Practice Test

Using Fire to Keep a Prairie Healthy

Inside the 40,000-acre Joseph H. Williams Tallgrass Prairie Preserve in northern Oklahoma, herds of bison roam on the scenic land that is home to hundreds of different species of plants and animals. While one of the greatest threats to the prairie is wildfire, the use of controlled fires is actually an effective way to protect this idyllic landscape.

Fires that are started by lightning or other natural circumstances are inevitable, and the results can be disastrous. However, hundreds of years ago the American Indian people who inhabited the Great Plains area between Minnesota and Texas realized that these fires could also be helpful. The bison in the area seemed to prefer grazing on tender new grass on the recently burned land rather than on grass in the unburned areas. The American Indian people began to deliberately burn areas of land for bison to graze on, which enticed the herds away from the people’s crops.

Today conservationists at the Tallgrass Prairie Preserve and farmers in the Great Plains continue to use controlled burns for land management. Intentionally burning a portion of land can dramatically improve the quality of the vegetation that regrows there. The fires burn away weedy undergrowth and help limit the overcrowding of shrubs and trees in the burn area, creating less competition for water and nutrients. Additionally, the process of burning excess plant matter adds nitrogen, an essential element for plant growth, to the soil.

One common target of controlled burns at the preserve and the surrounding area is the invasive red cedar tree. A single red cedar tree can consume up to 40 gallons of water per day, taking this vital resource away from other plant life. These tall trees also cast shade that prevents sunlight from reaching the plants beneath them. The fast-growing red cedar trees tend to crowd out prairie grasses, the primary food source for wild and domestic animals that make the prairie their home. An imbalance in one component of the prairie’s ecosystem affects the entire web of life. Controlled burns help maintain this ecosystem’s delicate balance.

Of course, these controlled fires are intended to burn only a portion of an area. A total burn, which is a risk with an uncontrolled wildfire, would destroy all wildlife as well as the crops farmers plant for income. The key to using controlled fires is knowing which areas of land to burn and when. Conservation experts at the preserve employ the “patch-burn” approach, meaning they rotate which portion of land is burned each year. They study the land to find out which areas would most benefit from being burned, and then they arrange about a dozen burns over one-third of the land. This patch burning contains the fire within a specific area and allows animals in the burn area to safely relocate. The following year, conservationists will burn a different section of the preserve, while the land burned the previous year regrows healthier than before.

Researchers have tracked and studied the variety of plant species and animals that live on the preserve, and their studies show that the patch-burn approach has restored biodiversity to the area by promoting the growth of species that were at risk of being crowded out. The patch-burn system is so successful that the conservationists at the preserve provide training to prairie farmers about conducting controlled burns on their own land. Burning land to make it healthy may seem counterintuitive, but strategic controlled fires have helped the prairie sustain life for hundreds of years and, with careful management, will continue to do so.

Excerpt from “Growing Peppers on the ISS Is Just the Start of Space Farming”

by Melanie Canales

The author, Melanie Canales, is a first-generation Peruvian American farmer and beekeeper based in Virginia’s Shenandoah Valley, on lands of the indigenous Monacan and Manahoac tribes. Her work focuses on creating healthy relationships between people and their surrounding ecosystems.

Unburdened by the constraints of gravity, red and green peppers jut out at 45-degree angles inside the Advanced Plant Habitat (APH), a sort of space terrarium not much larger than a microwave. Four chile pepper plants stand effortlessly upright, despite the dozens of glossy fruits weighing them down. These plants have lived entirely in space; their leaves have never been chewed on by insects or rustled by a summer breeze, [and] their stems are unfamiliar with bending toward the sun’s arc across the sky. Scissors glint under the tank’s white and blue lights as astronaut Mark Vande Hei and his team snip the stems of those that are ready for harvest. The peppers whirl around their heads until the astronauts catch them and tape them against a board to photograph.

Back on Earth, the Plant Habitat-04 team of engineers and plant scientists are observing and conferring with the astronauts. Of the 26 peppers in this batch, only the 14 finest will stay on the International Space Station [ISS] for consumption. The rest will be wrapped in foil, sealed in a Ziploc bag, then frozen at a brisk −80 degrees, until they can come roaring back to Earth in the next cargo capsule to be studied later. Now, after a 137-day growth cycle, the astronauts remove the plants from the module and trash them. Project Plant Habitat-04 is complete. It’s taco night on the ISS.

