Flying over a desert area in an airplane, two scientists looked down with trained eyes at trees and bushes. After an hour’s flight one of the scientists wrote in his book, “Look here for probable metal.” Scientists in another airplane, flying over a mountain area, sent a message to other scientists on the ground, “Gold possible.” Walking across hilly ground, four scientists reported, “This ground should be searched for metal.” From an airplane over a hilly wasteland a scientist sent back by radio one word: “Uranium.”

None of the scientists had X-ray eyes: they had no magic power of looking down below the earth’s surface. They were merely putting to use one of the newest methods of locating minerals in the ground…trees and plants as signs that certain minerals may lie beneath the ground on which the trees and plants are growing.

This newest method of searching for minerals is based on the fact that minerals deep in the earth may affect the kind of bushes and trees that grow in the surface.

At Watson Bar Greek, a brook (小溪) six thousand feet high in the mountains of British Columbia, Canada, a mineral search group gathered bags of tree seeds. Boxes were filled with small branches from the trees. Roots were dug and put into boxes. Each bag and box was carefully marked. In a scientific laboratory the parts of the forest trees were burned to ashes and tested. Each small part was examined to learn whether there were minerals in it.

Study of the roots, branches, and seeds showed no silver. But there were small amounts of gold in the roots and a little less gold in the branches and seeds. The seeds growing nearest to the tree trunks had more gold than those growing on the ends of the branches.

It is universally accepted as one of life’s bleak but unavoidable facts: as we get older, our brains get slower. But now a study, based on data from more than 1 million people, suggests that mental processing speed remains almost constant until the age of 60.

The analysis puts perceived (感知的) reductions in speed down to people becoming more careful as they get older. This could account for the large body of research that has concluded that mental processing speed peaks at about the age of 20 and undergoes a steady decline from that point onwards.

“Our finding is encouraging, as our results show that average levels in mental speed in contexts demanding fast and forced decisions do not decline until rather late in the lifespan,” said Dr Mischa Von Krause, of Heidelberg University.

The study, published in the journal Nature Human Behaviour, used data from 1, 185, 882 participants, aged 10 to 80 years, in Harvard’s Project Implicit, an online tool that has been used to collect data. Participants are required to answer some questions.

The analysis suggested that 20-year-olds were quickest because they were the most willing to trade accuracy for speed. The researchers concluded that the purely mechanical part of the response (how fast a person sees the question and taps the keyboard) was quickest in those aged 14-16. Mental processing state appeared to peak at about age 30, and declined only very slightly between 30 and 60. Participants also made fewer mistakes as they became older, at least until the age of about 60.

Von Krause said the work raised the suggestion that people may excel (擅长) at different tasks depending on their age. “Obviously, there are real-life tasks where it is crucial to avoid mistakes, such as in a medical diagnosis, while in other tasks, such as avoiding an obstacle on the road, speed is more important,” he said. However, he added that, within certain limits, people were likely to be able to adapt their decision-making style to the demands of a situation.

No one knows for sure when advertising first started. It is possible that it grew out of the discovery that some people did certain kinds of work better than others did them. That led to the concept of specialization, which means that people would specialize, or focus, on doing one specific job.

Let's take a man we'll call Mr. Fielder, for example. He did everything connected with farming. He planted seeds, tended the fields, and harvested and sold his crops. At the same time, he did many other jobs on the farm. However, he didn't make the bricks for his house, cut his trees into boards, make the plows, or any of the other hundreds of things a farm needs. Instead, he got them from people who specialized in doing each of those things.

Suppose there was another man we shall call Mr. Plowright. Using what he knew about farming and working with iron, Mr. Plowright invented a plow that made farming easier. Mr. Plowright did not really like farming himself and wanted to specialize in making really good plows. Perhaps, he thought, other farmers will trade what they grow for one of my plows.

How did Mr. Plowright let people know what he was doing? Why, he advertised, of course. First he opened a shop and then he put up a sign outside the shop to attract customers. That sign may have been no more than a plow carved into a piece of wood and a simple arrow pointing to the shop door. It was probably all the information people needed to find Mr. Plowright and his really good plows.

Many historians believe that the first outdoor signs were used about five thousand years ago. Even before most people could read, they understood such signs. Shopkeepers would carve into stone, clay, or wood symbols for the products they had for sale.

A medium, in advertising talk, is the way you communicate your message. You might say that the first medium used in advertising was signs with symbols. The second medium was audio, or sound, although that term is not used exactly in the way we use it today. Originally, just the human voice and maybe some kind of simple instrument, such as a bell, were used to get people's attention.

A crier, in the historical sense, is not someone who weeps easily. It is someone, probably a man, with a voice loud enough to be heard over the other noises of a city. In ancient Egypt, shopkeepers might hire such a person to spread the news about their products. Often this earliest form of advertising involved a newly arrived ship loaded with goods. Perhaps the crier described the goods, explained where they came from, and praised their quality. His job was, in other words, not too different from a TV or radio commercial in today's world.