What are the three major mechanisms of evolution differ in how they work

Evolution is the process through which the different organisms advances from having less developed form or the position into a less-perfect form. As, different species go through different pathways in which they attain a new and complex form of mechanism to survive inside a region or given parameters.While, the process of evolution takes place in a three main different forms or ways, or briefly in three different pathways:The natural selection: Species goes through different process in which they deal with the number of obstacles, like the limitation of food resources, having the competition for the shelter and resources etc. During, such a process the species either goes into extinction or they survive for a much longer time then expected.The Genetic flow: The species have a given set of genes or more over genome which they posses for having a specific identity among the diverse form of organisms.The different species may go through the mutations or even may go through the different form of gene losses. As, due to the changes inside the overall environment or the system of the organisms the difference or diversity inside the genome of the organisms may occur.  The Genetic drift:  The genetic drift is the displacement which causes the changes inside the different species over all existence. For example, lets genetic drift may be termed as the process which is brought by a set of species which are detached from its over all population and it brings change along with variety by introduction of that small population inside the given region.                                                                                                                                                                                                                      

Very hard to understand

Environmental science studies the interactions between the physical, chemical, and biological components of the environment, including their effects on all types of organisms. earth science (also known as geoscience), is an inclusive term for all sciences related to earth (geology, meteorology, oceanogr maphy, etc).  although environmental and earth science cover essentially the same material, environmental science places greater emphasis on the biological realm, while earth science places greater emphasis on the physical realm.    environmental and earth science study the interactions of four major systems or “spheres” (figure 8.6).  the  geosphere  consists of the core, mantle and crust of the earth.the  atmosphere  contains all of the earth’s air and is divided into troposphere, stratosphere, mesosphere, thermosphere and ionosphere.the  hydrosphere  contains all of the solid, liquid and gaseous water on earth, extending from the depths of the sea to the upper reaches of the troposphere where water is found.  ninety-seven percent of the hydrosphere is found in salty oceans, and the remainder is found as vapor or droplets in the atmosphere and as liquid in ground water, lakes, rivers, glaciers and snowfields.  the  biosphere  is the collection of all earth’s life forms, distributed in major life zones known as biomes:   tundra, boreal forest, temperate deciduous forest, temperate grassland, desert, savannah, tropical rainforest, chaparral, freshwater, and marine.although the four systems have their unique identities, there is substantial interaction between them.  environmental scientists study the effects of events in one sphere on the other spheres. for example, a volcanic eruption in the geosphere may cause profound direct and indirect effects on the hydrosphere, atmosphere and biosphere as follows: example 1 (volcano)    on may 18, 1980, mount saint helens, in the state of washington, erupted.  this event altered the surrounding environment, and provided scientists with an opportunity to study the effects of volcanic eruptions on the geosphere, hydrosphere, atmosphere and biosphere.  such studies are vital because volcanic eruptions will continue to occur, and will have increasing impact on humans as people continue to settle lands closer to dormant volcanoes. the following are but a few of the myriad of interactions resulting from a volcanic