http://www.universetoday.com/92299/guest-post-the-cosmic-energy-inventory/

– Kepler gives ~ 600 terrestrials (assuming 1/2 of superEarths are not neptunians) out of ~ 2 300 candidates. Assuming the former are ~ 5 times Earth mass and the latter are mostly neptunians of ~ 20 times Earth mass, we have ~ 1/10 of planetary mass in terrestrials.

– Kepler gives ~ 50 candidates in the habitable zone, or ~ 2 %. Hence ~ 0.002 of planetary mass is in habitable terrestrials.

– Assuming conservatively an inefficient abiogenesis process we could estimate the fraction of inhabited habitables to ~ 50 % after some billion years. The fraction of stars that leave the main series before that is minute; the fraction of stars that aren't that old is relatively small. Hence ~ 0.001 of planetary mass is in inhabited planets.

– Earth mass is ~ 6*10^24 kg. The carbon cycle keeps ~ 5*10^9 kg in cells, ~ 15*10^9 kg in soils, ~ 40 000*10^9 kg in the oceans, and ~ 0.0001*5*10^18 = 500 000*10^9 kg in the atmosphere (by molar weight) , all of which are cycled by life.

Water content of a cell is ~ 50 – 80 %.

Hence, adding carbon and water under the assumption of equal rates, ~ 2*10^-10 of an inhabited planet's mass is cycled by CHNOPS cells.

Hence, rounding to nearest power, ~ 10^-13 of planetary mass is invested in life.

[All data sources, except on cell water content, are Wikipedia.]

We can note that a similar amount of the sun irradiation of 10^-10 (IIRC) of the planet energy budget is what drives the carbon cycle. So it doesn't change the local energy estimate much going between mass and energy considerations. Or, in other words, life is energy constrained, as it should be if we did the estimate correctly.

**Putting it all together ~ 10^-19 of the cosmic energy inventory consists of life.**

As a comparison, I googled that the human body has ~ 10^14 cells. Life is rarer than the happenstance kicked up soil bacteria that settles on our skin.

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Since we are doing inventories anyway, I have stumbled on a similar interesting one from the recent FQXi conference on Time.

The pity version of life is that it is a means to relax more redox energy from hydrogenating carbon dioxide into methane by the assistance of organic catalysts.

But the other end is more interesting outside of abiogenesis concerns, since the oxygenating redox energy ends up in unintuitive ways in the following inventory:

~ 75 % of the oxidation is taking iron(II) oxide (FeO; wüstite) over

iron(II,III) oxide (Fe3O4; magnetite) into iron(III) oxide (Fe2O3; hematite).

~ 25 % of the oxidation is with sulfur.

~ 1-2 % of the oxidation is resulting in free oxygen.

[Note that all these materials are common on wet terrestrials, with Fe and S cores.]

Life is how to efficiently make Fe2O3 or – rust. (O.o)