HOW DOES LIFE BEGINS
In three and a half billion years, life on earth has transformed from single cells to complex multicellular organisms. Life permeates all environments on Earth and is a defining characteristic of our planet. It occurs in the biosphere, a thin layer between the upper part of Earth's troposphere and the topmost layers of porous rocks and sediments. The size and nature of the biosphere has grown and changed over time, as has the relationship between organic and in organic elements in the biosphere.
HISTORY
In the beginning, the conditions on Earths were limiting, and the first cells formed from molecular buildings blocks reflected this. Early organisms were single-celled prokaryotes, such as bacteria, that lacked a defined nucleus. A billion and a half years later, eukaryotes, such as amoebas, appeared: singled - celled organisms that possess a bounded nucleus and rely on oxygen to function. These two categories of cells have persisted through time in an unbroken sequence, while also evolving into the myriad and astonishingly diversified life forms found on the planet today.
Humans should not be viewed as the culmination of life on the Earth. like all situations involving natural selection, the pathway that led to Homo sapiens was not predetermined, but variable. A sequence of many favorable circumstances was necessary for the human species to evolve. Had not a cataclysmic event occurred some 65 million years ago, dinosaurs still might be the dominant vertebrates on the planet, as they had been for the 100 million years during which they coexisted with early mammals. If one group of organisms is to be singled out for its longevity and adaptability, it is bacteria . Bacteria have been hare since the beginning and in all likelihood will be here at the end.
WHAT IS PHOTOSYNTHESIS
Photosynthesis is a life process powered by the sun. Directly or indirectly through the food chain, it fuels most life on Earth. Photosynthesis is carried out by green plants and some types of algae as well as by cyanobacteria (formerly known as blue green algae) and related organisms, which are responsible for most of the photosynthesis in oceans.
In the process of photosynthesis, plants capture sunlight and absorb carbon di oxide from the atmosphere. The light and Carbon di oxide combine with water, brought in by plant roots. The end product is sugars, food for the plant; a waste product is oxygen , respired out through the plant leaves.
Thus plants use carbon di oxide that animals breathe out and provide oxygen that animals breathe in. Photosynthesis provides all the food we eat-plants and animals that eat plants- and the oxygen we breathe. If photosynthesis were to cease, the atmosphere's oxygen would likely be depleted within several thousand years. Photosynthesis also created the raw materials for the fossil fuels we so depend on. Green plants formed the bulk of the organic deposits that through geological processes were transformed into coal, oil, and natural gas.
FAST FACTS
Half of all oxygen comes from photosynthesizing, one-celled plants on the ocean surface.
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