Ice Ages

“Earth’s past includes periods of radically different climate-ice ages”

  • Who Discovered it?: Louis Agassiz.
  • Year of the Discovery: 1837

How was it Discovered?


It was a revolutionary idea: Earth’s climate had not always been the same. Every scientist for thousands of years had assumed that Earth’s climate had remained unchanging for all time. Then Louis Agassiz discovered proof that all Europe had once been covered by crushing glaciers. Earth’s climate had not always been as it was now. With that discovery, Agassiz established the concept of an ever-changing Earth.

Louis Agassiz thought of himself as a field geologist more than as a college professor. During weeks of rambling hikes through his native Swiss Alps in the late 1820s, he noticed several physical features around the front faces of Swiss valley glaciers. First, glaciers wormed their way down valleys that were “U” shaped—with flat valley bottoms. River valleys were always “V” shaped. At first, he thought that glaciers naturally formed in such valleys. Soon he realized that the glaciers, themselves, carved valleys in this characteristic “U” shape.

Next, he noticed horizontal gouges and scratches in the rock walls of these glacier valleys—often a mile or more in front of the actual glacier. Finally, he became aware that many
of these valleys featured large boulders and rock piles resting in the lower end of the valley where no known force or process could have deposited them.

Soon Agassiz realized that the mountain glaciers he studied must have been much bigger and longer in the past and that they, in some distant past, had gouged out the valleys, carried the rocks that scored the valleys’ rock walls leaving claw-mark scratches, and deposited giant boulders at their ancient heads.

In the early 1830s, Agassiz toured England and the northern European lowlands. Here, too, he found “U”-shaped valleys, horizontal gouges, and scratch marks in valley rock walls and giant boulders mysteriously perched in the lower valley reaches.

It looked like the signature of glaciers he had come to know from his Swiss studies. But there were no glaciers for hundreds of miles in any direction. By 1835, the awe inspiring truth hit him. In some past age, all Europe must have been covered by giant glaciers. The past must have been radically different than the present. Climate was not always the same.

In order to claim such a revolutionary idea, he had to prove it. Agassiz and several hired assistants spent two years surveying Alpine glaciers and documenting the presence of the tell tale signs of past glaciers.

When Agassiz released his findings in 1837, geologists world wide were awed. Never before had a researcher gathered such extensive and detailed field data to support a new theory. Because of the quality of his field data, Agassiz’s conclusions were immediately accepted—even though they radically changed all existing theories of Earth’s past.

Agassiz created a vivid picture of ice ages and proved that they had existed. But it was Yugoslavian physicist Milutin Milankovich, in 1920, who explained why they happened.

Milankovich showed that Earth’s orbit is neither circular, nor does it remain the same year after year and century after century. He proved that Earth’s orbit os cil lates be tween being more elongated and being more circular on a 40,000-year cycle. When its orbit pulled the earth a little farther away from the sun in winter, ice ages happened. NASA scientists confirmed this theory with research conducted between 2003 and 2005.

Fun Facts: During the last ice age the North American glacier spread south to where St. Louis now sits and was over a mile thick over Minnesota and the Dakotas. So much ice was locked into these vast glaciers that sea level was almost 500 feet lower than it is to day.

Order in Nature

All living plants and animals can be grouped and organized into a simple hierarchy.

  • Who Discovered it?: Carl Linnaeus
  • Year of Discovery: 1735

How was it Discovered?

Carl Linnaeus hated disorder. He claimed he could never understand anything that was not systematically ordered. Born in Sweden in 1707, he was supposed to become a priest like his father. But Carl showed little aptitude for, and no interest in, the priesthood and was finally allowed to switch to medicine.

He entered the University of Lund’s School of Medicine in 1727 but spent more time in the university’s small botanical garden than in class. Linnaeus had been fascinated by plants and flowers since he was a small child. In 1728 Linnaeus transferred to the University of Uppsala (partly because they had bigger botanical gardens). There he read a paper by French botanist Sebastian Vaillant that claimed (it was considered shockingly revolutionary at the time) that plants reproduced sexually and had male and female parts that corresponded to the sexual organs of animals.

