Light and Life
How Much Energy Has Life Used Since Its Beginning on Earth? 5 Days of Total Solar Output!
Life is the song of energy on its way to entropy.
Without doing the calculation, it is difficult to understand how much high quality energy the sun wastes on empty vacuum, and what a tiny fraction of it hits the earth, is absorbed by life, and is converted to biomass and "food".
- The sun emits 380 trillion terawatts.
- The earth intercepts 170 thousand terawatts.
- 120 thousand terawatts reaches the surface.
- Plants (mostly land plants) capture 20 thousand terawatts.
- Plants make about 200 terawatts of edible structure.
- Mankind's machines consume about 14 terawatts of energy, unequally distributed per capita.
Plants began to colonize the land about 500 million years ago, and have steadily expanded their range and photosynthetic variety over that time. C4 photosynthesis is a recent evolutionary "innovation", perhaps 30 million years old, so plants continue to evolve in their range and energy consumption. It is reasonable to estimate that land plants started at 0 terawatts capture 500 million years ago, and that energy capture ramped upwards linearly to the present.
From this estimate, life has captured perhaps 10 thousand terawatts times 500 million years, or 5 trillion terawatt-years, or 1800 trillion terawatt-days ( day = 86400 seconds, days were shorter a long time ago).
The sun produces 380 trillion terawatts total, so 1800 trillion terawatt-days is about 5 days of solar output.
If all the energy from the sun was devoted to life, it could support as much life in 5 days as the earth has supported since the beginning of time, the only life we know about. If life someday uses all the sun's energy, and continues to thrive as the sun increases in luminosity 5x and expands towards a red dwarf 10 billion years from now, the solar system can support 4 trillion times as much life in the future as it has up to now. If life adapts to the far reaches of the solar system, and operates at lower temperatures and higher energy-to-event thermal efficiency, the solar system might support 20 trillion times as much life as has lived before.
Past, present, and future life on earth is precious indeed, and will be the template, inspiration, and source of all life that follows. But this is just the beginning - as we expand the biosphere into artificial evolution beyond our rugged yet fragile little planet, a mighty forest of life will grow from our tiny seed. What life has done to date is magnificent, and should be protected and cherished as long as life persists, but vast expansion follows, and we are blessed with the opportunity to foster that expansion.