Student project submitted June 2000

 

How does the Earth’s history affect our environment – past, present and future?

 

How does the Earth's history affect our environment - past, present and future?
This diagram created using Inspiration® by Inspiration Software, Inc.

 

Changing Environments

 

From the time of the “Big Bang” until the present, the Earth has gone through many changes that have affected its environment.  During prehistoric time, when Earth’s continents were joined as one huge landmass, many of the changes that occurred to our young planet were due to changes in the atmosphere causing climatic variations.  At the same time, geologic changes such as earthquakes and volcanic eruptions were also making contributions to the newly developing Earth. Consequently, in the evolutionary process, many of these changes lead to the development of new species of plants and animals, while other species faded away when the environment that they were accustomed to no longer existed.  Today, we are still evolving although it may not be as evident since it is a very slow process; nevertheless, what does the future hold for Earth and the species that inhabit this planet now?  What can we learn from the Earth’s past that we can apply to the future?  What will assure us that future generations will have a nurturing environment in which to live, or will history repeat itself? Will we, like the dinosaurs become extinct due to our own ignorance or lack of concern for the environment that sustains our lives? Perhaps understanding the environmental changes of the past will better equip us to manage environmental issues in the future.

 

In the beginning, Earth was a very hostile setting. In fact, it was such a hostile place that it is difficult to believe that the Earth that we know today could have arisen from such a hellish environment. At that time, as the Earth was forming into a solid mass, and beginning to cool externally, there were many volcanic eruptions that emitted gases, such as hydrogen, nitrogen, and carbon dioxide, into a mostly anaerobic (without oxygen) atmosphere. At the same time, cyanobacteria were beginning to photosynthesize, producing oxygen as a byproduct. As a result, the oxygen that was being produced could react in three ways: First, with other substances emitted into the atmosphere such as volcanic gases;  second, with minerals such as iron; or third, it could be utilized by aerobic orgasms (Johnson and Stucky, 22).   However, all these things working together kept oxygen from building up heavily in the atmosphere. Later, as a crude atmosphere began to form from condensation, and after the atmosphere had finally accumulated enough moisture to form precipitation, the iron and oxygen that mingled there were released in the rain. Consequently, a layer of rust particles drifted to the bottom of the ancient sea that covered Earth during the Precambrian.  A remnant of this is seen in the Abilene, Texas landscape  where the soil is a bright, rusty, red color. The red shale, clay, and sandstone of this area are possibly due to the precipitation of iron oxides that were formed during the Precambrian era, and exposed during the Permian as a result of erosion. Therefore, after these events, there was nothing preventing the build up of oxygen in the atmosphere. Once water condensation occurred, the resulting rain filled the low areas of Earth with water thus forming bodies of water such as oceans.  Now as a result, new species could evolve because oxygen molecules were available, held between the water molecules.

 

Consequently, the proscenium was set for life to begin in an aerobic atmosphere. In conjunction with plate tectonic movement, which allowed the upper crust of the Earth to begin to separate, earthquakes released pressure built up from heat within the Earth’s core, and continued volcanic lava flows, lead eventually to one huge land mass called Pangea. At the same time, chemicals were released and a crude environment began to form from condensation. Additionally, negative and positive ions in the atmosphere produced lightening which provided the Earth with various chemicals necessary to produce amino acids.  Chemicals such as phosphorus, phosphates, and nitrogen bases began bonding with these amino acids to produce DNA (deoxyribonucleic acids) …the “blueprint of life” for all living things on Earth.  Finally, after millions of years have come and gone, and a rich environment has developed to protect the Earth from the harsh, damaging, inferred rays from the sun, after all the tectonic folding, after many pyrotechnics (volcanic eruptions) and abyssal intrusions, the very first organisms of life appeared…the bacteria.