The idea appealed to Linnaeus. As an obsessive cataloger, he had always detested the notion that each of the thousands of plants he saw in botanical gardens was individual and separate species. Linnaeus began to wonder if he could use the differences in plants’ reproductive parts as a means of classifying and ordering the vast array and profusion of plants. His dream of bringing order to the chaos of nature was born.

Glib, cordial, and with a natural talent for ingratiating himself with rich and powerful supporters, Linnaeus was able to arrange financial support for a series of expeditions across different areas of Sweden to study and catalog plant species. He spent months tramping across the countryside listing, describing, and studying every plant he found. His expeditions were always the picture of perfect order. He started each day’s hike precisely at 7:00 in the morning. Linnaeus stopped for a meal break at 2:00 P.M. He paused for a rest and lecture break at 4:00 P.M.

During these expeditions, Linnaeus focused his studies on the reproductive systems of each plant he found. Soon he discovered common characteristics of male and female plant parts in many species that he could group into a single category. He lumped these categories together into larger groups that were, again, combined with other groups into yet larger classifications. He found that plants fit neatly into groups based on a few key traits and that order did exist in the natural world.

By 1735 he had described more than 4,000 species of plants and published his classification system in a book, Systema Naturae. This system described the eight levels Linnaeus finally built into his system: species, genus, family, order, Class, Subphylum, Phylum, and Kingdom. This system—based solely on the sexual elements of plants and (later) animals—was controversial with the public. But botanists found it easy to use and appealing.

Linnaeus’s system spread quickly across Europe and was often drawn as a tree, with giant branches being classes, down to the tiniest twigs of species. From these drawings came the concept of a “Tree of Life.”

Linnaeus spent the next 30 years touring Europe adding new plants to his system. In 1740 he added animal species into his system. By 1758 he had described and classified 4,400 animal species and more than 7,700 plant species.

In 1758, with the tenth edition of his book, he introduced the binomial (two-name) system of naming each plant and animal by species and genus. With that addition, Linnaeus’s system was complete. He had discovered both that order existed in the natural world and a system for describing that order—a system still very much alive and in use today.


Fun Facts: The world’s most massive living tree is General Sherman, the giant sequoia (Sequoiadendron giganteum) growing in the Sequoia National Park in California. It stands 83.82m (274.9 ft.) tall and has a diameter of 11.1 m (36 ft., 5 in.). This one tree is estimated to contain enough wood to make five billion matches—one for almost every person on Earth.



An atom is the smallest particle that can exist of any chemical element.

  • Who discovered it?: John Dalton
  • Year of Discovery: 1802

How was it Discovered?


In the fifth century B.C.Leucippus of Miletus and Democritus of Abdera theorized that each form of matter could be broken into smaller and smaller pieces. They called that smallest particle that could no longer be broken into smaller pieces an atomGalileo and Newton both used the term atom in the same general way. Robert Boyle and Antoine Lavoisier were the first to use the word element to describe one of the newly discovered chemical substances. All of this work, however, was based on general philosophical theory, not on scientific observation and evidence.

John Dalton was born in 1766 near Manchester, England, and received a strict Quaker upbringing. With little formal education, he spent 20 years studying meteorology and teaching at religious, college-level schools. Near the end of this period, Dalton joined and presented a variety of papers to the Philosophical Society. These included papers on the barometer, the thermometer, the hygrometer, rainfall, the formation of clouds, evaporation, atmospheric moisture, and dewpoint. Each paper presented new theories and advanced research results.

Dalton quickly became famous for his innovative thinking and shifted to science research full time. In 1801 he turned his attention from the study of atmospheric gasses to chemical combinations. Dalton had no experience or training in chemistry. Still, he ploughed confidently into his studies.

By this time almost 50 chemical elements had been discovered—metals, gasses, and nonmetals. But scientists studying chemistry were blocked by a fundamental question they couldn’t answer: How did elements actually combine to form the thousands of compounds that could be found on Earth? For example, how did hydrogen (a gas) combine with oxygen (another gas) to form water (a liquid)? Further, why did exactly one gram of hydrogen always combine with exactly eight grams of oxygen to make water—never more, never less?

