Search results
Results from the WOW.Com Content Network
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 earliest evidence for life on Earth includes: 3.8 billion-year-old biogenic hematite in a banded iron formation of the Nuvvuagittuq Greenstone Belt in Canada; [30] graphite in 3.7 billion-year-old metasedimentary rocks in western Greenland; [31] and microbial mat fossils in 3.48 billion-year-old sandstone in Western Australia.
The evolution of photosynthesis refers to the origin and subsequent evolution of photosynthesis, the process by which light energy is used to assemble sugars from carbon dioxide and a hydrogen and electron source such as water. It is believed that the pigments used for photosynthesis initially were used for protection from the harmful effects ...
The timeline of human evolution outlines the major events in the evolutionary lineage of the modern human species, Homo sapiens, throughout the history of life, beginning some 4 billion years ago down to recent evolution within H. sapiens during and since the Last Glacial Period . It includes brief explanations of the various taxonomic ranks in ...
Gold often occurs in free elemental ( native state ), as nuggets or grains, in rocks, veins, and alluvial deposits. It occurs in a solid solution series with the native element silver (as in electrum ), naturally alloyed with other metals like copper and palladium, and mineral inclusions such as within pyrite.
Pale Blue Dot: A Vision of the Human Future in Space is a 1994 book by the astronomer Carl Sagan. It is the sequel to Sagan's 1980 book Cosmos and was inspired by the famous 1990 Pale Blue Dot photograph, for which Sagan provides a poignant description. In the book, Sagan mixes philosophy about the human place in the universe with a description ...
1831 ( MDCCCXXXI) was a common year starting on Saturday of the Gregorian calendar and a common year starting on Thursday of the Julian calendar, the 1831st year of the Common Era (CE) and Anno Domini (AD) designations, the 831st year of the 2nd millennium, the 31st year of the 19th century, and the 2nd year of the 1830s decade.
Purple has long been associated with royalty, originally because Tyrian purple dye—made from the secretions of sea snails—was extremely expensive in antiquity. [1] Purple was the color worn by Roman magistrates; it became the imperial color worn by the rulers of the Byzantine Empire and the Holy Roman Empire, and later by Roman Catholic ...