Ice Age - Definition and Timeline

Ice Age - Definition and Timeline

An ice age is a period of colder global temperatures and recurring glacial expansion capable of lasting hundreds of millions of years. Thanks to the efforts of geologist Louis Agassiz and mathematician Milutin Milankovitch, scientists have determined that variations in the Earth’s orbit and shifting plate tectonics spur the waxing and waning of these periods. There have been at least five significant ice ages in Earth’s history, with approximately a dozen epochs of glacial expansion occurring in the past 1 million years. Humans developed significantly during the most recent glaciation period, emerging as the dominant land animal afterward as megafauna such as the wooly mammoth went extinct.

An ice age is a period of colder global temperatures that features recurring glacial expansion across the Earth’s surface. Capable of lasting hundreds of millions of years, these periods are interspersed with regular warmer interglacial intervals in which at least one major ice sheet is present. Earth is currently in the midst of an ice age, as the Antarctic and Greenland ice sheets remain intact despite moderate temperatures.

These global cooling periods begin when a drop in temperature prevents snow from fully melting in some areas. The bottom layer turns to ice, which becomes a glacier as the weight of accumulated snow causes it to slowly move forward. A cyclical pattern emerges in which the snow and ice traps the Earth’s moisture, fueling the growth of these ice sheets as the sea levels simultaneously drop.

An ice age causes enormous changes to the Earth’s surface. Glaciers reshape the landscape by picking up rocks and soil and eroding hills during their unstoppable push, their sheer weight depressing the Earth’s crust. As temperatures drop in areas adjacent to these ice cliffs, cold-weather plant life is driven to southern latitudes. Meanwhile, the dramatic drop in sea levels enables rivers to carve out deeper valleys and produce enormous inland lakes, with previously submerged land bridges appearing between continents. Upon retreating during warmer periods, the glaciers leave behind scattered ridges of sediment and fill basins with melted water to create new lakes.

Scientists have recorded five significant ice ages throughout the Earth’s history: the Huronian (2.4-2.1 billion years ago), Cryogenian (850-635 million years ago), Andean-Saharan (460-430 mya), Karoo (360-260 mya) and Quaternary (2.6 mya-present). Approximately a dozen major glaciations have occurred over the past 1 million years, the largest of which peaked 650,000 years ago and lasted for 50,000 years. The most recent glaciation period, often known simply as the “Ice Age,” reached peak conditions some 18,000 years ago before giving way to the interglacial Holocene epoch 11,700 years ago.

At the height of the recent glaciation, the ice grew to more than 12,000 feet thick as sheets spread across Canada, Scandinavia, Russia and South America. Corresponding sea levels plunged more than 400 feet, while global temperatures dipped around 10 degrees Fahrenheit on average and up to 40 degrees in some areas. In North America, the region of the Gulf Coast states was dotted with the pine forests and prairie grasses that are today associated with the northern states and Canada.

The origins of ice age theory began hundreds of years ago, when Europeans noted that glaciers in the Alps had shrunk, but its popularization is credited to 19th century Swiss geologist Louis Agassiz. Contradicting the belief that a wide-ranging flood killed off such megafauna as the wooly mammoth, Agassiz pointed to rock striations and sediment piles as evidence of glacier activity from a destructive global winter. Geologists soon found evidence of plant life between glacial sediment, and by the close of the century the theory of multiple global winters had been established.

A second important figure in the development of these studies was Serbian mathematician Milutin Milankovitch. Seeking to chart the Earth’s temperature from the past 600,000 years, Milankovitch carefully calculated how orbital variations such as eccentricity, precession and axial tilt affected solar radiation levels, publishing his work in the 1941 book Canon of Insolation and the Ice Age Problem. Milankovitch’s findings were corroborated when technological improvements in the 1960s allowed for the analyzation of deep sea ice cores and plankton shells, which helped pinpoint periods of glaciation.

Along with solar radiation levels, it is believed that global warming and cooling is connected to plate tectonic activity. The shifting of the Earth’s plates creates large-scale changes to continental masses, which impacts ocean and atmospheric currents, and triggers volcanic activity that releases carbon dioxide into the air.

One significant outcome of the recent ice age was the development of Homo sapiens. Humans adapted to the harsh climate by developing such tools as the bone needle to sew warm clothing, and used the land bridges to spread to new regions. By the start of the warmer Holocene epoch, humans were in position to take advantage of the favorable conditions by developing agricultural and domestication techniques. Meanwhile, the mastodons, saber-toothed cats, giant ground sloths and other megafauna that reigned during the glacial period went extinct by its end.

