At this time, the oxygen level was approximately 10% of its present atmospheric concentration. The amount of ozone required to shield Earth from biologically lethal UV radiation, wavelengths from 200 to 300 nanometers (nm), is believed to have been in existence 600 million years ago. The thin layer of ozone that surrounds Earth acts as a shield, protecting the planet from irradiation by UV light. High in the atmosphere, some oxygen (O 2) molecules absorbed energy from the Sun's ultraviolet (UV) rays and split to form single oxygen atoms, which combined with remaining oxygen (O 2) to form ozone (O 3) molecules that are very effective at absorbing UV rays. As oxygen in the atmosphere increased, CO 2 decreased. Some of the photosynthetically created oxygen combined with organic carbon to recreate CO 2 molecules the remaining oxygen accumulated in the atmosphere. This solar energy conversion process is known as photosynthesis. One billion years ago, early aquatic organisms called blue-green algae began using energy from the Sun to split molecules of H 2O and CO 2, and recombine them into organic compounds and molecular oxygen (O 2). Elements in this state are not found in the rocks of mid-Precambrian and younger ages, less than 3 billion years old. Evidence of such an anaerobic reducing atmosphere is hidden in early rock formations that contain many elements, such as iron and uranium, in their reduced states.
#The four elements free
The most important feature of the ancient environment was the absence of free oxygen. The hydrosphere was formed 4 billion years ago from the condensation of water vapor, resulting in oceans of water in which sedimentation occurred. Prior to 3.5 billion years ago, the atmosphere probably consisted of carbon dioxide (CO 2), carbon monoxide (CO), water (H 2O), nitrogen (N 2), and hydrogen (H). These gases may have consisted of hydrogen (H 2), water vapor, methane (CH 4), and carbon oxides. In the first 500 million years of Earth's history, a dense atmosphere emerged from the vapor and gases that were expelled during degassing of the planet's interior. 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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