T HERMODYNAMIC PRINCIPLES EMBODIED by the

T HERMODYNAMIC PRINCIPLES EMBODIED by the

second law and Carnot’s engine will always limit the effi- ciency of heat engines, regardless of their operation and composi- tion. But often these limits have not yet been reached, as is the case with automobile engines, and there is still room for improvement. Although the laws of thermodynamics demand that some heat

be discarded in the exhaust, a lot of heat also needlessly escapes from today’s engines and raises the temperature of the surround- ing material. Further study of heat transfer in various substances and materials may lead to better insulators and improved methods of retaining this heat, allowing it to do work instead of simply heat- ing up a car’s hood or a jet engine casing.

Thermodynamics research also holds promise in other endeav- ors, many of which involve practical engineering problems—the kind of problem that motivated the study of thermodynamics in the first place. But some of this research strikes a more fundamen- tal chord. One of the most interesting research programs involves the origin of life.

The question of life’s beginnings is controversial because for many people it is not just a question of science but also involves important religious beliefs. Science may or may not have anything to say about religion—this is also a controversial question—but most scientists today believe Earth formed about 4.5 billion years

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ago and life arose when large molecules combined and began to replicate themselves. Paleontologists (scientists who study ancient life-forms) are unsure exactly when life arose—the oldest indica- tion of life is in rocks 3.5 billion years old, but such remains are tiny, and some scientists are not certain whether these remains are really fossils of living organisms or were formed by some chemical process unrelated to life. But fossils clearly show up in 2.5-billion- year-old rocks, so life must have began billions of years ago.

If life evolved when molecules combined together and began to replicate—and assuming that no one was present to guide the pro- cess—then life sprang from self-organization. Life is an organized and orderly arrangement of matter, so in the beginning, matter escaped its normal state—disorder—and transformed itself into

a complex and orderly unit. Thermodynamics and the concept of entropy are critical in this kind of process. Self-organization might seem impossible—it would be like a city forming itself out of a forest or a house assembling itself from raw materials. Order decreases entropy, which is highly unlikely for a spontaneous process, especially a large and complex process such as a house, a city, or even a tiny single-celled organism. But only in isolated systems is entropy overwhelmingly likely to rise. Entropy and the second law of thermodynamics do not rule out orderly arrangements; these concepts merely suggest that some input of energy is necessary. Self-organization can occur if there is an external source of energy to drive the process and, taking into account the whole system—the energy source along with life’s starting materials—entropy rose. This is similar to a heat engine, which can do work and cause a local decrease in entropy as long as the process exhausts some heat into the environment so that the overall entropy will rise.

The energy source that sparked early life is not known. In 1953, American chemist Harold Urey and his student Stanley Miller performed an experiment with a sterilized flask of ammonia, meth- ane, water, and hydrogen, which they believed was similar to con- ditions on Earth billions of years ago. For an energy source they used sparks of electricity mimicking lightning. Urey and Miller opened the flasks in a few days and discovered complex molecules

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associated with life, such as amino acids. This was one of the earli- est experiments showing the formation of complex molecules from simple components.

Thermodynamics involves entropy, time, energy conversion and transfer, and is a fundamental consideration in the study and search for the origin of life. The apparent impossibility of back- ward time travel means that no one will probably ever be able to observe what really happened, so scientists must use the concepts and theories of thermodynamics, along with fossils and the prin- ciples of biology, to piece the story together.

At the present time, the origin of life is filled with mysteries. Because of experiments like those of Urey and Miller, the forma- tion of complex organic molecules—the building blocks of life—is not difficult to understand. But no one knows how these molecules organized themselves into living cells. Cells have complex arrange- ments of genes made out of DNA, proteins made from amino acids that perform many vital tasks, and a highly complex metabo- lism to convert energy in the form of food into fuel to operate life’s many tasks (a process that decreases entropy in the organism but increases entropy in the environment). How life arose from com- plex molecules is a scientific problem whose possible solutions will

be informed, and constrained, by the laws of thermodynamics.