Experiments usually have several controlled variables. These are variables that must be kept constant in all parts of an experiment. For example, if an experiment is testing the effect of sunlight on the growth rate of 5 seeds, the only variable that should change should be the amount of sunlight. All other variables should remain the same to ensure that sunlight is the only aspect affecting the results. The other variables, such as soil type, amount of water, type/amount of fertilizer, are the controlled variables. Looking back at the simulation experiment on the meteorite, describe two variables that should have been controlled. Apr. 4, 2013 – Researchers at the University of Leeds may have solved a keypuzzle about how objects from space could have kindled life on Earth.While it is generally accepted that some important ingredients for life came frommeteorites bombarding the early Earth, scientists have not been able to explainhow that inanimate rock transformed into the building blocks of life.This new study shows how a chemical, similar to one now found in all living cellsand vital for generating the energy that makes something alive, could have beencreated when meteorites containing phosphorus minerals landed in hot, acidicpools of liquids around volcanoes, which were likely to have been commonacross the early Earth."The mystery of how living organisms sprung out of lifeless rock has long puzzledscientists, but we think that the unusual phosphorus chemicals we found couldbe a precursor to the batteries that now power all life on Earth. But the fact thatit developed simply, in conditions similar to the early Earth, suggests this couldbe the missing link between geology and biology," said Dr Terry Kee, from theUniversity's School of Chemistry, who led the research.All life on Earth is powered by a process called chemiosmosis, where thechemical adenosine triphosphate (ATP), the rechargeable chemical 'battery' forlife, is both broken down and re-formed during respiration to release energyused to drive the reactions of life, or metabolism. The complex enzymes requiredfor both the creation and break down of ATP are unlikely to have existed on Earthduring the period when life first developed. This led scientists to look for a morebasic chemical with similar properties to ATP, but that does not require enzymesto transfer energy.Phosphorus is the key element in ATP, and other fundamental building blocks oflife like DNA, but the form it commonly takes on Earth, phosphorus (V), is largelyinsoluble in water and has a low chemical reactivity. The early Earth, however,was regularly bombarded by meteorites and interstellar dust rich in exoticminerals, including the far more reactive form of phosphorus, theiron-nickel-phosphorus mineral schreibersite.The scientists simulated the impact of such a meteorite with the hot,volcanically-active, early Earth by placing samples of the Sikhote-Alin meteorite,an iron meteorite which fell in Siberia in 1947, in acid taken from the Hveradalurgeothermal area in Iceland. The rock was left to react with the acidic fluid in testtubes incubated by the surrounding hot spring for four days, followed by afurther 30 days at room temperature.In their analysis of the resulting solution the scientists found the compoundpyrophosphite, a molecular 'cousin' of pyrophosphate -- the part of ATPresponsible for energy transfer. The scientists believe this compound could have In their analysis of the resulting solution the scientists found the compoundpyrophosphite, a molecular 'cousin' of pyrophosphate -- the part of ATPresponsible for energy transfer. The scientists believe this compound could haveacted as an earlier form of ATP in what they have dubbed 'chemical life'."Chemical life would have been the intermediary step between inorganic rockand the very first living biological cell. You could think of chemical life as amachine -a robot, for example, is capable of moving and reacting tosurroundings, but it is not alive. With the aid of these primitive batteries,chemicals became organised in such a way as to be capable of more complexbehaviour and would have eventually developed into the living biologicalstructures we see today," said Dr Terry Kee.The team from NASA's Jet Propulsion Laboratory (JPL-Caltech) working on theCuriosity rover, which landed on Mars in August last year, has recently reportedthe presence of phosphorus on the Red Planet."If Curiosity has found phosphorus in one of the forms we produced in Iceland,this may indicate that conditions on Mars were at one point suitable for thedevelopment of life in much the same way we now believe it developed onEarth," added Dr Kee.The team at Leeds are now working with colleagues at JPL-Caltech to understandhow these early batteries and the 'chemical life' they became part of might havedeveloped into biological life. As part of this work they will be using facilities inthe University of Leeds' Faculty of Engineering, currently used to test new fuelcells, to build a 'geological fuel cell' using minerals and gases common on theearly Earth. Researchers will apply different chemicals to its surface and monitorthe reactions take place and the chemical products which develop.The team also hope to travel to Disko Island in Greenland which is home to theEarth's only naturally-occurring source of schreibersite, the mineral found in theSikhote-Alin meteorite. Here, they hope to repeat their experiments and showthat the same chemicals develop in an entirely Earth-originated setting.Story Source:University of Leeds (2013, April 4). Origin of life: Power behind primordial soup discovered.ScienceDaily. Retrieved June 4, 2013, fromhttp://www.sciencedaily.com/releases/2013/04/130404122234.htmJournal Reference:David E. Bryant, David Greenfield, Richard D. Walshaw, Benjamin R.G. Johnson, Barry Herschy,Caroline Smith, Matthew A. Pasek, Richard Telford, lan Scowen, Tasnim Munshi, Howell G.M.Edwards, Claire R. Cousins, lan A. Crawford, Terence P. Kee. Hydrothermal modification of theSikhote-Alin iron meteorite under low pH geothermal environments. A plausibly prebiotic routeto activated phosphorus on the early Earth. Geochimica et Cosmochimica Acta, 2013; 109: 90 DOI:10.1016/j.gca.2012.12.043

A control variable is the one which is kept constant throughout the experiment. This is important in…

Answered: Experiments usually have several…

11th Edition

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Chapter1: The Human Body: An Orientation

Section: Chapter Questions

Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...