| |
ZL2VAL > SETI 21.05.04 13:37l 101 Lines 4304 Bytes #999 (0) @ WW
BID : 8B0897ZL2VAL
Read: DL5DKW GUEST
Subj: It ain't easy being green
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<ON0AR<ZL2BAU<VK3KAY<SP7MGD<ZL2TZE<
ZL2AB
Sent: 040521/1118Z @:ZL2AB.#46.NZL.OC #:40753 [New Plymouth] FBB7.00g
From: ZL2VAL@ZL2AB.#46.NZL.OC
To : SETI@WW
The Case Against Litte Green Men
By Margaret Turnbull
University of Arizona
And Seth Shostak
SETI Institute
posted: 06:28 am ET
20 May 2004
Not so long ago, putative extraterrestrials were the color of moss.
Generic space aliens were inevitably described as "Little Green Men,"
probably because an avocado complexion is dramatically unlike any human
skin tint.
Green was alien, in other words.
But that idea is more than passing strange, because any glance out the
window will convince you that green is one of life's most popular colors
on our planet. Chlorophyll, the foundation of the terrestrial food
chain, is green. Most biology on Earth runs on green power, including
(indirectly) you.
However, virtually all the solar-powered life on our planet is plant
life. Animals don't seem to be interested in direct food production from
sunlight. Are they missing a bet? Is there any reason why an alien with
a green epidermis couldn't produce its food by just hanging around in
the sun?
There is. And the reason can be traced to energy efficiency. At the
Earth's surface, sunlight provides about 100 watts of power per square
meter. If you were conscious during high school biology class, you'll
recall that when this light strikes a leaf, it encourages the
combination of water and carbon dioxide into sugars. These sugars then
allow the plant to produce pollen (for reproduction), blossoms and
nectar (for pollinators), leaves (for intercepting more light), and
roots (for sucking up more water).
What most people don't know is that out of the original 100 watts
striking a square meter of leaf, only about 35% is actually absorbed.
(If the absorption were fully efficient, plants would be black.) Worse,
the photosynthetic reactions that subsequently occur with the remaining
35 watts are so inefficient that only about one-fourth of that energy
results in usable sugars. Hence for every 100 watts of perfectly good
sunlight, only about 8 watts ends up as plant food.
That means that your typical backyard bush runs on only as much power as
a bicycle headlamp, even during the day. If you're a bush, that's good
enough: you can't, and don't, scour the countryside for food, water, or
breeding partners.
But a human-sized animal can't be happy with a bush-sized energy budget.
As a typical adult, you need at least 2,000 Calories a day. Making the
conversion to less arcane units, that works out to about 100 watts of
power, 24 hours a day. But remember that if you got your energy through
photosynthesis, you would absorb only 8 watts for each square meter of
skin. Most of us have about 3 square meters of epidermis, roughly half
of which is in shade at any given time (more, if you insist on wearing
clothes). So that's just over a dozen watts of daytime power, nearly 10
times less than our burn rate. To provide the energy for one day's worth
of your gusto-grabbing lifestyle, you'd need to bake on the back patio
for three weeks.
Okay, so maybe it's not reasonable for big, mobile animals to get food
straight from the Sun. But what about smaller critters? A hummingbird,
admittedly not necessarily a good model for ET, but still an active
animal, uses about 8 Calories per day, or about a half watt. To get this
energy from 5 hours of daily photosynthesizing, this little guy would
need a collecting area of 0.3 square meters. For a creature that's only
10 cm long, the required wingspan would be three meters. That would make
for a hummer the length of a Hummer, and one unwieldy bird.
Bottom line? Animals are clever enough to let plants sit around in the
Sun all day, building up stores of energy. The wily critters then spend
a few minutes harvesting this slow work as a salad - or chowing down on
other animals that have already dined on salads. It's all a matter of
energetics, and you can bet that many extraterrestrials will have the
same strategy.
Frankly, if you're an animal, it isn't easy being green.
=========================
73 de Alan, (Sysop ZL2AB).
AX25:ZL2VAL@ZL2AB.#46.NZL.OC
IP :zl2val@qsl.net
APRS:!3903.34S/17406.45E]
Message timed: 23:03 on 2004-May-21 (NZT)
Message sent using WinPack-AGW V6.80
Points to ponder
~~~~~~~~~~~~~~~~
Rural wisdom
------------
Don't corner something meaner than you.
Read previous mail | Read next mail
| |
