Losing Biodiversity—chapter 1:
Biodiversity is the sum total of life forms
This diversity of organisms, or species, includes bacteria and viruses, as well as dandelions, mushrooms, and mosquitoes. The endangered habitats that support life range from tide pools and deserts to peat bogs and unexplored rain forests. Human cultures are also an important part of Earth’s biodiversity.
Biologists estimate that there are between 7 million and 15 million different kinds of organisms alive on Earth today. The wide difference in the estimates is because scientists know so little about what lives in remote areas. Only 1,700,000 (1.7 million) living species have been studied. In your school yard or in the vacant lot down the street, there may be living things that no one has ever taken the time to study or name.
This book presents scientific processes and knowledge to help you identify causes of species extinction and habitat loss as well as potential solutions. As you learn about evolution, natural selection, genetics, and ecosystems, you will gain information and tools for conserving natural resources. In each chapter, you will encounter the work of scientists who have made important contributions to understanding life on our planet. The book also presents the successful efforts of citizens to reduce the impact of human society on the natural world. These efforts are paving the way for achieving a sustainable global economy that maintains the productivity of Earth’s ecosystems.
In ancient sedimentary rocks of Western Australia, scientists have found fossils that were formed by clusters of bacteria growing in coastal tide pools 3,500,000,000 (3.5 billion) years ago. Little is known about the structure of these early life forms other than they resemble modern bacteria. Another 3 billion years passed before more complex marine organisms, such as jellyfish and worm-like creatures, became common in the fossil record. It is still a mystery how the first bacteria evolved into the more complex organisms, because their small soft bodies left few clues behind in the layers of sediments.
Examine the following graph that summarizes the research of paleontologists (scientists who study fossil life). You can see that over time, the different kinds of marine organisms identified in the fossil record have increased. There are deep valleys where the kinds of fossils are greatly reduced.
Find the time period when more than 80% of ocean organisms became extinct. Scientists haven’t yet discovered what caused this greatest of all known extinctions that occurred 240,000,000 (240 million) years ago. Another gigantic extinction occurred 65,000,000 (65 million) years ago, killing most marine organisms and wiping out the dinosaurs. (Reprinted with permission of the author from Dr. Art's Guide To Planet Earth, by Art Sussman.)
The causes of the mass extinctions are still under study and debate. Various hypotheses have included: climate change, such as periods of cooling and warming; changing composition of the atmosphere and ocean; continental drift; impacts of asteroids; and emergence of aggressive new species. Paleontologists have discovered that new kinds of species emerged following each great extinction, so that the trend over millions of years has been an increase in the overall biodiversity of the planet.
Near the end of the Pleistocene ice age, 40,000 years ago, human populations expanded into Europe, Northern Asia, North America, and Australia. Paleontologist, Paul Martin and colleagues, have pieced together evidence that the decrease in megafauna species (large animals) followed the migration of human hunters into new regions. In their article, “Prehistoric Overkill: the Global Model” they provide compelling data for the link between early hunting cultures and the loss of large species. This is the first mass extinction that can be linked to the actions of humans.
Within a few thousand years, North America lost more than 70% of all large mammals, including species of horses, camels, giant sloths, giant armadillos, saber tooth cats, dire wolves, lions, mammoths and mastodons. Their remains have been identified among the tools and objects of early human settlements. As human populations expanded into Central and South America, 80% of large animals became extinct. The extinction pattern in Europe and Asia was much the same. Cave paintings in southern Europe document the hunting activities that exterminated animals like the giant cave bear.
The impact of early humans on Australian species was even greater with the extinction of 86% all marsupial mammals, including several giant kangaroos, marsupials resembling the rhinoceros, tapirs, ground sloths, and a giant lizard. As human populations spread through the oceanic islands, more than 1,000 species of island birds became extinct, many of them large flightless species.
While extinctions have occurred frequently throughout Earth’s history, there is no evidence that any species prior to our own has caused a mass extinction similar to the one that is currently underway. Our modern impacts greatly exceed the prehistoric activities of our ancestors in several dramatic ways:
How do we know that loss of biodiversity can cause problems for people and the planet? In the chapters ahead, reports of scientific studies provide evidence of global problems and strategies for reducing our impact on the environment.
On a brighter note, people can learn from history and science and take action to decrease their negative impacts on the biosphere. The following activity, Assessing Biodiversity, will give you experience using research methods that can guide biodiversity restoration efforts.
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