Dalton studied all of the chemical reactions he could find (or create), trying to develop a general theory for how the fundamental particle of each element behaved. He compared the weights of each chemical and the likely atomic structure of each element in each compound. After a year of study, Dalton decided that these compounds were defined by simple numerical ratios by weight. This decision allowed him to deduce the number of particles of each element in various well-known compounds (water, ether, etc.).

Dalton theorized that each element consisted of tiny, indestructible particles that were what combined with other elements to form compounds. He used the old Greek word, atom, for these particles. But now it had a specific chemical meaning.

Dalton showed that all atoms of any one element were identical so that any of them could combine with the atoms of some other element to form the known chemical compounds. Each compound had to have a fixed number of atoms of each element. Those fixed ratios never changed. He deduced that compounds would be made of the minimum number possible of atoms of each element. Thus water wouldn’t be H4O2 because H2O was simpler and had the same ratio of hydrogen and oxygen atoms.

Dalton was the first to use letter symbols (H, O, etc.) to represent the various elements. Scientists readily accepted Dalton’s theories and discoveries, and his concepts quickly spread across all Western science. We still use his concept of an atom today.

“Since atoms are the key to understanding chemistry and physics, Dalton’s discovery of the atom ranks as one of the greatest turning points in science. Because of this discovery, Dalton is often called the father of modern physical science.”


Plants use sunlight to convert carbon dioxide in the air into new plant matter.

  • Who discovered it?: Jan Ingenhousz
  • Year of Discovery: 1779


How was it discovered?

Photosynthesis is the process that drives plant production all across Earth. It is also the process that produces most of the oxygen that exists in our atmosphere for us to breathe. Plants and the process of photosynthesis are key elements in the critical (for humans and other mammals) planetary oxygen cycle.

When Jan Ingenhousz discovered the process of photosynthesis, he vastly improved our basic understanding of how plants function on this planet and helped science gain a better understanding of two important atmospheric gases: oxygen and carbon dioxide. 

Modern plant engineering and crop sciences owe their foundation to Jan Ingenhousz’s discovery.

Jan Ingenhousz was born in Breda in the Netherlands in 1730. He was educated as a physician and settled down to start his medical practice back home in Breda.

In 1774 Joseph Priestley discovered oxygen and experimented with this new, invisible gas. In one of these tests, Priestley inserted a lit candle into a jar of pure oxygen and let it burn until all oxygen had been consumed and the flame went out. Without allowing any new air to enter the jar, Priestley placed mint sprigs floating in a glass of water in the jar to see if the mint would die in this “bad” air. But the mint thrived. After two months, Priestley placed a mouse in the jar. It also lived proving that the mint plant had restored oxygen to the jar’s air. But this experiment didn’t always work. Priestley admitted that it was a mystery and then moved on to other studies.

In 1777, Ingenhousz read about Priestley’s experiments and was fascinated. He could focus on nothing else and decided to investigate and explain Priestley’s mystery. Over the next two years, Ingenhousz conducted 500 experiments trying to account for every variable and every possible contingency. He devised two ways to trap the gas that a plant produced. One was to enclose the plant in a sealed chamber. The other was to submerge the plant.

Ingenhousz used both systems but found it easier to collect and study the gas collected under water as tiny bubbles. Every time he collected the gas that a plant gave off, he tested it to see if it would support a flame (have oxygen) or if it would extinguish a flame (be carbon dioxide).

Ingenhousz was amazed at the beauty and symmetry of what he discovered. Humans inhaled oxygen and exhaled carbon dioxide. Plants did just the opposite sort of. Plants in sunlight absorbed human waste carbon dioxide and produced fresh oxygen for us to breathe. Plants in deep shade or at night (in the dark), however, did just the opposite. They acted like humans, absorbing oxygen and producing carbon dioxide.

After hundreds of tests, Ingenhousz determined that plants produced far more oxygen than they absorbed. Plants immersed in water produced a steady stream of tiny oxygen bubbles when in direct sunlight. Bubble production stopped at night. Plants left for extended periods in the dark gave off a gas that extinguished a flame. When he placed the same plant in direct sunlight, it produced a gas that turned a glowing ember into a burning inferno. The plant again produced oxygen.

