Many researchers think that, instead of water forming at the same time as Earth, objects in the outer solar system delivered water to Earth in violent collisions shortly after its formation. The exact origin of our planet's water, which covers about 70% of Earth's surface, is still a mystery to scientists. While the eons that followed were full of strange stories and far-reaching changes, the Earth had taken on its basic structure long before. The oldest rocks, dated by the uranium-lead method at about 3.96 billion years old, show that there were volcanoes, continents, oceans, crustal plates, and life on Earth in those days. Since this theory took center stage in the mid-1980s, it has become everyone's favorite, as geophysicist Don Anderson once explained, “The objection that such an event would be extremely rare is actually a point in its favor, since the Moon is unique”. The planet got most of it back after a period of time, but some of it collected into a second mini-planet circling Earth, the Moon. The chunks, boulders, and mini-planets left behind continued to collect into large, stable bodies in well-spaced orbits.Īt one point early in this process a very large mini-planet struck Earth an off-center blow, spraying much of Earth's rocky mantle into space. Materials, which we can call rocks and iron metal, began to sort themselves out the dense iron settled in the center, while lighter rock separated into a mantle around it, in a miniature of Earth and the other inner planets today.Īt some point, the Sun ignited although the Sun was only about two-thirds as bright as it is today, the process of ignition was energetic enough to blow away most of the gaseous part of the protoplanetary disk. Slowly, these grains settled together into clusters, then lumps, then boulders, and finally bodies large enough to exert their own gravity.Īs time went by, these bodies grew by collision with other bodies, producing a lot of melting and vaporization. Iron metal and compounds of silicon, magnesium, aluminum, and oxygen came out first in that fiery setting bits of these are preserved in chondrite meteorites *. This took millions of years, during which the components of the disk began to freeze out into small dust-size grains. While the Sun grew in size and energy, the hot disk slowly cooled. The new star became our Sun, and the glowing disk gave rise to Earth and its sister planets. The mixture grew hot and compressed under its own gravity at its center, a new star began to form, around which swirled a disk of the same material that grew white-hot from the great compressive forces. Some 5 billion years ago, a supernova exploded, pushing a lot of its heavy-element wreckage into a cloud of hydrogen gas and interstellar dust. Generations of stars were born in gas clouds and died in explosive novas that produced the heavier elements we have today. Ten billion years before the Earth was born, the universe started out with only two elements: hydrogen and helium, which formed stars that burned these elements in nuclear fusion reactions. Fire meant the Sun and flame it also indicated creative passion and destructive zeal.īefore digging into the myriad of aspects of how the Four Elements in fact shape and affect our life, this is the back-story of how they originated. Air was not only the air we breathe and the atmosphere, but signified the mind, intelligence, and inspiration. Water, flowing and ever-changing, denoted emotion and empathy. For instance, the Earth, solid and substantial, was associated with the physical and sensual aspects of life. To the ancient Greeks, the four elements described not only physical manifestations of the material world but essential qualities of human nature as well. This is similar to what really happens with elements and all molecules at an atomic level. Although the Greeks believed that the four elements were unchanging in nature, everything was made up of these elements, held together or pushed apart by forces of attraction and repulsion, causing substances to appear to change. Historians believe that as early as the 8 th century BCE, ancient Greek philosophers of the Archaic period began formulating theories of the four classical elements. The idea that these four elements-Earth, Water, Air, and Fire-made up all matter was the cornerstone of philosophy, science, and medicine for two-thousand years. From ancient civilizations to modern day, the colors and symbols of the four elements have represented the different aspects of nature and the forces of energy in our world.
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