All photosynthetic machinery seems to have evolved from a single common ancestor, a bacterium. Nature has learned that when something works, one keeps it and uses it over and over.
Trees may now take less water from the ground and need less water to grow because of rising carbon dioxide levels in the air. Far out idea? Perhaps; but not quite. How might a changing climate change forests and the interwoven ecological systems that depend on them? Are such changes common during the history of the earth? The answer is yes.
Imagine forests were to transport less water up to their leaves or needles while carbon dioxide in the atmosphere is rising. With enough time, trees might evolve resilience to drought and higher temperatures. But there’s a downside. The huge volume of water that trees pull from the ground enters the atmosphere as gas, condenses and returns to us as rain. Might trees transporting less water eventually lead to less rainfall and more desertification?
Studies suggest trees can partly close the pores in their leaves (stomates) and still take in more carbon dioxide from the atmosphere than they did just ten years ago. Remember stomates control how much water passes to the atmosphere as well as how much carbon dioxide enters the leaves during photosynthesis.
Photosynthesis now and then
The photosynthesis we learn about in school is not the only photosynthesis on the planet. Photosynthesis is what pulls water through plants. In its current form, photosynthesis in higher plants converts energy from the sun (light) into chemical energy trapped in carbohydrates that plants and animals use for food. Photosynthesis in green plants today requires water, carbon dioxide and light. Photosynthesis also releases oxygen. But it didn’t always work like this. There was no atmospheric oxygen in the very beginning. As with many natural systems exposed to a changing planet over billions of years, photosynthesis has evolved along with the earth.
The evolution of photosynthesis began with the origins of life, and changed as the earth’s climate changed. Photosynthesis evolved continually along a complex crooked path from primitive Cyanobacteria or blue green algae into the many types of photosynthetic systems we have today.
The first Cyanobacteria
Earth formed about four and a half billion years ago. It took about a billion years for the first photosynthetic bacteria to form. Starting three and a half billion years ago, these bacteria absorbed low energy infra red light and trapped this energy in molecules that contained sulfur and not oxygen. The pigments in these bacteria that trapped the energy of red light are the simplest predecessors to today’s chlorophyll.
After another billion years, about two and a half billion years ago, the atmosphere changed. Rocks from back then show evidence that the earth now had oxygen in its atmosphere. Blue green cyanobacteria were now well developed, employing a mixture of pigments including several chlorophylls to capture light.
Cyanobacteria live in water and manufacture their own food. Although cyanobacteria are small and usually unicellular, many grow in colonies large enough to see. Cyanobacteria more than three and a half billion years old form one of the largest and most important groups of bacteria.
The first hard evidence for how early photosynthesis worked comes from stromatolites in warm shallow seas in western Australia. By trapping and cementing sand grains together, slimy films of microorganisms form these layered rocky masses that look like cauliflowers. From these structures we see how cyanobacteria live and work. (Fig)
To enjoy the beauties of cyanobacteria, (also called blue-green algae) you only have to look at that moist black film along the bottom of your shower curtain. (Fig) These primitive beauties are very old and need only moisture and very little light to live and reproduce. They have been found in fossil remains from more than 3.5 billion years ago.
The next changes came when red and brown marine algae (kelp and seaweed) evolved several new forms of chlorophyll about one and a half billion years ago. Brown algae could now use shorter, more energetic wavelengths of light than Cyanobacteria. (Remember, the shorter blue violet wavelengths of light carry more energy than the longer red-infra red wavelengths.) As chlorophyll evolved and became more complicated, more and more energy could be extracted from sunlight.
Green algae evolved in shallow water where green pigments can trap more energy than red or brown algae. In today’s tide pools on rocky coasts you can find red, brown and green algae.
About half a billion years ago mosses and liverworts evolved from green algae and invaded the land. Lacking vascular tissues as well as stems and roots, these simpler plants cannot grow tall. Only 0.4 billion years ago did we get ferns, grasses, cacti and trees. All these plants contain vascular tissues that provide support and let them rise above the earth and capture more light.
The earliest photosynthetic organisms did not make oxygen as a byproduct. The photosynthetic machinery and systems for capturing light and using its energy to build molecules has changed multiple times. Once bacteria learned how to capture light and make carbohydrates, new soon-to-be plant cells acquired these photosynthetic bacteria. First these bacteria inside cells evolved to become symbiotic inside the cells of green plants. These symbiotic bacteria grew more dependent on their hosts and evolved into our contemporary chloroplasts. Today’s chloroplasts are organelles derived from bacteria in the green parts of all plants.
This ability to produce oxygen, which thenaccumulated in the atmosphere, forever changed the Earth and permitted advanced life to develop and use oxygen efficiently during respiration to break down food and carbohydrates to get the energy to grow and reproduce.
A new study presents evidence that life on earth is four times as old as we thought.
2.2 billion years old, and extends almost half way back to earth’s formation. Fossils the size
of match heads, ( Diskagama) neither plants nor animals, resemble a modern soil organism (
Geosiphon) a fungus filled with cyanobacteria. Evidence in Sept issue of journal: Precambrian Research.
Published July 23, 2013