Ingenhousz showed that this gas production depended on sunlight. He continued his experiments and showed that plants did not produce new mass (leaf, stem, or twig) by absorbing matter from the ground (as others believed). The ground did not lose mass as a plant grew. Ingenhousz showed that new plant growth must come from sunlight. Plants captured carbon from carbon dioxide in the air and converted it into new plant matter in the presence of sunlight.

Ingenhousz had discovered the process of photosynthesis. He proved that plants created new mass “from the air” by fixing carbon with sunlight. In 1779 he published his results in Experiments Upon Vegetables. The name photosynthesis was created some years later and comes from the Greek words meaning “to be put together by light.”

Fun Facts: Some species of bamboo have been found to grow at up to 91 cm (3 ft.) per day. You can almost watch them grow!

Oceans control Global Weather

By pumping massive amounts of heat through the oceans, vast ocean currents control weather and climate on land.

  • Who Discovered it: Benjamin Franklin.
  • Year of Discovery: 1770


How was it Discovered?

The Atlantic Ocean’s Gulf Stream is the most important of our world’s ocean currents. It is a major heat engine, carrying massive amounts of warm water north to warm Europe. It has directed the patterns of ocean exploration and commerce and may be a major determinant of the onset of ice ages. Finally, it is the key to understanding global circulation patterns and the inter-connectedness of the world’s oceans, weather, and climates.

American statesman, inventor, and scientist Benjamin Franklin conducted the first scientific investigation of the Gulf Stream and discovered its importance to Earth’s weather and climate. His work launched a scientific study of ocean currents, ocean temperature, the interaction of ocean current with winds, and the effect of ocean currents on climate. Franklin’s discoveries mark the beginnings of modern oceanographic science.

Benjamin Franklin set out to map the Gulf Stream in order to speed transatlantic shipping. He wound up discovering that ocean currents are a major controlling factor of global climate and weather.

Ocean surface currents were noted by early Norse sailors as soon as they sailed the open Atlantic. Columbus and Ponce de Leon described the Gulf Stream current along the coast of Florida and in the strait between Florida and Cuba. Others noted North Atlantic currents over the next hundred years. However, no one charted these currents, recorded them on maps, or connected the individual sightings into a grand, ocean-wide system of massive currents.

In 1769 British officials in Boston wrote to London complaining that the British packets (small navy ships that brought passengers and mail to the colonies) took two weeks longer in their trans-Atlantic crossing than did American merchant ships. Benjamin Franklin, an American representative in London at the time, heard this report and refused to believe it. Packet ships rode higher in the water, were faster ships, and were better crewed than heavy Rhode Island merchant ships.

Franklin mentioned the report to a Rhode Island merchant captain off-loading cargo in London. This captain said it was absolutely true and happened because Rhode Island whalers had taught American merchant captains about the Gulf Stream, a 3 mph current that spread eastward from New York and New England toward England. American captains knew to curve either north or south on westward trips to avoid fighting this powerful current.

When Franklin checked, the Gulf Stream didn’t appear on any maps, nor did it appear in any of the British Navy shipping manuals. Franklin began interviewing merchant and whaling captains, recording on maps and charts their experience with the Gulf Stream current. Whalers, especially, knew the current well because whales tended to congregate along its edges.

By 1770 Franklin had prepared detailed maps and descriptions of this current. British Navy and merchant captains, however, didn’t believe him and refused to review his information. By 1773 rising tensions between England and the colonies made Franklin withhold his new findings from the British.

Franklin began taking regular water temperature readings on every Atlantic Ocean crossing. By 1783 he had made eight crossings, carefully plotting the exact course his ship took each time and marking his temperature readings on the ship’s map.

On his last voyage from France to America, Franklin talked the ship’s captain into tracking the edge of the Gulf Stream current. This slowed the voyage as the ship zigzagged back and forth using the warm water temperature inside the Gulf Stream and the colder water temperature outside it to trace the current’s boundary.