The reasons for the disappearance of these giants, from human hunting to disease, are among the ice age mysteries that have yet to be fully explained. Scientists continue to study the evidence of these important periods, both to gain more insight into the Earth’s history and to help determine future climatic events.

What Was the Little Ice Age?

When most people think of ice ages, or “glacial ages,” they often envision cavemen, woolly mammoths, and vast plains of ice—such as those that occurred during the Pleistocene (about 2.6 million to 11,700 years ago) or the late Carboniferous and early Permian periods (about 300 million years ago). During these parts of Earth’s past, mile-high ice sheets covered large parts of continents, and their presence affected the weather and climate throughout the world. In fact, during one prehistoric period, the Cryogenian (which spanned roughly 720 million to 635 million years ago), there is evidence to support the notion that the whole planet was either locked in ice or possibly covered in ice with only a thin film of slush near the Equator. Think present-day Europa or Enceladus. What about the relatively recent “Little Ice Age”? Was it a true glacial age? Yes and no.

Of course, the severity of the Little Ice Age, which lasted from the early 14th century through the mid-19th century, was not a deep freeze like the long ice ages of the ancient past. After all, human civilization thrived and expanded during the Little Ice Age, as several civilizations sent ships to explore, colonize, and exploit new lands.

Nevertheless, images depicted in paintings, data from ships’ logs and scientific reports of the time, and other historical writings have shown that many parts of Europe experienced cooler than normal conditions during this time. Since the people of the time did not keep accurate weather records (to the extent that we do now), present-day scientists looking to understand the climate of the Little Ice Age have relied on proxy records—that is, indirect sources of climatic information (such as coral growth, cores of lake sediments, ice cores, and annual rings in trees)—to better understand the regional and global climates of the time. Proxy records showed that mountain glaciers grew during the Little Ice Age at several locations—including the European Alps, New Zealand, Alaska, and the southern Andes—and mean annual temperatures across the Northern Hemisphere fell by 0.6 °C (1.1 °F) relative to the average temperature between 1000 and 2000 CE. Proxy records collected from western Greenland, Scandinavia, the British Isles, and western North America point to several cool episodes, lasting several decades each, when temperatures dropped 1 to 2 °C (1.8 to 3.6 °F) below the thousand-year averages for those areas. These regional temperature declines, however, rarely occurred at the same time. In addition, temperatures of other regions (such as in eastern China and in the Andes Mountains of South America) were fairly stable, while still other regions (such as southern Europe, North America’s Mississippi Valley, and parts of Africa and Asia) became drier, with droughts lasting several years at a time.

So what caused the Little Ice Age? It was likely a combination of factors that included long periods of low sunspot activity (which reduced the amount of solar energy that reached Earth), the effects of explosive volcanic eruptions, and drastic changes in the North Atlantic Oscillation (the irregular fluctuation of atmospheric pressure over the North Atlantic Ocean).

Although the Little Ice Age was not a formal ice age, one could certainly argue that it was a significant phenomenon associated with a variety of climatic changes affecting many disparate parts of the world. Earth’s climate changes often through time, so this cool 450-year slice of Earth’s history was not the only one of its kind. There have been warm intervals too. One example is the recent warming (caused by a mix of natural factors and human activities) that began after the Little Ice Age ended and continues to this day. Another example is the highly controversial medieval warm period—another time of relative warmth—which, according to some scientists, lasted from 900 to 1300 CE. Unlike the Little Ice Age and the recent period of warming, however, there is a great deal of disagreement with respect to the reach of the medieval warm period or whether it even happened at all.

Why do glacial periods end abruptly?

Notice the asymmetric shape of the Antarctic temperature record (black line), with abrupt warmings shown in yellow preceding more gradual coolings (Kawamura et al. 2007 Jouzel et al. 2007). Warming at the end of glacial periods tends to happen more abruptly than the increase in solar insolation. Several positive feedbacks are responsible for this. One is the ice-albedo feedback. A second feedback involves atmospheric CO2. Direct measurement of past CO2 trapped in ice core bubbles shows that the amount of atmospheric CO2 decreased during glacial periods (Kawamura et al. 2007 Siegenthaler et al. 2005 Bereiter et al. 2015), in part because the deep ocean stored more CO2 due to changes in either ocean mixing or biological activity. Lower CO2 levels weakened the atmosphere's greenhouse effect and helped to maintain lower temperatures. Warming at the end of the glacial periods liberated CO2 from the ocean, which strengthened the atmosphere's greenhouse effect and contributed to further warming.

