In 2009, a satellite orbited Earth, systematically scanning and sorting the wavelengths reflected off the planet's surface.
Researchers were looking for the spectral signature of carbon dioxide when they noticed something surprising:
An unexpected wavelength of unknown origin.
They tried looking at Earth with only this wavelength, and saw the planet covered in varying degrees of red. It could not reflect sunlight because it was a wavelength that never leaves the Sun's outer atmosphere.
And it was inconsistent with densely populated areas, suggesting it wasn't even man-made. In fact, it was coming out of a lot of vegetated places: the Amazon basin, the northern evergreen forests, and the croplands of the American Midwest were all burning.
Photosynthesis So, what was happening? Plants and other organisms use light to grow through photosynthesis. But this is only one of three ways in which the light that enters photosynthetic organisms is used.
And this is the key to solving the mystery.
To understand the others, we need to start with photosynthesis. During this process, sunlight hits structures inside plant cells called chloroplasts, which are filled with the pigment chlorophyll.
When chlorophyll molecules absorb light, some of their electrons become excited. They undergo a series of reactions, which convert light energy into chemical energy.
It gives the energy to convert carbon dioxide and water into glucose, the simple sugar plants need to grow.
And of course, this reaction produces an important byproduct. Photosynthesis - carried out continuously by plants, algae and bacteria - produces all of Earth's oxygen. But plants regularly absorb more light than they can use.
For example, during winter, frozen leaves of evergreen trees cannot photosynthesize at their normal rate, but are still exposed to a lot of sunlight. If not dealt with, too much light can damage their photosynthetic machinery.
So, another way plants use light is to convert it into heat and expel it from their leaves. A third way plants interact with incoming light is by re-emitting it at a different wavelength to produce chlorophyll fluorescence.
During photosynthesis,
the excited electrons of chlorophyll go through this series of chemical reactions. But when some of the excited electrons fall back to their ground states, they emit energy as light.
Overall, about 1% of the absorbed light is re-emitted as wavelengths at the red end of the spectrum. Chlorophyll fluorescence is so small that you cannot see it with the naked eye.
But plants around the world are fluorescing because they photosynthesize. And this is what causes the Earth's astonishing red glow, as observed by satellites. It was an accidental discovery, but a huge breakthrough.
Detecting chlorophyll fluorescence from space allows us to see the planet breathing in real time and monitor the health of ecosystems worldwide. Previously, researchers used vegetation level as a primary predictor of plant health.
Since plants usually change color or lose foliage when they are stressed,
a high level of green usually indicates healthy plants. But this measure can be unreliable. In contrast, chlorophyll fluorescence is a direct measure of photosynthetic activity.
This can help us estimate how much oxygen is being released into a system and how much carbon is being absorbed. Drops in chlorophyll fluorescence can precede visible signs of plant stress, making this a timely measure.
Scientists have already used chlorophyll fluorescence to monitor harmful phytoplankton blooms and detect the effects of drought in the Amazon and Great Plains.
Moving forward, we'll investigate photosynthesis from space, and figure out how to help our silent friends, who already do so much for us.
Comments
Post a Comment