Matters of Scale - The Measure of All Things

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Estimated number of human cells in an average human body
100,000,000,000,000
Number of bacteria cells in and on an average human body
1,000,000,000,000,000
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Total biomass of oceanic cyanobacteria
~44,000,000,000
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Total biomass of humans, metric tons
~250,000,000
Total biomass of Antarctic krill
~500,000,000
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Age of the horseshoe crab
300,000,000+
Age of the cyanobacteria
3,500,000,000+
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Age of human species (homo sapiens sapiens), years
~130,000
Average age of a mammalian species at extinction
~5,000,000
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Number of species estimated by Linnaeus (1758)
~20,000
Number of species recorded today
~1,500,000
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Estimated total number of species
4,000,000 to 100,000,000
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Number of planets conceived of (in Europe) in 1500
7
Estimated number of Earth-like planets in the universe in 2005
~3,000,000,000,000,000,000,000
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Assumed distance of humanity from the center of the Universe (Earth) in the time of Copernicus (1473–1543), kilometers
0
Assumed distance of humanity from the center of the Universe (the Sun) in the time of Galileo (1564–1642), kilometers
~149,000,000
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Current estimated distance from Earth to the center of the Milky Way galaxy, light years
8,000
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Sources: Distances: University of Arizona, Educational Resources in Astronomy and Planetary Sciences website (http://ethel.as.arizona .edu/~collins/astro/index.html). Planets: Dr. Charles Lineweaver, Planetary Science Institute, Australian National University. Number of species: Prof. John Blamire, City University of New York, and Society for Conservation Biology. Species ages: Wrangham and Peter-son, Demonic Males, and Kentucky Geological Survey classroom activities website (www .uky.edu/KGS/education/timeline_short.html). Biomass: Biology Daily website (www.biol ogydaily.com/biology/Biomass), and J. Overmann and F. Garcia-Pichel in The Prokaryotes (http://141.150.157.117:8080/prokPUB/index.htm). Cells: www.nationmaster.com/ encyclopedia/Bacteria_in_the_human_body. Visit www.worldwatch.org/ ww/mos/ to view other archived Matters of Scale.