The Institute for Creation Research

Many Christians are convinced that scientific data demand millions of years for Earth&rsquos history and are therefore dissuaded from believing the Bible&rsquos doctrine of a recent creation. Yet a belief in millions of years actually prevents secular scientists from finding solutions for many mysteries of Earth history&mdashsolutions that can be found in the pages of God&rsquos Word. For instance, the Bible, with its short 6,000-year timescale and account of a global flood, is the key to explaining the Ice Age. 1

Secular Ice Age Theories Are Inadequate

Secular scientists do not have a good explanation for what causes an ice age. In 1997, U.S. News & World Report described this as one of the &ldquogreat mysteries of science,&rdquo stating:

Yet despite the efforts of marine geologists, atmospheric chemists, oceanographers, and more, no one knows what caused the ice ages. &ldquoWe&rsquove been chewing on this problem for 30 or 40 years,&rdquo says Alan Mix, an oceanographer at Oregon State University. &ldquoIt&rsquos a killer.&rdquo Adds Ralph Cicerone, dean of physical sciences at the University of California&ndashIrvine, &ldquoIt&rsquos embarrassing.&rdquo 2

Not much has changed since then. The precise causes of ice ages &ldquoremain controversial&rdquo 3 and are &ldquonot completely understood.&rdquo 4 Secular scientists continue to propose new explanations, 5 which is an indication that none of the current ones are very convincing.

Of these explanations, the astronomical (or Milankovitch) ice age theory is the most popular. It holds that slow changes in Earth&rsquos orbital and rotational motions cause differences in the way sunlight falls on the earth&rsquos surface. Supposedly these differences control the timing of ice ages.

However, the changes in sunlight are so small that it&rsquos difficult to see how they alone could cause an ice age. Famed evolutionary astronomer Fred Hoyle once ridiculed the astronomical theory:

If I were to assert that a glacial condition could be induced in a room liberally supplied during winter with charged night-storage heaters simply by taking an ice cube into the room, the proposition would be no more unlikely than the Milankovitch theory. 6

The Milankovitch theory became widely accepted because of a 1976 paper titled &ldquoPacemaker of the Ice Ages.&rdquo 7 This paper used uniformitarian assumptions to claim that data within two deep-sea sediment cores told a story of climate change that agreed with the theory&rsquos expectations. However, this &ldquoconfirmation&rdquo of the astronomical theory depended upon an age assignment that secular scientists themselves no longer believe to be valid. 8 The argument is dramatically weakened when this age revision and other changes to the data are taken into account. 9

The Biblical Model

Creation scientist and meteorologist Michael Oard has presented strong arguments that the Genesis Flood caused the Ice Age. 10,11 Most creationists think that during the Flood the original ocean floor was rapidly subducted into the earth&rsquos mantle and was replaced by new seafloor that formed at the mid-ocean ridges. The heat from the newly formed seafloor significantly warmed the world&rsquos oceans, resulting in greatly increased evaporation from the sea&rsquos surface. 12 This dramatically increased the moisture in the atmosphere and led to greater precipitation, including more snowfall at high latitudes and on mountaintops.

Subduction zone volcanoes continued to erupt for centuries after the Flood, gradually decreasing in number and intensity. They ejected aerosols (tiny particles and droplets) into the atmosphere that reflected significant amounts of sunlight, resulting in cooler summers that prevented winter snow and ice from melting. As the snow and ice accumulated year after year, thick ice sheets formed (Figure 1).

The model developed by Oard makes good meteorological sense. Furthermore, creation researcher and atmospheric scientist Dr. Larry Vardiman used standard meteorological computer models to simulate the effect of warm oceans on precipitation rates. His results demonstrated that very warm waters would dramatically increase snowfall in Yellowstone and Yosemite National Parks, which are known to have been covered by thick ice sheets during the Ice Age. 13,14

Likewise, recent volcanic eruptions have demonstrated that large, explosive, sulfur-rich eruptions can cause noticeable global cooling, particularly during the summer and autumn months. 15 Both creation and secular scientists agree that past volcanic activity dwarfed anything we see happening today, so these past eruptions definitely had the potential for dramatic summer cooling.

&ldquoMillions of Years&rdquo Are the Problem

If this scenario makes sense, why can&rsquot secular scientists use warm oceans and volcanic cooling to explain the Ice Age? First, it would take an enormous amount of energy to significantly warm the world&rsquos oceans. This would require cataclysmic conditions that violate their uniformitarian assumption that &ldquothe present is the key to the past.&rdquo But the Genesis Flood, which they deny, is an ideal candidate for such ocean warming.

