PDA

View Full Version : How many living cells are there on Earth?



SRH
2013-Jan-18, 11:36 PM
In a single snapshot of time...

If you were to add up every cell in your body, including all of the bacteria in your gut, plus the cells of all the people in the world, plus all of the plant, animal, bug, bacteria, virus cells living in the ocean and ground and land (and air), how many cells would that amount to?
Alternatively, how many strands of DNA or mRNA are there on Earth?

Has anyone ever tried to quantify a rough number? There is a number and it is not infinity.

SRH
2013-Jan-18, 11:40 PM
I came across this for a start...

"
How much DNA do you have in your body? A DNA base pair has a length of a little less than one nanometer (a billionth of a meter). There are approximately three billion DNA base pairs in the human genome, and since we are diploid organisms, each cell actually contains six billion base pairs. Therefore, if you took all the DNA in a human cell and stretched it out, it would reach a few meters. Now, there are about 10 trillion cells in the human body. So, all the DNA in your body, if laid end to end, would reach from the Earth to the Sun a hundred times! Yes, you read that correctly. Yes, that is a long freaking way!"

SRH
2013-Jan-19, 12:50 AM
a really rough stab at this...

radius of Earth = 6,371km
depth of life = 12km
volume of Earth that supports life = 4/3pi 6371^3 - 4/3pi 6359^3 = 0.0034x10^12 km3

human = 1m^3 = 0.001km3

# of humans in volume = 3.4x10^12
# of cells per human = 10x10^12

total living cells on Earth = 3.4x10^25

grapes
2013-Jan-19, 02:47 AM
human = 1m^3 = 0.001km3

Just a couple nits, that will change your estimate by a few magnitudes.

The human body floats, but just barely, so it is pretty close to the density of water, which is 1gm/cm3, so a one cubic meter human would weigh just a little less than 1000 kg, a metric ton. An average human weighs less than a tenth of that. So a cubic meter would have about ten times as many cells.

Also, 1m3 is not 0.001km3, it is 0.000000001km3

Those two points would change your estimate of total living cells on Earth to 3.4x1032

Swift
2013-Jan-19, 03:41 AM
The wikipedia article on biomass (http://en.wikipedia.org/wiki/Biomass_%28ecology%29) has a table of the biomass of various creatures. For Prokaryotes (bacteria) it lists the number of individuals at about 5 x 1030. That's just bacteria.

For Antarctic krill, it lists an estimate of 8 x 10 14 individuals, and krill are multi-cellular creatures.

geonuc
2013-Jan-19, 08:50 AM
a really rough stab at this...

radius of Earth = 6,371km
depth of life = 12km
volume of Earth that supports life = 4/3pi 6371^3 - 4/3pi 6359^3 = 0.0034x10^12 km3

human = 1m^3 = 0.001km3

# of humans in volume = 3.4x10^12
# of cells per human = 10x10^12

total living cells on Earth = 3.4x10^25

Are you trying to come up with a rough estimate by figuring the volume of our biosphere and calculating the number of people that would fit in it? I suppose that might do for an upper bound, but not an estimate.

Ronald Brak
2013-Jan-19, 09:47 AM
Ignore everything that isn't a procaryote (bacteria and friends) or archaea as all other life is just a rounding error. There's an awful lot of these dudes in the crust and oceans. About 500,000,000,000,000 tonnes all up, very roughly speaking. As they weigh about a 100 trillionth of a kilogram each that makes for about 500,000,000,000,000,000,000,000,000,000,000 cells, which is 5x10^32, which is pretty close to the wikipedia estimate for number of procaryotes.

NOTE: This calculation contains numbers larger than the quantity of fingers I have so I make no guarantees about its accuracy.

grapes
2013-Jan-19, 02:12 PM
The wikipedia article on biomass (http://en.wikipedia.org/wiki/Biomass_%28ecology%29) has a table of the biomass of various creatures. For Prokaryotes (bacteria) it lists the number of individuals at about 5 x 1030.

Ignore everything that isn't a procaryote (bacteria and friends) or archaea as all other life is just a rounding error. There's an awful lot of these dudes in the crust and oceans. About 500,000,000,000,000 tonnes all up, very roughly speaking. As they weigh about a 100 trillionth of a kilogram each that makes for about 500,000,000,000,000,000,000,000,000,000,000 cells, which is 5x10^32, which is pretty close to the wikipedia estimate for number of procaryotes.
I will not accept 5x10^32 as pretty close to 5x10^30 :)

That's two orders of magnitude difference!

500,000,000,000,000 tonnes is 5 x 10^14 tonnes, or 5 x 10^17 kg. If there are 100 trillion per kilogram, that's 1 x 10^14 per kilogram, and multiplying that by 5 x 10^17 kg is 5 x 10^31

Closer, but still off by an order of magnitude.


NOTE: This calculation contains numbers larger than the quantity of fingers I have so I make no guarantees about its accuracy.Fair enough :)

Swift
2013-Jan-19, 04:04 PM
NOTE: This calculation contains numbers larger than the quantity of fingers I have so I make no guarantees about its accuracy.
I would hope so, as it would be very hard to shop for gloves otherwise. :D

Jeff Root
2013-Jan-19, 08:46 PM
I usually accept one order of magnitude as "pretty close".
Not usually two.

I have been off by as much as 22 orders of magnitude.

-- Jeff, in Minneapolis

Ronald Brak
2013-Jan-20, 12:00 AM
For me, two orders of magnitude is close. It may be a personal best for me when dealing with superdigital numbers. But thanks for improving on it, Grapes.