Since 2014, NASA¹ has experimented with growing lettuces, brassicas,² and zinnias³ in space, an endeavor that relies on highly specialized technology over 50 years in the making. [Fall 2021’s] two successful pepper harvests . . . will provide data on the nutritional and psychological benefits of growing vegetables on-craft, as well as a crop’s ability to reliably produce long-term in microgravity. While controlled environmental agriculture is not new, the APH experiment represents an evolution in specialized growth habitats. It doesn’t aim to re-create Earth’s conditions, but to perfect each isolated variable of plant growth in the clinical environment of a spaceship.

“The Advanced Plant Habitat is the most complex plant growth system on orbit today,” says Lashelle Spencer, a plant scientist at NASA’s Kennedy Space Center. Its more than 180 sensors control and monitor temperature, humidity, and carbon dioxide. The astronauts can adjust the color and intensity of the light, and how much moisture the plants’ roots are getting. It waters itself.

It’s the day after Thanksgiving, and Spencer has been at Kennedy since 5 a.m. to facilitate the peppers’ final harvest. As part of the project team, she played a crucial role in preparing the seeds that were sent hurtling into space in June and guiding the astronauts through maintaining the plants in orbit. . . . Though astronauts can spend upwards of 100 days in space, their on-mission meals come dehydrated and pre-packaged; their vitamins and minerals are isolated in supplements, which lose nutritional value the longer they’re stored. Spencer’s goal is to create the conditions necessary for cultivating healthy plants in space, so those plants can sustain healthy astronauts on long-term missions. Astronaut food is great, she says—“especially the shrimp cocktail. But you’re missing that crunch. You’re missing that fresh pop of flavor, the green flavor that’s not there in that packaged food.”

The sensory experience of growing productive crops can also help mitigate⁴ the psychological effects of long-term space travel. . . . Spencer says the team cracked open the door of the APH every day to observe their vegetable companions with all the tenderness of home gardeners. When harvest day came, they batted their bounty around the ISS, taking selfies and delighting in watching the fruits pirouetting around the spacecraft. . . .

“We were thinking no heat, so that [the peppers] wouldn’t be dangerous, but maybe the astronauts need a little spice in their life,” says Paul Bosland, who along with his colleagues at the Chile Pepper Institute genetically engineered⁵ the NuMex Española Improved chile pepper seeds grown in Plant Habitat-04. . . .

Working with NASA, Bosland cultivated a variety that could accommodate both the nutritional needs of astronauts as well as the logistics of growing a plant in space. . . .

. . . The experiment is helping gather the data necessary to determine the nutritional content of crops grown in space, and therefore how many people they can feed, and for how long. Though much is still unknown, Spencer is certain of one thing that future astronauts will need to do: “I think in an optimal world, a scientist like me would say that they would be growing plants from day one. From the day they left to the day they came back, they would be growing them.”

From “Growing Peppers on the ISS Is Just the Start of Space Farming” by Melanie Canales from WIRED, December 21, 2021. Copyright © 2021 Condé Nast. All rights reserved.

¹NASA: National Aeronautics and Space Administration

²brassicas: a large genus of herbs, such as broccoli and cabbage

³zinnias: a genus of herbs and low shrubs that have flowers at their heads

⁴mitigate: to make something less severe or harmful

⁵genetically engineered: combined parts of DNA from different plants to produce a new plant

Excerpt from “How We Made the First Flight”

by Orville Wright

In 1903 brothers Wilbur and Orville Wright conducted experiments related to flying machines. These experiments would eventually lead to air travel becoming a reliable form of transportation.

During the night of December 16, 1903, a strong cold wind blew from the north. When we arose on the morning of the 17th, the puddles of water, which had been standing about camp since the recent rains, were covered with ice. The wind had a velocity of 10 to 12 meters per second (22 to 27 miles an hour). We thought it would die down before long, and so remained indoors the early part of the morning. But when ten o’clock arrived, and the wind was as brisk as ever, we decided that we had better get the machine out and attempt a flight. We hung out the signal for the men of the Life Saving Station.¹ We thought that by facing the flyer into a strong wind, there ought to be no trouble in launching it from the level ground about camp. We realized the difficulties of flying in so high a wind, but estimated that the added dangers in flight would be partly compensated for by the slower speed in landing.

Final Preparations

We laid the track on a smooth stretch of ground about one hundred feet north of the new building. The biting cold wind made work difficult, and we had to warm up frequently in our living room, where we had a good fire in an improvised stove made of a large carbide² can. By the time all was ready, J. T. Daniels, W. S. Dough and A. D. Etheridge, members of the Kill Devil³ Life Saving Station; W. C. Brinkley of Manteo, and Johnny Moore, a boy from Nags Head,⁴ had arrived.

