How Was the World Formed?
In the beginning our universe was a mass of white-hot vapors and molten materials whirling about in space. Our world was formed from this. Astronomers believe it took millions of years for the cloud to cool, contract and begin to turn into molten rock.
Modern astronomers think that many millions of years ago there was a huge explosion in space. They do not know exactly what happened. But it is possible that our sun exploded or that a much bigger companion star of the sun became a supernova—that is, it broke up violently. The debris and blazing gases from this explosion were, it is thought, flung far into space.
For more millions of years our solar system boiled and bubbled. But very slowly, the fiery redness began to cool and condense into the nine planets and many smaller bodies. All these planets now revolve around the sun. After further vast periods of time the lava of the earth began to solidify, developing over many millions of years, into the world as we know it today.
The world is the planet Earth and all life upon it, including human civilization. In a philosophical context, the world is the whole of the physical Universe, or an ontological world. In a theological context, the world is the material or the profane sphere, as opposed to the celestial, spiritual, transcendent or sacred. The “end of the world” refers to scenarios of the final end of human history, often in religious contexts.
History of the world is commonly understood as spanning the major geopolitical developments of about five millennia, from the first civilizations to the present. In terms such as world religion, world language, world government, and world war, world suggests international or intercontinental scope without necessarily implying participation of the entire world.
World population is the sum of all human populations at any time; similarly, world economy is the sum of the economies of all societies or countries, especially in the context of globalization. Terms like world championship, gross world product, world flags imply the sum or combination of all current-day sovereign states.
The history of Earth concerns the development of Planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to the understanding of the main events of Earth’s past. The age of Earth is approximately one-third of the age of the universe. An immense amount of geological change has occurred in that timespan, accompanied by the emergence of life and its subsequent evolution.
Earth formed around 4.54 billion years ago by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere and then the ocean; but the atmosphere contained almost no oxygen and so would have been toxic to most modern life including humans. Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism.
A giant impact collision with a planet-sized body named Theia while Earth was in its earliest stage, also known as Early Earth, is thought to have been responsible for forming the Moon. Over time, the Earth cooled, causing the formation of a solid crust, and allowing liquid water to exist on the surface.
The geological time scale (GTS) clock depicts the larger spans of time from the beginning of the Earth as well as a chronology of some definitive events of Earth history. The Hadean Eon represents time before the reliable (fossil) record of life beginning on Earth; it began with the formation of the planet and ended at 4.0 billion years ago as defined by international convention.
The Archean and Proterozoic eons follow; they produced the abiogenesis of life on Earth and then the evolution of early life. The succeeding eon is the Phanerozoic, which is represented by its three component eras: the Palaeozoic; the Mesozoic, which spanned the rise, reign, and climactic extinction of the huge dinosaurs; and the Cenozoic, which presented the subsequent development of dominant mammals on Earth.
Hominins, the earliest direct ancestors of the human clade, rose sometime during the latter part of the Miocene epoch; the precise time marking the first hominins is broadly debated over a current range of 13 to 4 mya. The succeeding Quaternary period is the time of recognizable humans, i.e., the genus Homo, but that period’s two million-year-plus term of the recent times is too small to be visible at the scale of the GTS graphic.
The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago, during the Eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. There are microbial mat fossils such as stromatolites found in 3.48 billion-year-old sandstone discovered in Western Australia.
Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Greenland as well as “remains of biotic life” found in 4.1 billion-year-old rocks in Western Australia. According to one of the researchers, “If life arose relatively quickly on Earth … then it could be common in the universe.”
Living forms derived from photosynthesis appeared between 3.2 and 2.4 billion years ago and began enriching the atmosphere with oxygen. Life remained mostly small and microscopic until about 580 million years ago, when complex multicellular life arose, developed over time, and culminated in the Cambrian Explosion about 541 million years ago. This event drove a rapid diversification of life forms on Earth that produced most of the major phyla known today; and it marked the end of the Proterozoic Eon and the beginning of the Cambrian Period of the Paleozoic Era.
More than 99 percent of all species, amounting to over five billion species that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth’s current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described.
Geological change has been a constant of Earth’s crust since the time of its formation, and biological change since the first appearance of life. Species continue to evolve, taking on new forms, splitting into daughter species or going extinct in the process of adapting or dying in response to ever-changing physical environments.
The process of plate tectonics continues to play a dominant role in the shaping of Earth’s oceans and continents and the living species they harbor. Changes in the biosphere—now dominated by human activity—continue, in turn, to produce significant effects on the atmosphere and other systems of the Earth’s surface, such as the integrity of the ozone layer, the proliferation of greenhouse gases, the conditions of productive soils and clean air and water, and others.