Likewise, secular scientists cannot invoke volcanic cooling because of their belief in millions of years of Earth history. They insist that large eruptions&mdashwhich are known to have occurred&mdashwere separated from one another by vast ages. Hence, any cooling they might have provided would be greatly diluted by the assumed long ages between eruptions. This is a clear example of how a belief in millions of years hinders scientific research.

Many Ice Ages or Just One?

Although secular scientists insist that about 50 Pleistocene ice ages have occurred within the last 2.6 million years, there is strong geological evidence for just the most recent one, which creation scientists argue was the only Ice Age. Even secular scientists have acknowledged that a single ice age could explain the geological evidence found in western Canada. 16

The main argument for 50 Pleistocene ice ages is, believe it or not, a Milankovitch interpretation of chemical measurements obtained from deep-sea sediment cores. Secular scientists used 57 deep-sea cores to construct a composite &ldquostack&rdquo of chemical data called oxygen isotope, or &delta 18 O, values that supposedly covers the last 5.3 million years of prehistory. 17 These scientists think each oxygen isotope &ldquowiggle&rdquo cycle represents a cold/warm ice age-interglacial cycle. They simply counted the number of cycles dated as younger than 2.6 million years. Since they counted around 50 wiggles (Figure 2), voilà!&mdashthere were 50 supposed Pleistocene ice ages! But as noted earlier, evidence for the Milankovitch theory is weak at best.

Secular scientists also claim that other major ice ages occurred hundreds of millions of years ago. Some even say the entire earth froze in an event called Snowball Earth. However, the evidence for this claim is also weak. Because rocks embedded in moving glaciers scratch the underlying bedrock, geologists sometimes interpret such scratches as evidence for past glaciers. They have found scratches in locations thought to be near the equator in the very distant past, which they interpret to mean that at one point glaciers grew so large they extended all the way to the equator, covering the entire earth. But debris flows can also cause such scratches, and creation scientists have made strong arguments that the scratches were actually caused by giant underwater landslides during the Genesis Flood. 18,19

Wooly Mammoths in Siberia

Michael Oard&rsquos biblical model also solves another major mystery of Earth history: How did millions of wooly mammoths (Figure 3) thrive in Siberia during the Ice Age? There is strong evidence that large numbers of these animals lived there during this time. Today winters in Siberia are bitterly cold. Lows of -40°F are typical, and temperatures colder than the surface of Mars have been recorded. 20 How could even the wooly mammoths have endured such temperatures?

Moreover, secular scientists think that Earth is currently in a warm interglacial period, so Siberian Ice Age temperatures would presumably have been even colder. Even if mammoths could somehow tolerate those temperatures, how could these huge creatures find sufficient food and water in such a harsh climate? And a number of factors, such as long gestation times, would have made it difficult, if not impossible, for mammoths to migrate to warmer areas during the Siberian winters.

The only logical explanation is that, for some reason, the Siberian climate was more temperate during the Ice Age than it is today. Oard&rsquos model provides a simple, straightforward explanation for this surprising result. Oceans would have remained warm for hundreds of years after the Flood. In fact, there would have been no Arctic sea ice during the Ice Age. Warm, moist ocean air helped to moderate the Siberian climate in much the same way that warm, moist air from the Pacific Ocean helps to moderate the climate of Seattle, Washington, today. Although Siberian winters were still cold during the Ice Age, they would have been tolerable for the wooly mammoths. 1 This also explains why the coastal lowlands of Siberia were never covered by ice, even though secular ice age models predict that they would have been. 10

Secular scientists can&rsquot use this simple explanation because according to their evolutionary story, Arctic sea ice has been present for at least the last 100,000 years, 21 long before the time they think the mammoths went extinct about 10,000 years ago. This means that according to the secular model, Arctic sea ice was present while the mammoths lived in Siberia. With sea ice present and warm oceans absent, Siberia would have been as cold as it is today, if not more so. So again, secular scientists&rsquo belief in millions of years prevents them from seeing a straightforward explanation for this well-known mystery.

Oard&rsquos model also explains why the mammoths went extinct. As the Ice Age ended, tremendous volumes of fresh meltwater flowed to the Arctic Ocean. Being less dense than salt water, this fresh water remained on top of the sea&rsquos surface and froze, forming a layer of sea ice. With the climate-moderating influence gone, temperatures quickly dropped, and the mammoths succumbed to the colder temperatures. 22 Using basic meteorological reasoning, Oard shows that these colder high-latitude temperatures, combined with a dryer climate at the end of the Ice Age, would have resulted in enormous dust storms, which overtook and buried some of the mammoths. After burial, the dust froze around their remains. This is why many Siberian mammoth carcasses are found in frozen hills of wind-blown silt called loess. 1

The Bible&rsquos History Is the Solution

Christians don&rsquot need to accept the millions of years projected by secular scientists. Time after time, the scientists&rsquo deep-time theories fail to provide adequate explanations. The biblical timeline, however, is a different story. It is not a problem or an embarrassment for which Christians need to apologize. Rather, it&rsquos the key to making sense of Earth&rsquos history!