We had a “Richard” hand anemometer with which we measured the velocity of the wind. Measurements made just before starting the first flight showed velocities of 11 to 12 meters per second, or 24 to 27 miles per hour. . . .

Audacity—and Calculation

Wilbur having used his turn in the unsuccessful attempt on the 14th, the right to the first trial now belonged to me. After running the motor a few minutes to heat it up, I released the wire that held the machine to the track, and the machine started forward in the wind. Wilbur ran at the side of the machine, holding the wing to balance it on the track. Unlike the start on the 14th, made in a calm, the machine, facing a 27-mile wind, started very slowly. Wilbur was able to stay with it till it lifted from the track after a forty-foot run. One of the Life Saving men snapped the camera for us, taking a picture just as the machine had reached the end of the track and had risen to a height of about two feet. The slow forward speed of the machine over the ground is clearly shown in the picture by Wilbur’s attitude. He stayed along beside the machine without any effort.

Flight

The course of the flight up and down was exceedingly erratic, partly due to the irregularity of the air, and partly to lack of experience in handling this machine. The control of the front rudder was difficult on account of its being balanced too near the center. This gave it a tendency to turn itself when started; so that it turned too far on one side and then too far on the other. As a result the machine would rise suddenly to about ten feet, and then as suddenly dart for the ground. A sudden dart when a little over a hundred feet from the end of the track, or a little over 120 feet from the point at which it rose into the air, ended the flight. As the velocity of the wind was over 35 feet per second and the speed of the machine over the ground against this wind ten feet per second, the speed of the machine relative to the air was over 45 feet per second, and the length of the flight was equivalent to a flight of 540 feet made in calm air. This flight lasted only 12 seconds, but it was nevertheless the first in the history of the world in which a machine carrying a man had raised itself by its own power into the air in full flight, had sailed forward without reduction of speed and had finally landed at a point as high as that from which it started.

From “How We Made the First Flight” by Orville Wright—Public Domain/Federal Aviation Administration

¹Life Saving Station: one of the rescue stations along the Atlantic coastline that provided assistance to mariners in distress

²carbide: a very hard material composed of carbon and other heavy metals

³Kill Devil: the town of Kill Devil Hills in eastern North Carolina

⁴Nags Head: a town in eastern North Carolina

Excerpt from “How Exercise Could Help You Learn a New Language”

by Gretchen Reynolds

Many scientists suspect that exercise alters the biology of the brain in ways that make it more malleable and receptive to new information, a process that scientists refer to as plasticity.

But many questions have remained unanswered about movement and learning, including whether exercise is most beneficial before, during or after instruction and how much and what types of exercise might be best.

So for a new study, which was published recently in PLOS One, researchers in China and Italy decided to home in on language learning and the adult brain.

Language learning is interesting. As young children, almost all of us picked up our first language easily. We didn’t have to be formally taught; we simply absorbed words and concepts.

But by early adulthood, the brain generally begins to lose some of its innate language capability. It displays less plasticity in areas of the brain related to language. As a result, for most of us, it becomes harder to learn a second language after childhood.

To see what effects exercise might have on this process, the researchers first recruited 40 college-age Chinese men and women who were trying to learn English. The students had some facility with this second language but were far from proficient.

The researchers then divided the students into two groups. Those in one group would continue to learn English as they had before, primarily while seated in rote vocabulary-memorization sessions.

The others would supplement these sessions with exercise.

Specifically, the students would ride exercise bikes at a gentle pace (about 60 percent of their maximum aerobic capacity) beginning 20 minutes before the start of the lessons and continuing throughout the 15 minutes or so of instruction.

Both groups learned their new vocabulary by watching words projected onto large screens, together with comparable pictures, such as “apple” and a Red Delicious. They were shown 40 words per session, with the sequence repeated several times.

Afterward, the students all rested briefly and then completed a vocabulary quiz, using computer keys to note as quickly as possible whether a word was with its correct picture. They also responded to sentences using the new words, marking whether the sentences were accurate or, in the case of “The apple is a dentist,” nonsensical. Most linguists¹ feel that understanding sentences shows greater mastery of a new language than does simple vocabulary improvement.

The students completed eight vocabulary sessions over the course of two months.

And at the end of each lesson, the students who had ridden bikes performed better on the subsequent vocabulary tests than did the students who sat still.

They also became more proficient at recognizing proper sentences than the sedentary students, although that difference did not emerge until after several weeks of instruction.

Perhaps most interesting, the gains in vocabulary and comprehension lingered longest for the cyclists. When the researchers asked the students to return to the lab for a final round of testing a month after the lessons—without practicing in the meantime—the cyclists remembered words and understood them in sentences more accurately than did the students who had not moved.

