Skye, Arkensaw asked:
I was taught when I was young that we drink the same water today that the dinosaurs drank when they were alive, is that true?
Professor Ken Carslaw, Atmospheric Science, University of Leeds:
Water is recycled through the water cycle. It evaporates from the oceans, forms clouds, it rains (or snows), the rivers return the water to the ocean. The longest timescale of water anywhere in the cycle is in the deep ocean (it stays there for several thousand years) and in deep ground water (perhaps 10,000 years). However, water is very slowly destroyed chemically in photosynthesis (plants converting carbon dioxide and water to sugars and oxygen) and recovered again in respiration (basically the reverse of photosynthesis to make energy and CO2). You can calculate how much water remains from the dinosaur age from the total amount of water on the planet and the amount of water taken up in photosynthesis per year. The Earth's plants take up about 12,000 billion kg of water per year (we know that roughly from the CO2 they take up). The total water on Earth is about 1400 billion billion kg. So within about 100 million years most of the water will have been chemically destroyed. Dinosaurs lived 65 million years ago. So, SOME of the water we drink is the same water, but more than half is different water.
I think the water that's around today was around when dinosaurs were toodling about. Whether we are drinking the same water as them is a different matter. What they drank could be at the bottom of the Pacific Ocean by now.
Some of the water excreted by a plant or animal will have been created in that organism by respiration.
Given the water cycle, that is, it evaporates due to the heat of the sun, condences and forms clouds, then falls to the Earth as precipitation, it could be argued that it is the same water going round and round. Then again, it could equally be argued that, as it has been converted into gases (oxygen and hydrogen) and reformed, it is not the same. I think this depends on your point of view. rhade, Thu, 24th Jul 2008
Extremely unlikely. Water reacts in numerous ways in nature. It reacts with rocks and other materials to form oxide, hydroxides, etc. It also is consumed in biological systems and is incorporated into the living tissue in various molecular forms or excreted in some form back into nature. The odds of the exact H atoms recombining with the exact same O atom is extremely remote. Will, Sat, 26th Jul 2008
Thanks Will, and welcome, by the way! chris, Sat, 26th Jul 2008
Well that told me DoctorBeaver, Sat, 26th Jul 2008
I had one more consideration after hearing the expert answer on your program yesterday. If you consider "one water molecule" to be the exact same three atoms bonded together, then the idea that water molecules are created and destroyed through photosynthesis and respiration is correct. That process also involves changing the oxidation state of the atoms - they gain and lose electrons O2-(formal oxidation state in water) ↔ 1/2 O2(g) + 2 e-.
Nice point, I'd not considered that at all. If you do do the calculation, please let us know the result...
All of the processes that replace old water molecules with new ones are dilution processes. What this means is that not every water molecule broken down through photosynthesis or some other chemical process needs to be one of the molecules that was around at the time of the dinosaurs. Many of the molecules will come from the countless generations of new molecules formed since the time of the dinosaurs. In fact, as time goes on and the total number of "new" molecules grows, the likelihood that a reaction involves a new molecule versus an dino-vintage molecule grows.
That's a fantastic answer, thanks. Can't believe it didn't occur to me.
Thanks for all this fantastic Information. I can go and do my show at Hampshire water festival tomorrow and safely say that some of the Earth's water today was around when Dinosaurs roamed the planet.
Could it be argued that no water molecule is the same from one second to the next, even in a stable body of water, since water is subject to hydrogen bonding?
Its true.I heard this news that water changes always.