The captain also allowed Franklin to take both surface and subsurface (20 and 40 fathoms) temperature readings. Franklin was the first to consider the depth (and thus the volume) of an ocean current.

Franklin discovered that the Gulf Stream poured masses of warm water (heat) from the tropical Caribbean toward northern Europe to warm its climate. He began to study the interaction between wind and current and between ocean currents and weather. Through the brief papers he wrote describing the Gulf Stream data he had collected, Franklin brought science’s attention and interest to ocean currents and their effect on global climate.

Franklin’s description of the Gulf Stream was the most detailed available until German scientist Alexander von Humbolt published his 1814 book about the Gulf Stream based on his measurements from more than 20 crossings. These two sets of studies represent the beginnings of modern oceanographic study.

Fun Fact: The Gulf Stream is bigger than the combined flow of the Mississippi, the Nile, the Congo, the Amazon, the Volga, the Yangtze, and virtually every other major river in the world.

Distance to the Sun

“The first accurate calculation of the distance from the earth to the sun, of the size of the solar system, and even of the size of the universe.”

  • Who Discovered it: Giovanni Cassini
  • Year of Discovery: 1672

How was it Discovered?


Our understanding of the universe depends on two foundations—our ability to measure the distances to faraway stars, and our ability to measure the chemical composition of stars. The discovery that allowed scientists to determine the composition of stars is described in the 1859 entry on spectrographs. The distance to the sun has always been regarded as the most important and fundamental of all galactic measurements. Cassini’s 1672 measurement, however, was the first to accurately estimate that distance.

Cassini’s discovery also provided the first shocking hint of the truly immense size of the universe and of how small and insignificant Earth is. Before Cassini, most scientists believed that stars were only a few million miles away. After Cassini, scientists realized that even the closest stars were billions (if not trillions) of miles away!
Born in 1625, Giovanni Cassini was raised and educated in Italy. As a young man, he was fascinated by astrology, not astronomy, and gained widespread fame for his astrological knowledge. Hundreds sought his astrological advice even though he wrote papers in which he proved that there was no truth to astrological predictions.
In 1668, after conducting a series of astronomical studies in Italy that were widely praised, Cassini was offered a position as the director of the Paris Observatory. He soon decided to become a French citizen and changed his name to Jean Dominique Cassini.
With an improved, high-powered telescope that he carefully shipped from Italy, Cassini continued a string of astronomical discoveries that made him one of the world’s most famous scientists. These discoveries included the rotational periods of Mars and Saturn, and the major gaps in the rings of Saturn—still called the Cassini gaps.
Cassini was also the first to suspect that light travelled at a finite speed. Cassini refused to publish his evidence, and later even spent many years trying to disprove his own theory. He was a deeply religious man and believed that light was of God. Light, therefore, had to be perfect and infinite, and not limited by a finite speed of travel. Still, all of his astronomical work supported his discovery that light travelled at a fixed and finite speed.
Because of his deep faith in the Catholic Church, Cassini also believed in an Earth-centered universe. By 1672, however, he had become at least partially convinced by the early writing of Kepler and by Copernicus’s careful arguments to consider the possibility that the sun lay at the centre.
This notion made Cassini decide to try to calculate the distance from the earth to the sun. However, it was difficult and dangerous to make direct measurements of the sun (one could go blind). Luckily, Kepler’s equations allowed Cassini to calculate the distance from the earth to the sun if he could measure the distance from the earth to any planet.
Mars was close to Earth and well-known to Cassini. So he decided to use his improved telescopes to measure the distance to Mars. Of course, he couldn’t actually measure that distance. But if he measured the angle to a spot on Mars at the same time from two different points on Earth, then he could use these angles and the geometry of triangles to calculate the distance to Mars.
To make the calculation work, he would need to make that baseline distance between his two points on Earth both large and precisely known. He sent French astronomer Jean Richer to Cayenne in French Guiana off the north coast of South America. Cassini stayed in Paris.
On the same August night in 1672, at exactly the same moment, both men measured the angle to Mars and placed it exactly against the background of distant stars. When Richer returned to Paris with his readings, Cassini was able to calculate the distance to Mars. He then used Kepler’s equations to discover that the distance to the sun had to be 87 million miles (149.6 million km). Modern science has found that Cassini’s calculation was only 7 percent of the true distance (just over 93 million miles).