“The results suggest that physical activity during learning improves that learning,” says Simone Sulpizio, a professor of psychology and linguistics at the University Vita-Salute San Raffaele in Milan, Italy, and a study co-author.

These improvements extend beyond simply aiding in memorization, she added. The exercise also deepened language learners’ grasp of how to use their newly acquired words.

This study involved college students performing relatively light exercise, though, and cannot tell us whether other people completing other types of exercise would achieve the same results.

It also offers no clues about what is occurring inside the brain that might be contributing to the benefits of the exercise. But many past studies have shown that exercise prompts the release of multiple neurochemicals in the brain that increase the number of new brain cells and the connections between neurons, Dr. Sulpizio says. These effects improve the brain’s plasticity and augment the ability to learn.

From a real-world standpoint, the study’s implications might seem at first to be impractical. Few classrooms are equipped with stationary bicycles. But specialized equipment is probably unnecessary, Dr. Sulpizio says.

“We are not suggesting that schools or teachers buy lots of bicycles,” she says. “A simpler take-home message may be that instruction should be flanked by physical activity.”

From “How Exercise Could Help You Learn a New Language” by Gretchen Reynolds from THE NEW YORK TIMES, August 16, 2017. Copyright © 2017 The New York Times Company.

¹linguists: scientists who study language

Excerpt from “Research Riddle Resolved”

For centuries, scientists were confounded by an animal that seemed to look and act like a combination of a bird, a reptile, and a mammal. It has a bill like a duck and lays eggs but produces milk for its young. It lives in a burrow, has fur, and can make venom. We now know that this animal is called a duck-billed platypus. A platypus is a monotreme, a type of egg-laying mammal.

Hundreds of years after the first sightings of the platypus, the animal still captures our imagination anew and irresistibly attracts the attention of science writers everywhere. The May 2008 Nature report detailing the DNA insides of the duck-billed platypus invited colorful tales from just about every mainstream media outlet.

But cuteness and weirdness aside, the platypus research results are a gold mine for medical researchers. The findings cement what may have seemed totally obvious but turned out to be a bit of a scientific surprise: platypus DNA is a patchwork of genes from reptiles, birds, and mammals.

Evolution Fusion

In other words, the platypus heritage is laid out in an evolutionary DNA tapestry that marks the time, hundreds of millions of years ago, when reptiles and mammals branched off the evolutionary tree.

So what? The platypus is nothing like a human, so what can its DNA tell us about people and the diseases we get?

Plenty, says an international team of scientists who did this work.

The platypus genome results are far more than confirmation of a scientific oddity. They provide researchers a window into a time in history when mammals became unique—gaining the ability to bear live young, produce milk for them, and grow a warm, furry coat.

That’s important because our own, modern-day genomes are still a big mystery and researchers need much more information to be able to translate our genetic language into useful health knowledge.

One of the ways scientists can decipher meaning from within our 3 billion DNA “letters,” or nucleotides, is to compare human genes with those from animals, to see what has been kept the same and what has evolved to be different. . . .

Same and Different

In an approach called comparative genomics, scientists compare the genome sequences of several species: human, mouse, and a wide variety of other organisms from single-celled fungi to elephants and, now, the platypus.

The goal of this research is to find regions of similarity and difference in order to better understand the structure and function of human genes.

Comparative genomics is directly related to evolution because all living things share a common ancestor. By using computer tools to examine genes that have been kept the same in many organisms over millions of years, researchers can locate signals that control how genes work. This information may translate into ways to understand, treat, and prevent human diseases. . . .

Chicken or Egg?

When researchers analyzed platypus DNA and compared it to that of chickens, snakes, and lizards, the findings traced the evolutionary path from birds and reptiles to mammals. They learned that the platypus lost most of its genetic ability to produce egg yolk—as compared to chicken genes. This suggests its departure from “chicken-ness.”

But, through evolutionary change, the platypus gained the ability to make milk that is rich in nutrients. Platypuses have genes that make the milk protein casein: just like we do.

A male platypus can, like its ancestral snake and lizard cousins, produce venom. The platypus ejects this venom through special glands in its back legs. The evolutionary reason for maintaining such molecular weaponry isn’t yet clear, but what is fascinating is that it appears nature mixed and matched together DNA pieces separately to create the venom genes in reptiles and monotremes like the platypus.