 

The first bacteria, Archaebacteria, were very simple prokaryotic cells, which thrived in the strange, chemically rich, anaerobic environment. Soon these bacteria evolved into mutual symbiotic relationships with other bacteria and the birth of the eukaryotic cell began.  The second group of bacteria known as Eubacteria is one of the most abundant bacteria on Earth.  Scientists, however, believe that cyanobacteria were the early ancestors of plants because they had chlorophyll that is responsible for giving plants their green coloring.  Equally important, chlorophyll plays an important role in photosynthesis, which is a process in which a plant converts sunlight, combined with carbon dioxide, water from the environment and nutrients from the soil to make sugar that the plant can use as energy.

 

Early plant life first developed in the ocean waters; however, as time marched on and competition for life became difficult in the crowded seas, plants began to move onto the Earth’s land surface.   In addition, plants had to go through many changes in order to make this important move.  They had to change their body structure to keep from drying out as terrestrial organisms.  The very first plants were non-vascular plants such as mosses, liverworts, and Cooks Sonia, which crept onto the barren land.  Then when the environment became crowded once again, the plants evolved a bit more by developing roots, leaves, and stems to help them reach above other plants to the sun’s nurturing light.  The roots anchored the plants into the soil and provided nutrients and water while the stems developed vascular tissue called xylem and phloem to carry the water and nutrients to all parts of the plant.  This is one of the most important evolutionary changes to ever take place on Earth because photosynthesis is responsible for using carbon dioxide from the Earth’s atmosphere and giving off oxygen as a by product.  Most people don’t realize that terrestrial plants produce fifty percent of the world’s oxygen and the other fifty percent of the Earth’s oxygen is made from the great kelp forest in the ocean.  Without plants all oxygen-breathing organisms would die.

 

During the Mesozoic a huge, inland, Cretaceous sea divided the North American continent in half, covering much of Central and Western Texas.  It is during this time that the Balcones Fault Zone developed, which was once the edge of the Gulf of Mexico. This fault runs northeast from San Antonio through Austin to Dallas and is the remnants of an eroded prehistoric mountain range called the Ouachita Range (Sheldon, 13).

The major groups of vascular plants during that time were the Trimerophyton (ferns, and Horsetails) which appeared in the Devonian.  Still later, a major group called the conifers, which are cone-bearing plants, made their début along with such plants as Cycads and Ginkos.  This time period became known as the Carboniferous.  Much of Texas’ “Black Gold” was made during this time.  Large amounts of plant remains were deposited along with mud and sand into the sea that then covered most of Texas.  As a result, deltas formed in the area that is now Balcones Fault. As the Ouachita Mountains were uplifted, the area west of these mountains began to sink forming deep basins in which deep areas of limestone collected from nearby ranges. Finally, the Earth belched one last time in Texas raising the Cretaceous rocks approximately 2,000 feet above sea level.  This upraising is responsible the Edwards Plateau formation which marks the Balcones Fault zone (Spearing, 17).  Also, much of North Texas’ gas was produced during this time period. As the seas receded and dried only one huge inland sea remained in far west Texas.  Eventually, these dried seas left huge deposits of salt, which can be seen from the Coastal Plains up through the East Texas Basin.

 

Until the Mesozoic, not many changes took place in regard to plants for the next few hundred million years.  The prehistoric plants called Cycads became Cycadeoids during the Triassic and during the Jurassic the Caytonia developed.  Also, another major change happened to plants during the Jurassic.  A change that diversified the plant kingdom forever…angiosperms…flowering plants appeared.  Some groups of these plants evolved thousands of years ago and remain today virtually unchanged.  Other species reached their peak then died out before man existed.  Today there are two main groups left which are the gymnosperms and angiosperms.  At the same time, in the ocean, algae, which were possible ancestors of stromatolites, evolved and adapted to life there (Thomas, 23).

 

While water erosion worked its magic on the Cretaceous seas by distributing limestone, sandstone and mudstone into the Texas terrain, the Rocky Mountains were making their presence felt in West Texas, too.  As they heaved themselves upward, they pushed ancient Precambrian rocks up in the Franklin Mountains near El Paso through the Sierra Diablo near Van Horn.  Thus, the Balcones Fault became a release valve for pressure from deep inside the Earth. However, the last magnificent volcanic act was yet to play its part on Texas’ geological stage. During the Eocene and Oligocene epochs, these gigantic eruptions fulminated massive amounts of lave onto the West Texas terrain from Big Bend National Park, on through Alpine, to the Davis Mountains and into New Mexico’s borderline (Spearing, 19).