Transcript [ edit ]

Note there are several spelling errors in the comic, so please do only correct spelling errors that are not part of the comic! See more in the trivia section.

[A large heading, followed by a sub-caption. Below that two lines with a statement in between:] A timeline of Earth’s average temperature since the last ice age glaciation When people say “The climate has changed before,” these are the kinds of changes they’re talking about. [A very long chart below the headings above is headed with a label for the scale of the X-axis above the chart. Below that a sub-caption. To the left an arrow down to the top of the chart pointing to the dotted curves starting point (at -4.3°C below the 1961-1990 average) with a label above the arrow. And arrow pointing left to the left of the center and another pointing right to the right of the center has labels. Below these is the temperature scale of the X-axis, with 9 ticks between the borders each with a label ranging from -4 to +4°C compared to the 1961-1990 average, but with another step in each direction not labeled towards to axis so the chart covers -5 to +5°C compared to the 1961-1990 average.] Temperature Compared to the 1961-1990 average Start Colder Warmer -4°C -3°C -2°C -1°C 0°C +1°C +2°C +3°C +4°C [To the right of the chart is a gray text standing on the side down along the outer boarder of the chart with the sources for the chart:] Source: Shakun et. al. (2012) , Marcott et. al. (2013), Annan and Hargreaves (2013) , HadCRUT4, IPCC [The chart is split in 10 columns by the temperature scale and the borders. The two central columns are white, and then from there to the left the background becomes a faded color that changes from light blue to blue at the edge in four steps. Similarly to the right the color changes from light red to red. To the left there is a time scale taking 500 years leaps from 20,000 BCE all the way to year 1, where there are two years, one for BBC and one for CE. The 500 year leaps continue until 1500 CE and from there the steps are down to 100 years until 2100 with also present day 2016 labeled. After 1500 the CE is omitted. The labels stop there, but there is space below covering down to 2200 CE. There is clearly visible division line across the chart on the level of each of the 500 step, and fainter lines for each of the 100 steps all the way even though only the last 5 of these 100 steps are labeled. There is a similar clear line at 2016. Below each step on the Y-axis is noted, and then any text starting before the next step is noted below indented. If there are extra image belonging to text this is indented once more. The graph that the whole chart is about is a dotted line that begins at the “start” point mentioned above at -4.3°C and then begins to go straight down. It will change left and right all the way down. To being with all text and most drawings are to right of the dotted curve. Whenever something is to the left it will be noted. When it says to the left above something, and then nothing over the next, then the next will be to the right. Only at the very bottom are there more entries to the left than right. ] 20000 BCE [An arrow goes from the dotted line to the central line at 0°C. In the middle of the line there is a temperature label:] 4.3°C At the start of our timeline, 22,000 years ago, Earth is 4°C colder than during the late 20 th century. Boston is buried under almost a mile of ice, and the glaciers reach as far south as New York City. [The Statue of Liberty is shown in front of a glacier front. A very tiny Cueball is on top of the glacier. The drawing is labeled and so is also the glacier.] New York Ice [Cueball (wearing a knit cap with a pom-pom is seen walking in a snowy landscape leaving black footprints behind him. He walks through the white central part of the chart.] [The skyline of Boston is shown with two clear buildings among all the other. Above it is a line and in between this area has been filled with thin lines. The drawing is labeled and so is this area. Also the skyline has an arrow pointing at it with a label:] Boston Ice Modern skyline 19500 BCE But the world is about to warm up. By this time, humans have already spread across Africa, Eurasia, and Australia. They’ve created painting, pottery, rope, and bows and arrows, but haven’t developed writing or farming. 19000 BCE Changes in the Earth’s orbit mean that more sunlight reaches the polar ice… [A line chart with a labeled Y-axis with three labeled ticks. The curve starts up and then goes down five times and up four times ending down. There is one plateau towards the end compared to the rest of the curve where the ups and downs are quite alike.] Summer sun W/m 2 at 60°N 550 500 450 18500 BCE [A map of the world. At the top is a light gray area covering North America, Greenland and northern Europe and most of the northern part of Russia. A similar gray area covers Antarctica. There are two labels in the gray area above and one in the gray area below:] Ice Ice Ice 18000 BCE …And the ice sheets start to melt. 17500 BCE Temperatures have been creeping upward, but around this point, CO2 levels start to climb… 17000 BCE …And then the warming speeds up. 16500 BCE [Cueball is standing with a spear just the right of the graph talking to a rabbit.] Cueball: Still pretty cold. 16000 BCE [Megan points to the graph to the right of her and between her and Ponytail standing on the other side. Mean is the first drawing on the left side of the dotted curve, which has hardly moved since the beginning, only to just on the other side of 4°C.] [In the right part of the chart is an explanation of the data. Below the