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The Purple Earth Hypothesis (PEH) is an astrobiological hypothesis, first proposed by molecular biologist Shiladitya DasSarma in 2007, [1] that the earliest photosynthetic life forms of Early Earth were based on the simpler molecule retinal rather than the more complex porphyrin-based chlorophyll, making the surface biosphere appear purplish ...
The timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history. Each object is listed in chronological order of its discovery (multiple dates occur when the moments of imaging, observation, and publication differ), identified through its various designations (including temporary and permanent schemes), and the ...
Rare Earth was succeeded in 2003 by the follow-on book The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of our World, also by Ward and Brownlee, which talks about the Earth's long-term future and eventual demise under a warming and expanding Sun, showing readers the concept that planets like Earth ...
In Chevreul's 1839 book The principles of harmony and contrast of colours, [12] he introduced the law of color contrast, stating that colors that appear together (spatially or temporally) will be altered as if mixed with the complementary color of the other color, functionally boosting the color contrast between them. For example, a piece of ...
Pale Blue Dot is a photograph of Earth taken on February 14, 1990, by the Voyager 1 space probe from an unprecedented distance of over 6 billion kilometers (3.7 billion miles, 40.5 AU), as part of that day's Family Portrait series of images of the Solar System.
Another example is Earth's axial tilt, which, due to friction raised within Earth's mantle by tidal interactions with the Moon , is incomputable from some point between 1.5 and 4.5 billion years from now. [104] The outer planets' orbits are chaotic over longer timescales, with a Lyapunov time in the range of 2–230 million years. [105]
Early photos of Earth taken from space inspired a mild version of the overview effect in earthbound non-astronauts, and became prominent symbols of environmental concern. [ 1 ] English astronomer Fred Hoyle wrote in 1948 that, "once a photograph of the Earth, taken from the outside, is available, a new idea as powerful as any in history will be ...
Isaac Newton suggests the existence of an aether in the Third Book of Opticks (1st ed. 1704; 2nd ed. 1718): "Doth not this aethereal medium in passing out of water, glass, crystal, and other compact and dense bodies in empty spaces, grow denser and denser by degrees, and by that means refract the rays of light not in a point, but by bending them gradually in curve lines? ...