Purple Earth

Purple Earth hypothesis

The Purple Earth hypothesis (PEH) is an astrobiological hypothesis, first proposed by molecular biologist Shiladitya DasSarma in 2007, 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 rather than its current greenish color. It is estimated to have occurred between 3.5 and 2.4 billion years ago during the Archean eon, prior to the Great Oxygenation Event and Huronian glaciation.

Earth

Earth is the third planet from the Sun and the only astronomical object known to harbor life. This is made possible by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth's water is contained in its ocean, which covers 70.8% of Earth's crust. The remaining 29.2% of Earth's crust is dry land, which is predominantly located within Earth's land hemisphere in the form of continental landmasses. Most of Earth's land is at least somewhat humid and covered by vegetation, while large ice sheets at Earth's polar deserts retain more water than Earth's groundwater, lakes, rivers, and atmospheric water combined. Earth's crust consists of slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth has a liquid outer core that generates a magnetosphere capable of deflecting most of the destructive solar winds and cosmic radiation.

Purple

Purple is a color similar in appearance to violet light. In the RYB color model historically used in the arts, purple is a secondary color created by combining red and blue pigments. In the CMYK color model used in modern printing, purple is made by combining magenta pigment with cyan pigment, black pigment, or both. In the RGB color model used in computer and television screens, purple is created by mixing red and blue light in order to create colors that appear similar to violet light. According to color theory, purple is considered a cool color.

purple

Noun

1. A colour between red and blue; violet, though often closer to magenta.
2. Any non-spectral colour on the line of purples on a colour chromaticity diagram or a colour wheel between violet and red.

Adjective

1. Of a purple hue.
2. Not predominantly red or blue, but having a mixture of Democrat and Republican support.

earth

Proper noun

1. Alternative letter-case form of Earth (“the third planet of the Solar System, upon which humans live”).

Noun

1. Soil.
2. Any general rock-based material.