 

Today the landscape in Texas continues to change.  Erosional forces, such as wind and water, are Mother Nature’s carving tools.  Run-off water from the Rocky Mountain Range formed rivers that cut across the Panhandle of Texas draping the area with sand and gravel all the way to Fort Worth and Dallas.  Still the carving process continues.  Rivers of Texas such as the Red River, the Brazos, and the Colorado continue to erode the edge of the Panhandle High Plains area that originally was about 200 miles nearer to the Dallas-Fort Worth area. 

 

Additionally, one of the most obvious changes to the Dallas–Fort Worth area is practically in our back yards!  It took place where thousands of people congregate everyday...just as the dinosaurs did millions of years ago.  It is  the Dallas–Fort Worth International Airport!  Many kinds of dinosaurs prowled this area during the Mesozoic Era (Jacobs, 3).  Meanwhile, some of the dinosaurs’ relatives, such as the crocodiles and the birds, are still living in our present environments!  However, back then the majority of species were much different than those of today.  Equally important, from the Triassic through the Cretaceous, many kinds of dinosaur species evolved and became extinct while others continued to flourish until the late Cretaceous.  What happened to wipe away these magnificent animals?

 

This has been a hotly debated question for some time now.  However, there are many theories today. Scientists know that the late Cretaceous was marked by severe tectonic activity in the Pacific Basin.   Mountains were still being built and experiencing many changes during this time; these changes were not happening just in Texas but all over the world.  The ocean floor was spreading more rapidly than ever before in the Pacific.  The edges of the Pacific Basin became subduction zones that consumed the ocean’s crust.  As the crust was subducted under the continent, a string of volcanoes formed above the subduction zones.  One place where volcanic activity was particularly intense was in western and central India.  This activity was so pronounced that scientists gave it a name…the Deccan traps.  The lava flows from the eruptions were so extensive that many scientist believe that huge amounts of poisonous gases such as  sulfur oxides and perhaps nitric oxides, along with carbon dioxide, were interjected into the atmosphere which might have caused damage to the ozone layer and affected global temperatures and climates.  Still others hypothesize that increased volcanic eruptions may have contributed enough chemicals such as hydrochloric acid, nitric acid and sulfuric acid to cause acid rain which would have had a tremendous impact on vegetation (Fastovsky and Weishampel, 400).

 

 When investigating the extinction of dinosaurs, an equally important consideration was a change in climatic temperatures. Before the late Cretaceous, the trend in temperatures had been constant; however, towards the latter half of the Cretaceous, the average temperatures had dropped about five degrees from what they had been during the mid-Cretaceous time period.  This along with the changing positions of the continents contributed to the establishment of climates.  As a result, plants began to form recognizable Flora Zones (Thomas, 60).  Scientists speculate that the average temperature of dinosaur fauna was in a range of between 2 and 8 degrees centigrade during the late Cretaceous.  So perchance, due to climatic changes the dinosaurs’ menu had noticeably changed which perhaps did not include a diet they were formerly accustomed to eating (Fastovksy and Weishampel, 401).  Possibly these changes in climate caused many plants to die; that would wipe out the herbivores, and without herbivores, there would be no carnivores because carnivores rely on and plant eaters for their food.  Indeed, just a slight increase in temperature could have wiped out not only many plant species but two major classes of dinosaurs, as well.