The scientific value of pinning genetics to physiological function—like milk production—is high. Such investigations may help medical researchers understand health issues related to reproduction and lactation. Although lactation is an ancient reproductive trait, mammals—including the platypus—are unique in their ability to produce milk that is extraordinarily nutritious, containing a rich blend of sugars, fats, and proteins.

More generally, though, studying how nature cuts and pastes gene modules gives scientists an inside scoop on how genetic changes relate to health and disease risk.

One thing is clear—the stunning blend of reptile, bird, and mammal puts the platypus in a class of its own, and it gives researchers much more: information about how mammals like us came about.

[Scientists’] genetic sleuthing of platypuses, chimps, fish, sunflowers—you name it—continues to teach scientists how millions of years of evolution progressed. This provides vital information to understanding the role of genes in the health and disease of mammals like us and our pets, and can also help preserve our rich and diverse planet.

From “Research Riddle Resolved”—Public Domain/National Institutes of Health

Is It Time for Term Limits?

In 1799, when George Washington’s supporters asked him to consider serving a third term as president of the United States, he declared, “Prudence on my part must arrest any attempt at the well meant, but mistaken views of my friends, to introduce me again into the Chair of Government.” Even though some of his contemporaries advocated for a lifetime appointment for presidents, Washington thought that government officials should not seek to gain unfair power. Only one president has been elected to four terms: Franklin Delano Roosevelt. He was elected to a third term in 1940 and a fourth in 1944 due to the challenges of the Great Depression and World War II. This departure from the rule worried some, and on March 21, 1947, Congress passed the Twenty-Second Amendment to the Constitution, legally limiting the office of president to two four-year terms.

Presidential terms are clearly limited in the Constitution, but for people serving in Congress, this is not the case. Currently, members of the House of Representatives, who serve two-year terms, and Senators, who serve six-year terms, can run for reelection an unlimited number of times. Because of the possibility of unlimited reelections, many people are beginning to believe that limiting congressional terms would benefit our government. Modern surveys conducted by multiple firms consistently show that American citizens of a variety of backgrounds and political leanings approve of the idea of setting term limits for members of Congress.

American citizens are not the only supporters of term limits for Congress. Even some members of Congress themselves have spoken out in support of this change. Former Senator Joe Lieberman, upon his retirement, suggested that Congress “might be healthier and less partisan¹ and less rigid if it turned over more often, and term limits are one way to do that.” Michael Olson and Jon Rogowski state in their article “Legislative Term Limits and Polarization” that “proponents of term limits argue that limiting the number of terms legislators can serve in office would reduce the level of partisan conflict, encourage compromise and cooperation, and improve the quality of representation.”

Experienced politicians certainly can build on years of knowledge, but term limit supporters point out that career politicians may base key decisions on their own personal long-term goals. In the article “Term Limitations and the Myth of the Citizen-Legislator,” author Elizabeth Garrett states that “under term limits, a careerist needs to move up the political opportunity structure to remain in elected office, but the probability of unimpeded upward movement decreases as the number of available positions that are perceived as advancements decline.”

While challenging the career politician’s path is seen as a benefit to term limit supporters, there is a possibility that a Congress mostly composed of newcomers could severely affect policy making. Experienced politicians have a deep knowledge of congressional processes, and in addition, politicians who have served together for extended periods have a chance to develop trusting relationships, even across party lines. Molly Reynolds, a congressional expert for the Brookings Institution, says that members who are restricted by term limits “have neither the time nor the incentive to develop the relevant expertise they need to be good at their jobs. If members don’t have that expertise themselves, they’re more likely to rely on outsiders, including lobbyists, to replace that expertise.”

In fact, first-time politicians’ susceptibilities to lobbyists, or groups seeking to influence legislators, have actually been put to the test on the state level. In 2006, the National Conference of State Legislatures Study revealed that term limits may increase the influence of lobbyists. In the 1990s, more than twenty states implemented term limits within their state governments. The inexperienced state lawmakers began depending on special-interest groups for their expertise on issues. In the end, many people believed that implementing term limits in the state legislature caused problems, and since then, six states have repealed the limits.

Additionally, those who oppose term limits maintain that the turnover rate in Congress is sufficient. Thomas E. Mann, Senior Fellow in governance studies at the Brookings Institution, notes that every decade, new members replace at least half the members of the House and the Senate, due to retirement or elections. Still, the average length of time in office has mushroomed. For example, the 65th Congress (1917–1919) had an average service time of 5.3 years for members of the House of Representatives and 5.7 years for Senate members. The 114th Congress (2015–2017) had an average of 8.8 years for members of the House and 9.7 years for senators.

Should Congress pass a constitutional amendment to institute congressional term limits? Perhaps one day people will have a chance to vote on the issue.

