Now that the weather has turned cold in the northern part of the Northern Hemisphere, our thoughts are turning to snow and ice. Many of us take advantage of the winter weather by ice skating, skiing, or snowboarding. But what if we had more snow or ice - let's say about 5,000 feet of snow and ice - rising above where your house stands today?
Does that sound crazy? It sure sounded crazy to people in the early 1800s, when the Ice Age theory was first proposed. But like many radical theories about Earth's past, it was later proved to be true.
Let's take a look at three "crackpot" theories that have changed the way we look at Earth's past:
Many years ago - 167 years ago, to be exact - a Swiss naturalist named Louis Agassiz (AG-uhs-see) proposed the theory of the Great Ice Age. Agassiz grew up in the Swiss Alps and was very familiar with alpine (mountain) glaciers and their effects on the landscape. One day two of his friends took him to see an alpine glacier and pointed out big boulders (called erratics) strewn across a valley well below the glacier. Agassiz and his friends recognized that these huge boulders must have been carried into the valley by a strong force - a glacier. But how could that be? The glacier was way up the mountainside.
Then Agassiz's friends pointed to ridges of gravel, sand, and boulders that marked the front edge of where a glacier had once stood. At that time, naturalists who studied glaciers knew that these very slow moving "ice rivers" scoured the land beneath them. They also picked up and carried everything in their path. And because of the way the ice in a glacier moves, any debris that a glacier has picked up will be deposited at the front edge of a glacier. That's what creates these ridges of material, called moraines.
This was a "Eureka!" moment for Agassiz. Suddenly, everywhere he looked he saw evidence that glaciers had been there. He saw erratics where they shouldn't be, far from the bedrock from which they had broken off. He saw glacial moraines where others just saw gravel banks. In places like Scotland, which is thousands of miles from the nearest glacier, Agassiz saw rocks with long striations - scratches or gouges - on them. The striations indicated the presence of a once flowing glacier.
Agassiz collected his thoughts and presented them in a lecture in 1837. Three years later, his book "Studies on Glaciers" was published. In it, he proposed that "a huge ice sheet ... extended beyond the shorelines of the Mediterranean and of the Atlantic Ocean, and even completely covered North America and Asiatic Russia."
Scientists hotly debated the idea of glaciers the size of continents for decades. Eventually, though, they came to accept Agassiz's theory. Not only that, but other scientists concluded that there had been not just one, but many Ice Ages in our past.
Alfred Wegener was an early 20th-century German meteorologist. He had a PhD in astronomy, but dropped it to study meteorology, the new science of weather. During the school year he was a popular lecturer on meteorology at the University of Marburg in Germany. For several summers he joined or led expeditions to Greenland. (Exploring Greenland was his lifelong passion.)
In 1910, Wegener happened to notice on a map that the coastlines of South America and Africa looked as though they had once fitted together, like pieces of a jigsaw puzzle. He was not the first to notice this; it was first noted by a 16th-century mapmaker. Perhaps you've noticed it, too. But Wegener became obsessed with the idea of explaining how this could be. He gave his first lecture on the topic in January 1912. That's where he put forth the idea of "continental displacement" or what later was called "continental drift." (That same year, incidentally, he returned to Greenland and set a record for the longest crossing of the ice cap on foot.)
Wegener published his ideas on continental drift in 1915. His theory: Long ago, all the land on Earth was joined together like a gigantic jigsaw puzzle. He called this supercontinent Pangea. Pangea began to break apart 200 million years ago, and the continents "drifted" to their present positions.
Wegener was dismissed by most of the scientific community. In turn, he called his colleagues "narrow-minded." The problem with his theory of continental drift was explaining how the continents moved. What was the mechanism? Geologic evidence supported Wegener: Similar fossils of the same age were found on both sides of the Atlantic. In some places one could see how geologic strata (layers of rock) lined up across the ocean. But how had the continents moved apart?
In 1930, Wegener sailed from Denmark as the leader of a major expedition to Greenland. Sadly, he did not return, but died during the expedition. He had never explained how the continents moved.
Thirty-two years later, in 1962, Harry Hess completed Wegener's theory. Hess proposed sea-floor spreading.
Princeton geologist Hess noticed that the newest continental crust is along the Mid-Atlantic Ridge, deep under the Atlantic Ocean. There, the sea floor is "spreading," or growing, by up to 5 centimeters per year. Hess theorized that the surface of the earth is made up of enormous plates. Where two or more plates meet, earthquakes and volcanoes occur - evidence that the plates move. Today, the theory of continental drift and plate tectonics (from a Greek word meaning "to build") is well-established.
Pictures of dinosaurs, dinosaur toys, even dinosaur movies are so common today that it's hard to believe that the word "dinosaur" is only 160 years old. That's when Richard Owen, an English doctor, first coined the term for the "fossil reptiles." It's a combination of two Greek words: deinos ("fearfully great") and sauros ("lizard"). Since the first fossils were discovered, dinosaurs have captured our imagination. They're particularly intriguing because they seem to have simply disappeared off the face of the earth.
Did you ever see the movie "Fantasia"? Do you remember the dinosaur sequence? It showed dinosaurs trudging through a barren, desertlike landscape. Scientists have believed for a long time that some sort of massive climate change had wiped out the dinosaurs (and 50 percent of all animal species on earth) 65 million years ago.
In 1980, four people - including physicist Luis Alvarez and his geologist son Walter - published a paper proposing their theory that dinosaurs became extinct when an asteroid or comet hit the earth.
This theory was - and still is - big news in the geology world. The scientists based their theory on something they had found by looking closely at the geologic record. Between the Cretaceous and the Tertiary period ("the K-T boundary," researchers call it), they found high levels of iridium and "shocked" quartz. Iridium is an element found mostly in objects from outer space. "Shocked" quartz indicates some kind of enormous impact. They theorized that a giant meteorite, 10 kilometers (6 miles) in diameter, had crashed into the earth while going thousands of miles an hour. The impact would have raised an immense dust cloud that would have blocked or dimmed the sun for many years, creating a dramatic change in the world's climate.
In 1990, the Chicxulub crater in the Yucatan peninsula in Mexico was discovered. This impact crater - about 200 km (120 miles) in diameter - dates to about 65 million years ago. That makes it a prime candidate for being the crater of the asteroid linked to the dinosaurs' extinction.
Recently, a 2.5 mm meteorite (1/10th of an inch) was found in the North Pacific. The meteorite is thought to be 65 million years old and may have come from the large meteor that crashed into the Yucatan - breaking off as the meteor entered Earth's atmosphere.
There's still controversy over this theory. Some say that massive volcanic activity led to climate change 65 million years ago. This last theory is still an unfolding story ... so stay tuned.