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Nitrogen is a chemical element; it has symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System.
The timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth.Dates in this article are consensus estimates based on scientific evidence, mainly fossils.
Under low oxygen concentrations and before the evolution of nitrogen fixation, biologically-available nitrogen compounds were in limited supply, [16] and periodic "nitrogen crises" could render the ocean inhospitable to life. [9] Significant concentrations of oxygen were just one of the prerequisites for the evolution of complex life. [9]
Nitrogen assimilation is the formation of organic nitrogen compounds like amino acids from inorganic nitrogen compounds present in the environment. Organisms like plants, fungi and certain bacteria that can fix nitrogen gas (N 2) depend on the ability to assimilate nitrate or ammonia for their needs. Other organisms, like animals, depend ...
One ancient view of the origin of life, from Aristotle until the 19th century, is of spontaneous generation. [19] This theory held that "lower" animals such as insects were generated by decaying organic substances, and that life arose by chance. [20] [21] This was questioned from the 17th century, in works like Thomas Browne's Pseudodoxia ...
The history of life on Earth traces the processes by which living and extinct organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as Ga, for gigaannum) and evidence suggests that life emerged prior to 3.7 Ga. [1] [2] [3] The similarities among all known present-day species indicate that they have diverged through the ...
A man convicted for the brutal slaying of hitchhiker Vickie Lynn Deblieux in 1994 is scheduled to be executed with nitrogen gas by the state of Alabama on Thursday.. Carey Daley Grayson, 49, was ...
c. 560 Ma – Trace fossils, e.g., worm burrows, and small bilaterally symmetrical animals. Earliest arthropods. Earliest fungi. c. 558 Ma – Dickinsonia, a large slow moving disc-like creature, first appears – the discovery of fat molecules in its tissues make it the first confirmed true metazoan animal of the fossil record.