first two lines there are four drawings each showing possible temperature swings in reality compared to the smoothed data that represents the dotted curve of the entire chart. The dotted curve is shown in all four drawings and a thin line is shown running along it but with much more fluctuation left and right on the first two, a large spike right on the third and a large bump way right on the fourth. Above these there are two labels. The first labels is inside a bracket that covers the first three, and the last label is for the last drawing. Below is a list of sources.] Limits of this data: Short warming or cooling spikes might be “smoothed out” by these reconstructions but only if they’re small or brief enough. Possible Unlikely Reconstructions are from Shakun (2012) and Marcott (2013), scaled to Annan + Hargreaves (2013) estimate for the last glacial period. 15500 BCE In what is now France, humans paint murals on the walls of the Lascaux caves [Hairy paints three animals, two with horns, and two humans, Cueball holding hand with Hairy who has a spear. On the other side of the central line Megan writes three letters, the last of which is reversed.] NIИ 15000 BCE Ice sheets around Alaska shrink, exposing a land bridge between Asia and North America [From around the bottom if this section and down to 11500 BCE the dotted curve moved steadily to the right towards warmed temperature peaking close to -1.5°C. Before this the temperature had not moved much away from that at the start.] 14500 BCE [Cueball walks right looking back at the graph behind him. Megan walks in front of him pointing further right.] Cueball: Cool. Humans reach North America. 14000 BCE The edge of the ice withdraws from New York City and retreats North. [A large glacier front speaks in a speech bubble with an arrow pointing at it. Behind is there are four peaks in the horizon and in front of it three small melting pools and some rocks on the ground.] Glacier: That’s it! I’m moving to Canada! 13500 BCE Humans domesticate dogs (Date uncertain, may be much earlier) [Megan and Cueball is watching a wolf looking at them.] Megan: Okay, you can live in our homes and we’ll feed you, but we’ll still get mad f you poop on the floor. Wolf: Deal. Cueball: And we get to breed you to be tiny and dress you in little costumes. Wolf: …Wait. 13000 BCE [Randall did not use the normal spelling for Woolly Rhino, but this is an accepted alternative spelling:] Wooly Rhino goes extinct Oregon is scoured by huge floods as glacial dams burst and lakes of meltwater flow to the sea 12500 BCE Ice sheets withdraw from Chicago 12000 BCE Humans settle Abu Hureyra in Syria 11500 BCE [An arrow on the left side of the dotted curve is pointing down along the dotted curve and to the left indicate temperature is declining again, meaning the dotted curve now moves left to colder temperatures. This only continues until 10500 BCE. It is only the second time something is noted on the left side after Megan at 16000 BCE] Temperatures start to decline, mainly in the Northern hemisphere This may be caused by changes in ocean circulation due to the floods of cold fresh meltwater flowing into the Atlantic as the North American ice sheet melts. This cooler period is called the Younger Dryas 11000 BCE [This is the first text to the left of the dotted curve:] Humans reach Argentina 10500 BCE [An arrow pointing down along the right side of the dotted curve and to the right indicate temperature is increasing again, meaning the dotted curve now moves right to hotter temperatures. This continues until 8000 BCE where it levels out just above 0°C.] Warming resumes Human settlements at Jericho 10000 BCE First development of farming 9500 BCE Saber-toothed cat goes extinct [To the left:] Horses disappear from North America 9000 BCE [To the left, Randall spelled Pokémon wrong:] Last North American Pokemon go extinct [Cueball with a speak and Megan is looking up at this last “fact”.] Megan: That is not a real fact. Temperatures reach modern levels Rising seas cut off the land bridge between North America and Asia Cattle domesticated 8500 BCE Ice sheets retreat across the Canadian border Temperatures start to level out slightly above 1961-1990 levels 8000 BCE [The above sentence breaks over the 8000 BCE line. From here a maximum in temperature on the chart is reached at 0.5°C which will not be overtaken until 2000 CE. It stays almost constant here until 5000 BCE where a slight cooling begins.] 7500 BCE [To the left:] This warm, stable period is called the Holocene Climate Optimum [To the left:] Jiahu settled in China 7000 BCE Final collapse of the North American ice sheet leads to rapid 2-4m sea level rise… [A small arrow points down and left to the right of the dotted curve. There is a small decrease in temperature but it is very small and would have been missed without the arrow and label.] …And a period of cooling in the Northern hemisphere 6500 BCE [To the left:] As seas rise to near their modern levels, Britain is cut off from mainland Europe 6000 BCE Humans develop copper metalworking 5500 BCE [To the left:] Massive volcanic eruption in Oregon creates crater lake Gold metalworking 5000 BCE [To the left:] Invention of the wheel [To the left. To the right of the dotted curve is an arrow pointing down and slightly left. From here temperature decreases very slowly but steadily from 0.5°C until 1000 BCE where a stable plateau is reached around 0°C.] Earth begins to cool slowly mainly due to regular cycles in its orbit 4500 BCE [To the left:] Proto-Indo-European language develops [To the right of the curve Ponytail holds up a hand towards Cueball.] Ponytail: