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Which came first, the root or the leaf?

By Mark Renz

Think you're the patient type? Try being a plant and waiting 50 million years for a chance to show what you've got. That's right. Plants had buds and the genetic potential to grow true leaves for 50 million years before they actually grew them. The reason for their wait: Carbon dioxide in Earth's atmosphere was way too high.

Did plants know what level of carbon dioxide was needed and waited patiently, or were buds just one of many green tricks they had up their tissued sleeves so it didn't matter if the atmosphere changed or not?

Had they developed full leaves when their buds first evolved, they could have grown faster and taller with more offspring. But leaves exposed to the sunlight will overheat. To cool them down, leaves need water evaporating through channels on their surface known as stomata. The process is similar to our skin allowing us to cool down by sweating.

Once the level of carbon dioxide in our atmosphere began to drop about 380 million years ago, Earth's temperatures also dropped. Ferns and seed plants began to sprout leaves which became longer and wider, and included more stomata.

But before plants developed leaves, their roots evolved. Moss and liverworts don't need the roots since they can soak up water on the ground. But roots allow a plant to travel and explore, searching for just the right amount of water and nutrients. In the process, they erode rocks and build soil. Carbon dioxide dissolved in rainwater can then react with the freshly exposed rock. Some of this carbon was moved by rivers downstream to the ocean floor where it could no longer rise to the atmosphere.

The drop in carbon dioxide levels would eventually be significant enough for leaves to begin evolving. Earth cooled more. As leaves evolved, so did trees, which got larger and were able to trap more carbon, lowering Earth's thermostat even more.

(Plant science gleaned from essayist Carl Zimmer's July 4, 2004 Scienceblogs.com essay, “Dawn of the Leafy Age.” Zimmer got his science from a July 2004 on-line paper called “Broad leaves evolved as carbon dioxide fell” (Anna Gosline), published at the Proceedings of the National Academy of Sciences, Volume 101 page 10360.)

Luck, skill, tenacity or design?

When I think of the implications here, it boggles my mind. Was this Cosmic luck, long term tenacity, or did plants knowingly and skillfully manipulate Earth's atmosphere to their advantage? Or, do my religious friends have it right when they claim this process is another perfect example of Intelligent Design? For me, the skeptic, my first response is, “What does the science suggest? Do such questions lead to testable answers?”

It would be remarkable if plants knowingly plotted a world take-over when they first evolved hundreds of millions of years ago, and we happened to become an eventual beneficiary. I cannot imagine my world without green – especially when I consider how much we rely on plants for food and nutrition, or for cutting wood for shelter and warmth, or to extract medicines.

But then in the last 200 years --a mere wink of a geological eye --it is we humans who are knowingly or perhaps without due care, taking over Earth's surface, oceans and atmosphere to the detriment of plants and other life forms. It is evident by our numbers and activities, that we are clearing far more of Earth's greenery than we replant. Instead of allowing our natural green coolants to do their jobs, we are contributing instead to a planet that – according to most climatologists – is beginning to overheat and start working against us.

With plants, even a lucky global take-over is just short of miraculous, given all the variables and competition among life forms. If they are intelligent and smart enough to not only solve problems but plan their future, what does that say for other life forms? Is there a level of intelligence in everything?

At the International Laboratory of Plant Neurobiology near Florence, Italy, Professor Stefano Mancuso runs the only laboratory devoted to plant intelligence. In an Oct 30, 2010 “Wired.com” interview with Nicole Martinelli, Professor Mancuso said he was working to debunk the notion that plants are not intelligent.

“If you define intelligence as the capacity to solve problems, plants have a lot to teach us," says Mancuso, "Not only are they 'smart' in how they grow, adapt and thrive, they do it without neuroses (mental disorders such as stress). Intelligence isn't only about having a brain."

"Plants communicate via chemical substances," Mancuso adds. "They have a specific and fairly extensive vocabulary to convey alarms, health and a host of other things. We just have sound waves broken down into various languages. I don't see how we could bridge the gap."


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