The correct answer is - cyanobacteria.
The atmospheric oxygen came from the cyanobacteria. These were one of the earliest living organisms on Earth. The cyanobacteria was using photosynthesis in order to create its own food. The photosynthesis process requires sunlight, carbon dioxide, water, and oxygen. The oxygen is mostly released as a waste product from the process of photosynthesis, thus the cyanobacteria were literally releasing oxygen that was ending up into the atmosphere. As more and more cyanobacteria there were across the planet, more and more oxygen they were releasing into the atmosphere, slowly changing the composition of the atmosphere, and setting the basis of it as we know it now.
The country that is an isthmus and links central and Souh America is Panama
<span>The topography of the Midwest is relatively flat</span><span>
Topography is the shape or configuration of the land, its physical features represented on a map by contour lines, hypsometric tints, and relief shading.
Hope this helped.</span>
Answer:
Humans alter their environment in many ways. We burn fossil fuels to produce electricity and to power cars, airplanes, and much more. We also remove land to build businesses, homes, and stores, and to grow food. We cut down forests to make things like paper, desks, and houses, and we hunt or raise animals for food. And lastly, we divert rivers to store water in reservoirs and to irrigate farmland.