Let’s make our language heavily inflected, so future students have to memorize a zillion verb endings! Cueball: Okay! [To the left:] Permanent settlements in the fertile crescent 4000 BCE Horses domesticated [To the left:] Minoan culture arises on Crete 3500 BCE Egyptian mummification Rise of the Indus Valley civilization [To the left:] Invention of writing in Sumer “prehistory” ends, “history” begins Earliest human whose name we know (Pharaoh Iry-Hor in Egypt) 3000 BCE Three Sovereigns and five emperors period in China Gilgamesh [To the left:] Imhotep Mayan culture emerges [To the left:] Great Pyramid constructed 2500 BCE Corded Ware culture in Europe [To the left of the curve two rock musicians with long hair and electrical guitars are standing on either side of a small gate made of three slabs of stone, one on top of the other two standing stones.] Stonehenge completed Chariots developed 2000 BCE [To the left:] Alphabetic writing developed in Egypt Last mammoths on a tiny Siberian island go extinct [To the left:] Minoan eruption 1500 BCE [To the left:] Iron smelting Olmec civilization develops in Central America [A Trojan horse with two Cueball-like guys in front and a third standing on its back. Its back is at three Cueball’s height and its head rises to the level of the Cueball on its back. It stands on a platform with four wheel on the visible side. There is text on the horse] Setting of the Iliad and the Odyssey Text on horse: Not a trap [To the left:] Invasion of the Sea peoples* * A real thing Polynesians explore the Pacific Ocean 1000 BCE [From 1000 BBC to 1000 CE the temperature is stable and very close to 0°C.] [To the left:] Solomon [Randall spelled Iliad wrongly this time:] Illiad and Odyssey composed [To the left:] Rise of Greek city-states Neo-Assyrian empire [To the left:] First Olympics Zapotec writing in modern Mexico [To the left:] Confucius 500 BCE [To the left:] The stuff in the 300 (film)|movie 300, but regular speed and with more clothing Buddha Nazca Lines [To the left:] Alexander the Great [To the left:] Mayan hieroglyphics Ashoka the Great [To the left:] Paper invented [To the left:] Asterix Teotihuacán metropolis [To the left:] Julius Caesar [At the year 0, there is instead two numbers for each of the two scales before and after Christ:] 1 BCE 1 CE [To the left:] Roman Empire Jesus [To the left and erupting volcano.] Pompeii Three Kingdoms period [To the left:] Gupta empire [To the left:] Various groups take turns sacking Rome [Randall spelled Attila wrong:] Atilla the Hun 500 CE Muhammad [To the left:] Tang Dynasty [An arrow to the right of the dotted curve pointing down, takes a swing far out from the curve and then bends back again. The text label next to it breaks into the next 500 period. The dotted curve stays stable at 0°C along this arrow.] Medieval warm period in Europe and some northern regions (too regional to affect the global average much) [To the left:] Leif Eriksson 1000 CE [The dotted curve moves to the left towards lower temperature reaching a minimum around 1650 of about -0.6°C at the Little Ice Age.] [To the left a drawing of a compass with needle pointing the black end towards north east. There are labels for the four main directions and a label next to it:] N W E S Magnetic compass navigation [To the left:] Ghengis Khan Zheng He’s fleet explores Asia and Africa [To the left:] Aztec Alliance [To the left:] Printing press [To the left:] Columbus 1500 CE European Renaissance [To the left:] Shakespeare 1600 [To the left:] Newton [To the right of the dotted curve there is an arrow pointing down that makes a swing in towards the curve and then back out again. At -0.6°C this is the coldest it has been since 9500 BCE. It is labeled:] ”Little Ice Age” 1700 Steam engines [To the left:] Unites States Independence 1800 Industrial Revolution [To the left:] Telegraphs [After this the dotted curve becomes solid.] 1900 [To the left, and on the line for 1900:] Airplanes [To the left:] World Wars [The solid line takes a step to the right close to 0°C. Over the rest of the 1900s it moves closer to 0°C crossing it before 2000 where it almost reaches the maximum temperature of 0.5 °C from earlier in 8000 BCE.] Fossil fuel CO2 emissions start rapidly increasing [To the left:] Nuclear weapons [To the left:] Internet 2000 Northwest Passage opens [From here to present day the solid line increases rapidly and in 2016 present day is almost reaches 1°C, with about 0.8°C.] 2016 [To the left on the line for 2016:] Present day [From here the curve once again becomes dotted as this is the future. After one dot it splits in two and after the first two dots another split between them occurs forming three possible future dotted curves. The first curve bending down before the others, and thus to the right of the other two reaches about 1.2°C and then goes straight down and stops at the 2100 line. An arrow points to it from the left and a label is written patly before and the rest after the 2100 line to the left of the curve:] Best-case scenario assuming immediate massive action to limit emissions 2100 [The middle curve bends a little down after reaching 1.3°C and then continues this path reaching 2°C in 2100. An arrow point from below to it and a label is written below the curve and below 2100 line:] Optimistic scenario [The last line continues along the path from the last 16 years of the solid line reaching 4.2°C at 2100, almost as far on the other side of 0°C in 150 years as it took 14000 years to move from the other side from the start of the chart. Another arrow point to this from below with a label below the curve and below 2100 line:] Current Path