Cassini went on to calculate the distances to other planets and found that Saturn lay a staggering 1,600,000,000 (1.6 billion) miles away! Cassini’s discoveries of distance meant that the universe was millions of times bigger than anyone had dreamed.


Fun Facts: The sun’s diameter is 1.4 million km (875,000 miles). It is approximately 109 times wider than the earth.

Erosion of Earth

The earth’s surface is shaped by giant forces that steadily, slowly act to build it up and wear it down.

  • Who Discovered it: James Hutton
  • Year of Discovery: 1792

How was it discovered?

In the eighteenth century, scientists still believed that Earth’s surface had remained unchanged until cataclysmic James Huttonevents (the great flood of Noah’s ark fame was the most often cited example) radically and suddenly changed the face of our planet.

They tried to understand the planet’s surface structures by searching for those few explosive events. Attempts to study the earth, its history, its land-forms, and its age based on this belief led to wildly inaccurate guesses and misinformation.

James Hutton discovered that the earth’s surface continually and slowly changes, evolves. He discovered the processes that gradually built up and wore down the earth’s surface. This discovery provided the key to understanding our planet’s history and launched the modern study of earth sciences.

In the 1780s, 57-year-old, more-or-less retired physician and farmer (and amateur geologist) James Hutton decided to try to improve on the wild guesses about the age of the earth that had been put forth by other scientists. Hutton decided to study the rocks of his native Scotland and see if he could glean a better sense of Earth’s age by studying the earth’s rocks.

Lanky Hutton walked with long pendulum-like strides across steep, rolling green hills. Soon he realized that the existing geological theory—called catastrophism—couldn’t possibly be right. Catastrophism claimed that all of the changes in the earth’s surface were the result of sudden, violent (catastrophic) changes. (Great floods carved out valleys in hours. Great wrenchings shoved up mountains overnight.) Hutton realized that no catastrophic event could explain the rolling hills and meandering river valleys he hiked across and studied.

It was one thing to say that an existing popular theory was wrong. But it was quite another to prove that it was wrong or to suggest a replacement theory that better explained Earth’s actual surface. Hutton’s search broadened as he struggled to discover what forces actually formed the hills, mountains, valleys, and plains of Earth.

Late that summer Hutton stopped at a small stream tumbling out of a steep canyon.
Without thinking, he bent down and picked up a handful of tiny pebbles and sand from the stream bed. As he sifted these tiny rocks between his fingers, he realized that these pebbles had drifted down this small stream, crashing and breaking into smaller pieces as they went.

They used to sit somewhere up higher on the long ridge before him. This stream was carrying dirt and rock from hilltop to valley floor. This stream was reshaping the entire hillside—slowly, grain by grain, day by day. Not catastrophically as geologists claimed.

The earth, Hutton realized, was shaped slowly, not overnight. Rain pounding down on hills pulled particles of dirt and rock down into streams and then down to the plains. Streams gouged out channels, gullies, and valleys bit by bit, year by year.

The wind tore at hills in the same way. The forces of nature were everywhere tearing down the earth, levelling it out. Nature did this not in a day, but over countless centuries of relentless, steady work by wind and water. Then he stopped. If that were true, why hadn’t nature already levelled out the earth? Why weren’t the hills and mountains worn down? There must be a second force that builds up the land, just as the forces of nature tear it down.

For days James Hutton hiked and pondered. What built up the earth? It finally hit him: the heat of Earth’s core built up hills and mountains by pushing outward. Mountain ranges were forced up by the heat of the earth. Wind and rain slowly wore them back down. With no real beginning and no end, these two great forces struggled in dynamic balance over aeons, the real-time scale for geologic study.

With that great discovery, James Hutton forever changed the way geologists would look at the earth and its processes, and he completely changed human kind’s sense of the scale of time required to bring about these changes.