Evolution
An area of the Amazon Rainforest shared betweenColombia and Brazil. The tropical
rainforests of South America contain the largest diversity of species onEarth
Main article: Evolution
.jpg)
Life is only
known to exist on the planet Earth.(cf Astrobiology) The origin of life is still a poorly understood process, but it is thought to have occurred
about 3.9 to 3.5 billion years ago during the hadean or archean eons on a primordial earth that
had a substantially different environment than is found at present.[58] These life forms possessed the
basic traits of self-replication and inheritable traits. Once life had
appeared, the process of evolution by natural selection resulted in the development of ever-more diverse life forms.
Species that
were unable to adapt to the changing environment and competition from other
life forms became extinct. However, the fossil record retains evidence of many
of these older species. Current fossil and DNA evidence shows that all existing
species can trace a continual ancestry back to the first primitive life forms
.jpg)
The advent of photosynthesis in very basic forms of plant life worldwide allowed the sun's energy to
be harvested to create conditions allowing for more complex life.[citation
needed] The resultant oxygen accumulated in the atmosphere and
gave rise to the ozone layer. The incorporation of smaller cells within larger ones resulted in the development
of yet more complex cells called eukaryotes.[59] Cells within colonies became
increasingly specialized, resulting in true multicellular organisms. With the ozone layer
absorbing harmful ultra
plants and animals
.jpg)
Main articles: Plant and Animal: Originally Aristotle divided all living things between plants, which generally do not move
fast enough for humans to notice, and animals. In Linnaeus' system, these became the kingdoms Vegetabilia (laterPlantae) and Animalia. Since then, it has become clear that the Plantae as originally defined
included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these are still often considered
plants in many contexts. Bacterial life is sometimes included in flora,[64][65] and some classifications use the term bacterial
floraseparately from plant
flora.
Among the many
ways of classifying plants are by regional floras, which, depending on the purpose of study, can also include fossil flora, remnants
of plant life from a previous era. People in many regions and countries take great pride in their individual arrays of characteristic flora, which can vary widely across the globe due to differences in climate and terrain.
of plant life from a previous era. People in many regions and countries take great pride in their individual arrays of characteristic flora, which can vary widely across the globe due to differences in climate and terrain.
Regional
floras commonly are divided into categories such as native flora and agricultural
and garden flora, the lastly mentioned of which are intentionally grown and
cultivated. Some types of "native flora" actually have been
introduced centuries ago by people migrating from one region or continent to
another, and become an integral part of the native, or natural flora of the
place to which they were introduced. This is an example of how human
interaction with nature can blur the boundary of what is considered nature.
.jpg)
Another
category of plant has historically been carved out for weeds. Though the term has
fallen into disfavor among botanists as a formal way to categorize
"useless" plants, the informal use of the word "weeds" to
describe those plants that are deemed worthy of elimination is illustrative of
the general tendency of people and societies to seek to alter or shape the
course of nature. Similarly, animals are often categorized in ways such as domestic,farm animals, wild animals, pests, etc. according to their
relationship to human life.
Animals as a category have several characteristics that generally set them apart
from other living things. Animals are eukaryotic and usually multicellular (although see Myxozoa), which separates
them from bacteria, archaea and most protists. They are heterotrophic, generally digesting food in an internal chamber, which separates them
from plants andalgae. They are also
distinguished from plants, algae, and fungi by lacking cell walls.
With a few
exceptions, most notably the sponges (Phylum Porifera), animals have bodies differentiated into separate tissues.[citation
needed] These include muscles, which are able to
contract and control locomotion, and a nervous system, which sends and processes signals. There is also typically an internal digestive chamber. The eukaryotic cells
possessed by all animals are surrounded by a characteristic extracellular
matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures likeshells, bones, and spicules, a framework upon which
cells can move about and be reorganized during development and maturation, and
which supports the complex anatomy required for mobility.
.jpg)
Human interrelationship
Despite their natural beauty, the secluded valleys
along the Na Pali Coast in Hawaii are
heavily modified by introduced invasive species such as She-oak
Although
humans currently comprise only a minuscule proportion of the total living
biomass on Earth, the human effect on nature is disproportionately large.
Because of the extent of human influence, the boundaries between what humans
regard as nature and "made environments" is not clear cut except at
the extremes. Even at the extremes, the amount of natural environment that is
free of discernible human influence is presently diminishing at an increasingly
rapid pace.
The
development of technology by the human race has allowed the greater
exploitation of natural resources and has helped to alleviate some of the risk
from natural hazards. In spite of this progress, however, the fate of human civilization remains closely linked to changes in the environment. There exists a
highly complex feedback loop between the use of advanced technology and changes
to the environment that are only slowly becoming understood. Man-made threats to the Earth's
natural environment include pollution,deforestation, and disasters such as oil spills. Humans have contributed to the extinction of many plants and animals.
.jpg)
Humans employ
nature for both leisure and economic activities. The acquisition of natural
resources for industrial use remains the primary component of the world's
economic system.[citation
needed] Some activities, such as hunting and fishing, are used for both sustenance and leisure, often by different people. Agriculture was first adopted around the 9th
millennium BCE. Ranging from food
production to energy, nature influences
economic wealth.
Although early
humans gathered uncultivated plant materials for food and employed the
medicinal properties of vegetation for healing,[67]most modern human use
of plants is through agriculture. The clearance of large tracts of land for
crop growth has led to a significant reduction in the amount available of
forestation and wetlands, resulting in the loss of habitat for many plant and
animal species as well as increased erosion.
.jpg)
.jpg)
.jpg)