factories and power plants produce heat as a
  waste product
• In the past, water from nearby rivers, lakes, or
  the ocean was used to cool such plants
• The water was pumped through pipes in the cooling
  system, where it absorbed heat
• The heated water was then pumped back into the
  environment

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Thermal Pollution

• In some cases, heated water has no harmful
  effects on the ecosystem
• But often, heated water kills aquatic plants and
  animals
• This kind of water pollution is called thermal
  pollution

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Water is often used by industries as a coolant.
In this nuclear power plant, heated water is
returned to the river from which it was pumped,
causing a kind of pollution called thermal
pollution. Thermal pollution is a danger to some
forms of aquatic life.
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Ocean Pollution

• For centuries people have dumped their wastes
  into the oceans
• Too many people produce too much waste, a great
  deal of which is nonbiodegradable
• Plastics and other wastes dumped into the oceans
  may float around for months or even years
• Large cities continue to dump so much sewage into
  the oceans that it cannot be degraded quickly
  enough
• Often, some of this sewage washes up on beaches

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Ocean Pollution

• Pollution near the shore is a serious matter
• Some wastes dumped into the oceanssuch as
  containers of disposable medical itemswash back
  onto shore, threatening the health of beach-goers
• Other wastes remain at sea, posing a hazard to
  ocean life

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The solid wastes produced by consumer societies
are often dumped into the oceans. This is
devastating not only to ocean life, but also to
beach-goers.
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Oil Spills

• Regardless of the cause, once oil is spilled, it
  is difficult to remove
• Oil slicks are deadly to marine animals that
  swallow the toxic oil or become coated with it
• Toxic chemicals in oil often accumulate in those
  animals that are not killed immediately
• In most cases, these chemicals make the animal
  sterile
• Some of the chemicals that accumulate in animal
  tissue are potent carcinogens that may cause
  cancer in the people who eat them

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Chapter 49 People and the Biosphere

• Section 3 The Fate of the Earth

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The Fate of the Earth

• People have always relied upon plants and animals
  for food, clothing, and shelter
• The survival of humans and human society depends
  upon the survival of other organisms in the
  biosphere
• Today, the survival of many of these organisms is
  threatened

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Forests

• Wherever you live, your life is dependent upon
  forests in many ways
• Trees provide us with many essential products
• Wood is used to make everything from pencils to
  houses
• Trees are a vital part of many ecosystems
• The roots of trees keep the soil loose and at the
  same time hold it in place, allowing rainwater to
  penetrate the soil without washing it away

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Forests

• When forests are carelessly cut down, many
  important changes occur
• Soil structure changes
• Microorganisms die
• Many small plants and animals can no longer
  survive
• Heavy rains wash away topsoil
• Water table drops

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Forests

• Many of our countrys few remaining old forests
  are being cut down at an alarming rate
• In tropical countries, rain forests are being
  destroyed so rapidly that they may disappear
  completely in 60 years
• Fortunately, government officials became aware of
  the problems associated with forest destruction

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Forests

• Programs that plant new trees when old trees are
  cut down are called reforestation programs
• Vital to the health of the biosphere

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These trees are no match for a chainsaw. Once
cut, they will be used to make many consumer
products. A tiny tree will be placed in its
place.
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Endangered Species

• When an animal or plant species becomes so rare
  that it is threatened with extinction, it is
  called an endangered species
• Species become endangered in several ways
• Hunting
• Are able to live in only one type of habitat
• Today, one plant or animal species becomes
  extinct every hour

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Huge herds of bison roamed the Great Plains until
hunters brought these awesome animals to the
verge of extinction. Today, protected by strict
laws, herds of these animals once again roam.
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Why Save Endangered Species?

• Extinction is forever
• Many people feel that we have no right to cause
  the extinction of other species
• Scientists, biologists, activists, etc.
• But human needs are great, as are the demands on
  the ecosystem

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Other animals have not been as lucky as the
bison. The California condor is close to
extinction. Captive breeding programs aim to keep
this species alive. The black-footed ferret hunts
prairie dogs. The population of ferrets is so
small that their actual location in the wild is a
closely guarded secret. The desert pupfish lives
in small desert pools. If anything happens to its
delicate habitat, it too will be in real danger
of becoming extinct.
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Useful Products

• Many everyday foods, medicines, and industrial
  compounds come from wild plant and animal species
• Antibiotics, heart drugs, anticancer medications,
  painkillers, and other important medicines are
  derived from plants

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Useful Products

• No one knows the benefits that might be hidden in
  yet unknown plants that grow in tropical rain
  forests
• If these rain forests disappear, the potential
  contributions of their inhabitants to our society
  will also vanish
• Many animal species produce compounds that may
  prove important to human health
• Sponges
• Sea cucumbers
• Horseshoe crab

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Food from Plants

• Most of the worlds population obtains its food
  from crops grown on farms
• The crop plants grown in the US today are the
  results of generations of selective breeding
• When plant breeders develop a better variety, it
  is produced in enormous numbers and planted all
  over the country
• But planting a single variety can prove dangerous

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Food from Plants

• Genetically similar plants are susceptible to the
  same diseases
• In some cases, people maintain seeds of crop
  varieties that are no longer commercially grown
• The genetic material in these seeds may become
  important if new crop varieties are wiped out by
  disease
• In other cases, crop breeders are constantly at
  work developing new disease resistant strains of
  crop plants

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Food from Plants

• In many cases they cross crop plants with strains
  of wild plants that have more genetic variability
• So far, wild plants related to crop plants have
  provided the necessary new genes crop breeders
  want to introduce into already developed strains
  of crop plants
• Scientists all over the world regularly search
  for new wild species related to food crops
• But they face one serious problem the
  destruction of natural habitats will destroy yet
  undiscovered wild plants

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The tomato, eaten by many people, was once
thought to be poisonous. In the past, the tomato
grew in the wild. Today, the plant is commonly
grown in many gardens. Who can tell how many
other wild plants will be found in remote areas
and what uses these plants may serve?
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Chapter 49 People and the Biosphere

• Section 4 The Future of the Biosphere

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The Future of the Biosphere

• A lot of people agree that because Earth supplies
  us with all we need for life food, water, air,
  and natural resources we owe our planet the
  very best care possible
• In the past, people have treated Earth with
  neglect
• Today, attitudes are changing

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Actions for Conservation

• There are people in the world who love wild
  places, wild plants, and wild animals
• There are also many people who understand how
  important the health of the biosphere is to the
  health of all species, including humans
• These people work together to protect the
  environment in many different ways

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Actions for Conservation

• Towns, counties, states, the federal government,
  and conservancy groups have all purchased land
  that is to be set aside for conservation purposes
• The preservation of land habitats is one of the
  most important responsibilities we shall assume
  in the years ahead
• It is more difficult to conserve the resources in
  the ocean
• To conserve ocean species, the countries of the
  world must join together to protect the oceans
  and their inhabitants

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Actions for Conservation

• Sometimes people work together to protect a
  single species
• For example, sports fisherman on the east coast
  have formed a group called Stripers Unlimited
• A group that works to protect habitats important
  to the striped bass
• Larger organizations such as the Sierra Club,
  World Wildlife Fund, and Green peace work on a
  national and international level to protect the
  environment

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Difficult Decisions

• Cleaning up the environment and keeping it clean
  are not easy jobs
• Solid-waste disposal
• Sewage treatment plants
• Toxic waste

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Difficult Decisions

• In overwhelming numbers, Americans are expressing
  their fears for the future of planet Earth
• You must decide how important the environment is
  and whether you are willing to pay to keep it
  healthy