 

            Another theory is the well-accepted asteroid impact.  In the 1970’s, Walter Alvarez a geologist at University of California at Berkeley was studying marine outcrops in Italy.  Alvarez knew that cosmic dust, a type of matter from outer space, constantly  falls on the Earth.  He felt that if he knew the rate at which this type of matter fell, he could calculate how much time had occurred during the deposition of a certain kind of rock (Fastovksy and Weishampel, 402).  However, to Alvarez’s amazement, he found an abrupt change in the rock that made up the shell beds of microscopic organisms in the late Cretaceous.  Upon closer inspection, he found that “these beds come to an end and next there follows[ed] a thin (2-3 cm) layer of clay, after which there abruptly begins the upper half of the exposure, made up almost exclusively of thin beds of the shells of microorganisms from the Tertiary Period. Obviously, there was a K/T boundary…” (Fastovksy and Weishampel, 402). Consequently, after studying the cosmic dust particles, Alvarez found that the particles contained the element iridium that is rarely found on Earth’s surface in high concentrations. However, the sample taken in Gubbio, Italy was thirty times higher than was usually found.  He presumed that the high concentration was a result of an asteroid impact that emitted a tremendous cloud of dust into the atmosphere that circled the globe. Perhaps this event contributed to blocking the sun’s rays (no photosynthesis), global warming (changes in climates), acid rain (damaged or killed plants), long term global cooling, or long term global warming (Fastovksy and Weishampel, 404).  All of these things could have had an enormous impact on the dinosaurs’ huge diet. 

 

So, you might ask, what does all this have to do with us today?   How does the extinction of the dinosaurs compare with what is happening to our world presently?  First, the dinosaurs extinction was mainly due to natural processes that occurred not to just the dinosaurs, but to other species such as plants that the dinosaurs depended on for life.  The prehistoric species had no control of their environment;  however, man does.  Most of the environmental threats to man have been of his own making.  Every second we are doing something that destroys factors that influence our environment.  The human species, like many others, influences and is influenced by his environment.  Human’s inventive nature has allowed them to live in the Arctic, the tropics, the mountains, and the deserts. We have changed our environments by building cities and roadways.  In fact, Earth has changed so much in the last 200 years that pioneers would be amazed at what man has accomplished in such a short time.  Conversely, although man has improved his standard of living, he has, due to poor conservation, destroyed deep, lush topsoil that took many years to develop (McLaren and Rotundo, 730).  Water habitats that were once homes for many species and sources of drinking water are struggling to survive.  Additionally, the air in many locations is constantly being monitored because it unhealthful to breathe. Likewise, the supply of fossil fuels that were made during the Carboniferous is being used at an alarming rate.

 

It has not been until recently that man has begun to realize the impact our species has on the Earth.  Today, the two main causes of pollution are created by actions of mankind. The first is high population density, which inhibits the ecosystem’s ability to rid itself of toxic substances.  The second cause is man’s materialism. As in all situations, there are trade offs; man has traded short term convinces for the very Earth that supports his life and the lives of future generations.

 

Today, we listen on the radio and television to see what the air pollution levels are because the air affects how we are able to breathe.  Likewise, many substances such as metals, paints, pesticides and other chemical vapors are being constantly emitted by industries into the atmosphere.  However, one of the major concerns associated with air pollution today is combustion or burning of substances which adds high concentrations of carbon dioxide to the atmosphere.  High carbon dioxide in the atmosphere is responsible for the greenhouse effect that is progressively causing temperature changes. Higher atmospheric temperatures could cause unusual circulation of air masses, causing violent storms such as tornadoes, hurricanes, and even El Ninos.  Further, higher temperatures could melt the polar ice caps creating a substantial rise in the ocean levels, causing flooding.

 

 Another ill-fated result of burning fossil fuels, such as coal with a high concentration of sulfur, is the emission of sulfur dioxide into the air.  When sulfur dioxide joins with water particles in the air, acid rain is produced.  Acid rain can kill plants and change the pH of the soil; it can kill fish and inhibit some bacteria’s ability to fix nitrogen; it can damage structural surfaces such as brick, stone, and metals…not to mention what it might be doing to our skins! Equally important, when temperatures rise or drop from a certain range, organisms began having difficulty with their metabolic processes.  Global temperature is closely related to organisms’ metabolic rates.  At 0 degrees centigrade, metabolism becomes insufficient in most organisms.  If the temperature is too hot, or is above 50 degrees centigrade, then enzymes began to denature (Campbell,1003). Therefore, their surrounding temperature environments affect most organisms.  If the temperature changes more than a few degrees above or below the accustomed temperature, the organism cannot maintain its body temperature and will die.  Therefore, controlling global warming is important to all life on earth.