PERCENTAGE OF REPRESENTATIVES AND SENATORS REELECTED

House of Representatives Total seats: 435	Year	Percentage Reelected
	1950	83.2
	1978	82.3
	1998	90.8
	2016	87.4

Senate Total seats: 100	Year	Percentage Reelected
	1950	68.8
	1978	60.0
	1998	89.7
	2016	93.1

¹partisan: showing a strong and sometimes blind adherence to a particular political party

An Early Warning

One of the books that has done the most to alert the world to the dangers of environmental degradation is George Perkins Marsh’s Man and Nature. Its message—that Western society is in the process of causing irreparable harm to the environment—greatly influenced ecologists during the beginning of the modern environmentalist movement in the 1960s. Marsh was not, however, part of this movement. Surprisingly, Man and Nature was first published in 1864.

Marsh first observed the environmentally destructive effects of human activities while growing up in Vermont in the early nineteenth century. The heavy demand for firewood had depleted the forests, and extensive sheep grazing had stripped the land. The result was flooding and soil erosion. Furthermore, streams were fouled by wastes dumped from numerous mills and dye houses.

Much later in his life, after careers in law, business, farming, and politics, Marsh served as ambassador to Italy. There he noticed land abuse similar to what he had seen in Vermont. Overgrazing and forest mismanagement had rendered areas that had been productive farmland since the days of the Roman Empire desolate. Marsh attributed this to what he called “man’s ignorant disregard for the laws of nature.”

In Italy, Marsh began to organize his observations and theories. He wrote in a way intended to educate readers about the impact of industrial and agricultural practices on the environment. In Man and Nature, he evaluated the important relationships between animals and plants, discussed forestry practices in great detail, and analyzed the ways natural water supplies are affected by human use.

Man and Nature challenged the popular belief that nature can heal any damage that people inflict upon it. Marsh argued that people may use and enjoy, but not destroy, the riches of the earth.

Furthermore, he asserted that everything in nature is significant and that even the tiniest organism affects the fragile environmental balance. His belief that drastic alteration of this balance would be dangerous is now accepted as a fundamental principle of modern environmental science.

Although he pointed out environmental damage caused by irresponsible human activities, Marsh did not oppose every human alteration to the environment. To him, the goal was proper management, not a return to wilderness conditions. People should consider the consequences of their actions, he wrote, and become “co-worker[s] with nature.” Marsh praised the Suez Canal, the human-made waterway between the Mediterranean Sea and the Gulf of Aden, as “the greatest and most truly cosmopolite physical improvement ever undertaken by man.” He believed that the advantages of the canal— improved transportation and commerce—would outweigh any environmental damage. Yet he also warned of possible unintended consequences, such as destructive plants and animals spreading from one body of water to the other.

Marsh was considered a radical thinker during his lifetime. By the late nineteenth century, however, his writings, along with those of John Muir, Henry David Thoreau, and others, had inspired what became known as the conservation movement. The conservationists of that time sought to educate the public that wilderness areas were worth preserving and were responsible for creating the National Park Service and the National Forest Service.

Ruins of a Fabled City

The African country of Zimbabwe took its name from the Shona word meaning “stone enclosures” or “venerated houses.” In fact, today dozens of stone ruins are scattered throughout Zimbabwe and other areas in southeastern Africa. One of these ruins, known as Great Zimbabwe, was once a fabled city that inspired tales that circulated throughout Europe. Where was this remarkable city, and who had built it? For centuries the mystery occupied the minds of explorers and treasure seekers.

The first reports to Europeans of Great Zimbabwe were spread a thousand years ago by Arab traders sailing between the Middle East and the east coast of Africa. The traders told of the fabulous wealth of a mysterious stone city in the African interior. In the trader’s tales, that city became associated with the Europeans’ understanding of Middle Eastern history—the Queen of Sheba, King Solomon and his legendary gold mines, long since lost to the world. By the sixteenth century, Portuguese explorers regularly visited East Africa, searching for King Solomon’s gold, but they never found Great Zimbabwe. In 1552, a Portuguese historian, João de Barros, recorded a story told by Arabs about a city with a “square fortress of masonry within and without, built of stones of marvelous size, and there appears to be no mortar joining them.”

In fact, Great Zimbabwe was a marvel. In one area a massive wall more than thirty feet high and twenty feet thick created a great enclosure. Another area contained a fortress-like series of walls, corridors, and steps built into the bluff that overlooks the ruins. Throughout the city, each stone was precisely fitted to the others without the use of mortar.

