The age of the Earth has been determined to be about 4.5 billion years (4,540,000,000 years),[1] corresponding approximately to one third of the age of the universe, and immense geological and biological changes and upheavals have occurred during that time span. The formation of the Earth and the simultaneous formation of the Sun and other bodies of the solar system resulted from the contraction of a solar nebula. The nebula developed into a protoplanetary disk with the Sun forming in its centre and the planets forming by accretion of material in orbit around it. The Earth was formed 10 million years after the beginning of contraction. Heat generated by impacts and contraction meant that it was totally molten, and a differentation took place, forming an inner core of the heaviest elements and a mantle and proto-crust of the lighter elements. Around this time the Moon was formed, possibly by a giant impact between the Earth and a smaller planet. The Earth was steadily cooling and acquired a solid crust that gave rise to the first continents. A major bombardment from icy meteorites and comets supplied the Earth with an enormous amount of water that created the oceans, while volcanic activity and water vapor created an atmosphere, devoid of oxygen. The continents floated on the molten mantle of the planet and through plate tectonics assembled into supercontinents that later broke up again in a process that has been repeated several times during the passing of the billions of years.
Chemical reactions created organic molecules which interacted to create still more elaborate and complicated structures, and finally gave rise to a molecule that was able to create copies of itself. This abilitiy initiated the evolution and led to the creation of life. At first life started in the form of one-celled organisms but later multicellularity developed, and a major evolution was the process of photosynthesis which supplied oxygen to the atmosphere and led to the creation of an ozone layer. The life forms branched into many species and became still more advanced, colonizing the land and gradually filling all the habitats of the Earth. Ice ages, volcanic eruptions, and major impacts of meteorites have caused several mass extinctions of life forms, but the remaining species have developed in new directions and have created a lasting biosphere.
About six million years ago, a split of branches of what was then the evolutionary family tree ultimately led to the modern man. The ability to walk upright, an increase in brain size, and improvement of communication skills were crucial factors. Man learned to control fire, developed agriculture and began systematic husbandry of animals and plants. This improved living conditions and societies and civilizations with religious and cultural characteristics formed. Through progress in science, writing, organization of governments, transportation and communication, man has become the dominant species on Earth and influences the environment and all other life forms. The scope of human activity and an increasing population now require mankind to apply a global perspective on major concerns and problems like protection of the environment, exploitation of natural resources, protection of wildlife, and climate change.
Chemical reactions created organic molecules which interacted to create still more elaborate and complicated structures, and finally gave rise to a molecule that was able to create copies of itself. This abilitiy initiated the evolution and led to the creation of life. At first life started in the form of one-celled organisms but later multicellularity developed, and a major evolution was the process of photosynthesis which supplied oxygen to the atmosphere and led to the creation of an ozone layer. The life forms branched into many species and became still more advanced, colonizing the land and gradually filling all the habitats of the Earth. Ice ages, volcanic eruptions, and major impacts of meteorites have caused several mass extinctions of life forms, but the remaining species have developed in new directions and have created a lasting biosphere.
About six million years ago, a split of branches of what was then the evolutionary family tree ultimately led to the modern man. The ability to walk upright, an increase in brain size, and improvement of communication skills were crucial factors. Man learned to control fire, developed agriculture and began systematic husbandry of animals and plants. This improved living conditions and societies and civilizations with religious and cultural characteristics formed. Through progress in science, writing, organization of governments, transportation and communication, man has become the dominant species on Earth and influences the environment and all other life forms. The scope of human activity and an increasing population now require mankind to apply a global perspective on major concerns and problems like protection of the environment, exploitation of natural resources, protection of wildlife, and climate change.