 

Another abiotic factor that influences our environment is water.  Everything must have clean water.  In the U.S., Americans use and waste many gallons of clean water each day. Aquifers such as the Edwards Aquifer in the San Marcus area in Texas produces billions of gallons of water every day; yet this is not enough. Likewise, fertilizers, pesticides, salt from icy freeways, sediment from erosion, and large amounts of treated sewage are released into our water systems. Rubber particles from tires being worn down by the roads we drive upon each day and oil from leaky engines run off the roads into our water systems when it rains.  Also, polluted water could affect sea kelp’s ability to absorb light, which would impede photosynthesis resulting lower oxygen production for the atmosphere. With all this floating around in our water supplies, how can water plants and animals survive?   If water dies so do plants and so do we!

 

Additionally, the pH and mineral composition present in the soil affect the distribution of plants, and the animals that consume these plants.  Acid rain, mineral mining, and fertilizers could affect the pH and the mineral composition of the soil; thus limiting the amount of food crops that could be grown, lumber production, and plants that provide fibers for fabrics for consumer use.

 

Fires and volcanic eruptions consume forests, destroy habitats, pollute the air and cut down on the amount of plants available to produce oxygen for other organisms to consume.  Many times carelessness on man’s part can destroy acres and acres of forest that took years to grow. An example is the fires in New Mexico in June of 2000 that destroyed thousands of acres of forestlands and homes.

 

Today, concerned groups such as EPA have established regulations in industrialized nations to protect the fragile homeostasis of our planet. Unfortunately, other newly industrialized nations ignore the warnings of environmentalists. In spite of their efforts, ignorant and self-serving individuals continue to destroy the Rain Forest at an alarming rate.  As I write, species’ habitats are being destroyed which most likely will lead to their extinction.  Some of these organisms may possess the potential to cure serious illnesses such as various cancers, HIV, and some kinds of birth defects to name a few; yet, we may never have the opportunity to discover their medicinal qualities.

 

            Nevertheless, possibly the most dangerous pollutant of all is mankind.  Although we have devised many ways to prevent pollution such as sewage waste plants, automobile emissions control, conservation and many others, man could indeed be his worst enemy.  Overpopulation is putting too much pressure on a planet that is already over burdened to produce food; clothing; clean water and air; shelter, and all of the other material possessions we all hold so dear to our hearts. All of these factors and too many others to mention are leading to the extinction of the human race. If mankind continues in the same vein, he can expect to last approximately only 200 more years according to Dr. Fred Fifer at UTD. However, unlike the poor dinosaurs we do have a choice.  What will your choice be…  life or extinction for future generations?

 

Works Sited

 

            Cambell, Neil A..  Biology. The Benjamin/Cummings Publishing Company, Menlo Park, California, 1987.

 

Fastovsky, David E. and Weishampel, David B.. The Evolution and Extinction of the Dinosaurs.  Cambridge University Press, U.S.A., 1996.

 

            Jacobs, Lewis. Cretaceous Airport: The Surprising Story of Real Dinosaurs at D.F.W.. The Saurus Institute, 1993.

 

Johnson, Kirk R. and Stucky, Richard K..  A History of Life On Earth.  Roberts Rhinehart Publishers, Colorado, 1995.

 

Sheldon, Robert A.  Roadside Geology of Texas, Second edition.  Mountain Press Publishing Company, Montana, 1979.

 

Spearing, Darwin.  Roadside Geology of Texas. Sixth printing.  Mountain Press Publishing Company, Missoula, Montana, 1991.

 

Thomas, Barry.  The Evolution of Plants and Flowers.  St. Martin’s Press, New York, 1981.

 

Copyright © 2000, UTD Science Education. All rights reserved.

 

 

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and was produced for the GLOBAL ENVIRONMENTAL CHANGE program funded by a grant from the National Science Foundation and the Woodrow Wilson National Fellowship Foundation; sponsored by the University of Texas at Dallas - Science Education Department with support from Duncanville Independent School District.