In the 1870s Karl Mauch, a German geologist, was the first European to see Great Zimbabwe, by then in ruins. Mauch realized that he had “rediscovered” the fabled city from de Barros’s story. He jumped to the conclusion that Great Zimbabwe had been built by the Queen of Sheba. British authorities sent a British journalist, Richard Hall, to Great Zimbabwe to investigate Mauch’s report. Archaeology was still in its infancy, and Hall, convinced that the structures had been built by ancient people from the Middle East, dug up and discarded archaeological deposits that would have revealed much about the true history of Great Zimbabwe. Later European excavations destroyed even more valuable evidence.

In the twentieth century, after excavating areas that had not been disturbed, David Randall-MacIver, a Scottish Egyptologist, and Gertrude Caton-Thompson, an English archaeologist, concluded that the ruins were unmistakably African in origin. Great Zimbabwe was most likely built during the fourteenth or fifteenth century by the ancestors of the present-day Shona people. Recent carbon-14 dating supports their conclusion. Great Zimbabwe was once home to an estimated 20,000 people, the center of a great Shona kingdom. Wealthy Shona kings traded their ivory and gold in coastal towns for other goods, thus accounting for the discovery of beads and other foreign wares in the ruins.

One mystery of Great Zimbabwe had been solved. Another mystery remains: why was the settlement at Great Zimbabwe abandoned, leaving the magnificent stone architecture to fall into ruins?

The Year without a Summer

The eruption of the Philippine volcano Mount Pinatubo in June 1991 sent a huge cloud of gas and dust encircling the globe. The dust and ash from Mount Pinatubo was blamed for a two-year decrease in global temperature, changes in weather patterns, and damage to the ozone layer. The situation brings to mind a time now remembered as “The Year without a Summer,” a meteorological event that occurred 175 years earlier. At that time, harsh weather conditions plagued much of eastern North America and, to a lesser extent, northern Europe.

April 1816 brought typical spring weather to upstate New York and New England; trees budded, and farmers prepared to plow and plant. In May, however, the expected warm temperatures failed to arrive. Most people remained optimistic, waiting for the summer that was “just around the corner.” They waited in vain. During the first week of June, ten inches of snow fell on New England. Throughout the month, temperatures rarely rose above the 30s. Many farmers replanted crops several times, only to see them stunted or destroyed by sleet, hail, and icy winds. July and August brought little improvement. During most days the temperature stayed in the 40s. Farmers’ diaries document the farmers’ daily struggles with near-freezing temperatures, failing crops, and dying farm animals. The few crops that managed to survive were killed by frost in mid-September. Winter came early in New England and was unusually severe. Even the South was affected; on July 4, the high temperature for Savannah, Georgia, was only 46 degrees Fahrenheit!

Some religious leaders warned their congregations that the unusual weather meant that the end of the world was drawing near. Other leaders attributed the cool weather to unusual sunspot activity. The proliferation of the newly invented lightning rod was also blamed as some people believed that lightning rods had interrupted the natural temperature balance of Earth, causing the cooler temperatures.

It was not until October that the first plausible explanation for “The Year without a Summer” was suggested. Friedrich Bessel, a German astronomer, reported seeing thick clouds of dust in the upper atmosphere. He theorized that these dust particles screened portions of Earth from the warming rays of the sun. It was discovered that in April 1815, Mount Tambora, an Indonesian volcano, had erupted with such force that it had sent an estimated 100 cubic miles of fine dust into the atmosphere. Witnesses to the eruption reported that the sky remained dark for two days. The dust then rose high into the stratosphere, where it encircled the world for several years to come.

Skeptics in 1816 doubted that a faraway volcano could steal their summer. However, most present-day researchers believe Bessel’s explanation to be generally correct, demonstrating the global nature of weather. The dust in the atmosphere eventually settled, and the spring of 1817 was back to normal.

The Tunguska Fireball

On June 30, 1908, an enormous fireball shot across the sky and exploded high above the remote Tunguska River Valley in the Siberian region of Russia. Twenty miles away, huts were flattened and people were flung into the air. Villagers 40 miles away felt the heat and heard explosions, and tremors were recorded at a German seismic station more than 3,000 miles away.

What caused the intense light and the horrendous destruction of the Tunguska Fireball, as it came to be called? Scientists and laypeople have debated the question for over 100 years. Not until 1927 did a scientific expedition, led by Russian scientist Leonid Kulik, reach the remote site. Kulik discovered a vast region of scorched and downed trees, their trunks pointing away from the center of the blast. Convinced that a meteorite was responsible, Kulik searched for evidence—a crater, a buried meteorite, even fragments of the exploded mass. He never found it.

