life summary

Learn about the origin and evolution of life

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Below is the article summary. For the full article, see life.

*Streptococcus pyogenes*
Scanning electron micrograph of *Streptococcus pyogenes*, associated with strep throat and scarlet fever.

life, Matter characterized by the ability to metabolize nutrients (process materials for energy and tissue building), grow, reproduce, and respond and adapt to environmental stimuli. The oldest fossil evidence of Earth’s first living organisms, bacteria and cyanobacteria, dates to about 3.5–3.7 billion years ago. All known life-forms possess either DNA or RNA. Viruses, which possess DNA and RNA, cannot reproduce without a host cell and do not metabolize nutrients, and it is uncertain whether they should be classified as living or nonliving. Scientists disagree on the likelihood of extraterrestrial life. See also Drake equation.

arbovirus Summary

Arbovirus, acronym derived from arthropod-borne virus, any of a group of RNA viruses that develop in arthropods (chiefly blood-sucking mosquitoes and ticks), in which they cause no apparent harm, and are subsequently transmitted by bites to vertebrate hosts, in which they establish infections and

aphasia Summary

Aphasia, defect in the expression and comprehension of language caused by damage to the temporal and the frontal lobes of the brain. Aphasia can be caused by a head injury, a tumour, a stroke, or an infection. Symptoms vary with the location and extent of the brain tissues involved. Damage to the

germination Summary

Germination, the sprouting of a seed, spore, or other reproductive body, usually after a period of dormancy. The absorption of water, the passage of time, chilling, warming, oxygen availability, and light exposure may all operate in initiating the process. In the process of seed germination, water

livestock Summary

Livestock, farm animals, with the exception of poultry. In Western countries the category encompasses primarily cattle, sheep, pigs, goats, horses, donkeys, and mules; other animals, such as buffalo, oxen, llamas, or camels, may predominate in the agriculture of other areas. By the 21st century,