Ice Age - Definition and Timeline - HISTORY

An ice age is a period in Earth's history when the ice on the polar caps significantly expanded due to an overall lowering of the Earth's global temperatures. During these periods land in North America and Northern Europe were covered by giant ice fields and glaciers.

How do scientists know about ice ages?

Scientists have figured out when past ice ages likely occurred by studying the geology of the land. There are many geological features in Northern Europe and North America that can only be explained by the movements of giant glaciers. Scientists also study the chemicals in rocks and fossil evidence to determine when ice ages have occurred.

Are we living in an ice age?

Yes, you may be surprised to know that we are currently living in an ice age called the Quaternary ice age. The Earth is in a warmer stage of the ice age called an interglacial period.

The 24 Hour Clock Analogy

To help you put the age of the Earth in perspective, this analogy may be helpful. If you think of all of Earth's history as having taken place in just one day, then the pie-chart above is a 24 hour clock. The Earth forms at 12:00 am, and cools down from a molten state over the next several hours. The oceans form and the asteroid bombardment diminishes. Very primitive single celled life appears very quickly, before 4:00 am, and photosynthetic organisms appear before 6:00 am. Right around noon, the atmosphere becomes oxygen rich. By 1:00 pm (13:00 h) the single-celled eukaryotes have arrived. By 5:00 pm (17:00 h) the first multicellular forms appear. The first aquatic animals don't arrive until after 8:00 pm. Plants colonize land at 9:30 pm and land animals follow at 10:00 pm. The dinosaurs are the life of the party for about an hour from 10:40 pm to 11:40 pm. Human ancestors split off from the rest of the hominids at only two minutes to midnight, and modern humans arrive as the clock strikes midnight. You can download this Excel document to see how the chart was made.

If we overlay a 24 hour clock on the history of the Earth, the great span of time becomes easier to comprehend.

A landscape sculpted by ice and water

The Laurentide Ice Sheet and the large volume of meltwater flowing from it greatly altered the landscape of Wisconsin. As a result, the landscape of the area glaciated during the last part of the Wisconsin Glaciation is notably different than that of areas glaciated earlier in the Ice Age (where erosion has destroyed most earlier glacial landforms) and areas that were never glaciated. For example, the outermost limit of the last glacier is marked by a conspicuous ridge of glacially deposited debris. The many lakes and wetlands and the irregular landscape that characterize so many areas of eastern and northern Wisconsin are also a direct result of the last glacier.

Watch the video: Σε Λήθαργο Ο Ήλιος Έρχεται Νέα Εποχή Παγετώνων (December 2021).

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