Other scientists, amateur astronomers, and the public suggested alternative theories of what had happened. Some thought it was an earthquake. Perhaps, others said, a black hole—a theoretical object in space where gravity is so strong that even light cannot get out—had collided with Earth or an alien spaceship carrying nuclear material had crashed.

For many years Russian scientists believed that the Tunguska Fireball was a comet—a cluster of dust and frozen gases—that had exploded a few hundred feet above the ground. They pointed to the lack of meteoric evidence and the June 30 date, a time of year when Earth was passing through cometary debris. Other scientists disagreed, arguing that a comet would have burned quickly in Earth’s atmosphere and could not have created such a blast.

Many Western scientists believed that a meteorite was responsible, despite the lack of evidence. The pattern of fallen trees suggested that they were knocked down by a blast about 4 miles above the ground with an energy of 15 megatons of TNT, consistent with a meteoric blast. Yet repeated searches of the surrounding forest and wetlands revealed no evidence of a meteorite.

During the 1990s an Italian physicist named Menotti Galli became interested. Galli had previously investigated whether particles from outer space can add carbon atoms to the cellulose in trees. Perhaps the trees at the Tunguska site hid evidence of such extraterrestrial material. Galli and his colleagues traveled to the site by helicopter to gather core samples from spruce trees that had lived through the blast. They analyzed the particles trapped in the trees’ resin, and the results were remarkable. Based on studying the trees’ rings during the time period when the Tunguska Fireball occurred, the researchers found that the resin contained high levels of high-proton elements, such as copper, gold, and nickel. In fact, it contained ten times more such particles than resin dating from either before or after that time period. Some previously discovered meteorites had also contained elevated levels of these elements, suggesting that the particles had an extra-earthly origin. But then where is the crater? Is it nearby Lake Cheko, as some claim? Or was the meteorite reduced to dust in the atmosphere? Can scientists rule out a comet carrying those elements? The mystery remains unsolved.

Uncovering the Past

Archaeology as a distinct branch of science is only about two centuries old. The first archaeological activities focused largely on the search for clues about earlier human societies. In the nineteenth century, most archaeologists were amateurs trained in ancient languages and history. Many were art historians whose interest lay in the artwork and monuments of ancient civilizations. For the most part, their excavations were aimed at uncovering and removing priceless artwork and other valuable artifacts for museum display. Collectively, these early archaeologists are now considered traditional archaeologists.

Today, however, there is a different approach to archaeology, one that tries to reconstruct the everyday life of people in ancient times by applying the scientific methods of a range of specialized fields. Modern archaeologists take full advantage of available technology. Laptop computers enable digging teams to record their finds at each level of an excavation. With sketchpad computer software, archaeologists can draw their finds in the field. Three-dimensional computer modeling enables researchers to create floor plans and elevations for the structures they uncover. Archaeologists can also use remote sensing technologies such as radar and lidar, which is similar to radar but it uses laser light instead of radio waves. These technologies enable scientists to detect traces of early settlements that are not visible to the human eye.

The excavations at Kourion, a Roman port city on the island of Cyprus in the Mediterranean Sea, serve as an example of the modern approach. Portions of Kourion had been unexpectedly buried by a massive earthquake in the fourth century A.D. Traditional archaeologists were interested primarily in the remains of Kourion’s theater, temple, and classical monuments. They also collected precious objects, such as jewelry, found in nearby tombs. Modern archaeologists, however, have focused their studies and excavations on the settlement itself. This preserved seaport has proved to be a gold mine of important information about everyday life sixteen centuries ago.

During one excavation of a house at Kourion, for example, forensic anthropologists were able to reconstruct the skeleton of a young girl, whom they called Camelia. On the basis of her teeth, they determined her age to be about thirteen, although measurement of her skeleton showed that she was only the size of a modern eleven-year-old. The study of the teeth also confirmed her sex and pointed to her excellent health; Camelia had no cavities. Even after centuries, the forensic scientists could study the physical evidence in ways similar to those used in criminal investigations to determine the circumstances of Camelia’s death.

Other specialists on this excavation included a zooarchaeologist, who identified animal remains, including the skeleton of a mule found near Camelia. Another specialist, a paleobotanist, studied the contents of a bake oven at the site and identified four domesticated grains among the charred crumbs—evidence of a kind of ancient multigrain bread.

Although the archaeologists at this site unearthed a few beautiful items, the excavation did not uncover any priceless artwork for museums. Nonetheless, the archaeological processes used in Kourion have given us a valuable insight into everyday life in a Roman city.