LIFE BEGINS
In three and the half billion years, life on earth has transformed from single celles to complex multicellular organisms. Life permeates all environments on earth and is a defining characteristica of our plant. 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 the nature of the biosphere has grown and changed over time, as has the relationship between organic and inorganic elements in the biosphere.
In the beginning, the condition on Earth were limiting, and the first cells formed from molecular building 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 amobas, appeared: single-celled organisms thay 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-fprms found on the planet today.
Humans should not be viewed as the culmination of life on earth . Like all situations involving natural selection, the pathway that led to Homo sapiens (scientific name of human) was not lredetermined ,but variable. A sequence of many favorable circumstances was necessary for the human species to envolve. Had not a cataclysmic event occurred slme 65 million years ago , dinosaurs still might be the dominant verte rates on the planet, as they had been for the 100 million years during which they coexisted with early mammales. If is bactaria. Bacteria have been here since the beginning and in all likelihood will be here at the end.
EUKARYOTE: From Greek eu-,good, + karyon, nut or kernel. Any organis. Composed of one or more cells, each of which contains a clearly defined nucleus enclosed by a menbrane, alongvwith organelles – small, self -contained, clular parts that perform specific function. PROKARYOTE: From Greek pro-, before, + karyon, nut or kernel. Any cellular organism that lacks a distanct nucleus.
