1. Discovering the Atmosphere

2. Where did Earth's Atmosphere come from?

17 September 2003. Ancient Relatives of Algae Yield New Insights into Role of CO2 in Earth's Early Atmosphere. NASA's Earth Observatory. Greenhouse gas has been playing a critical role in warming our planet for billions of years, according to a new study that looks at the photosynthetic cycle by which plants convert light energy and CO2 into cellular tissue.

3. How do Scientists Play the Dating Game?

22 September 1998. How Old are the Rocks? Using Radioactivity to Find Out. When a volcanic magma cools down and solidifies, radioactive "clocks" in it can be set. Geologists can use these "clocks" to find out how long ago the rock formed.

4. The Beginning of Life on Earth

Archive of Past Articles for Chapter 4

2008 December 8. Meteor impacts may have sparked life on Earth. By Emma Young, New Scientist. Excerpt: While space rocks hurtling in from space threaten to deal modern life a mortal blow, meteorite impacts during Earth's early history may have played a pivotal role in kick-starting life on the planet.
Exactly how and when organic molecules appeared in abundance on the young Earth, leading to the origin of life about 4 billion years ago, has been unclear. But new research suggests that meteor impacts could have created amino acids, the building blocks of life.
Yoshihiro Furukawa at Tohoku University in Sendai, Japan, and colleagues used a high-velocity propellant gun to simulate the impacts of ordinary carbon-containing chondrite meteorites - the most common type of meteorite - into the early ocean. Afterwards, they recovered a variety of organic molecules, including fatty acids, amines, and an amino acid.
Oceans began to form about 4.3 billion years ago, when meteorites were hitting Earth about 1000 times more frequently than they do today, says Furukawa. "This study is the first to show that an amino acid can be synthesised by a naturally possible mechanism on the early Earth," he says....

2008 October 16. Volcanoes May Have Provided Sparks and Chemistry for First Life. NASA Earth Observatory. Excerpt: Lightning and gases from volcanic eruptions could have given rise to the first life on Earth, according to a new analysis of samples from a classic origin-of-life experiment by NASA and university researchers....
...From 1953 to 1954, Professor Stanley Miller, then at the University of Chicago, performed a series of experiments with a system of closed flasks containing water and a gas of simple molecules. At the time, the molecules used in the experiment (hydrogen, methane, and ammonia) were thought to be common in Earth's ancient atmosphere.
The gas was zapped with an electric spark. After running the experiment for a few weeks, the water turned brown. When Miller analyzed the water, he found it contained amino acids, which are the building blocks of proteins -- life's toolkit... The spark provided the energy for the molecules to recombine into amino acids, which rained out into the water....
...Professor Jeffrey Bada, a co-author of the paper, was [Miller's] graduate student in chemistry between 1965 and 1968....
"...When Adam and I found the samples from the original experiments, it was a great opportunity to reanalyze these historic samples using modern methods," said Bada. The team wanted to see if modern equipment could discover chemicals that could not be detected with the techniques of the 1950s. They analyzed the samples and turned to Daniel Glavin and Jason Dworkin of NASA's Goddard Space Flight Center in Greenbelt, Md....
..."We discovered 22 amino acids, 10 of which have never been found in any other experiment like this," said Glavin. This is significant because thinking on the composition of Earth's early atmosphere has changed. Instead of being heavily laden with hydrogen, methane, and ammonia, many scientists now believe Earth's ancient atmosphere was mostly carbon dioxide, carbon monoxide, and nitrogen....

2006 June 6. STUDY SHOWS OUR ANCESTORS SURVIVED 'SNOWBALL EARTH' - Earth Observatory. Excerpt: It has been 2.3 billion years since Earth's atmosphere became infused with enough oxygen to support life as we know it. About the same time, the planet became encased in ice that some scientists speculate was more than a half-mile deep. That raises questions about whether complex life could have existed before "Snowball Earth" and survived, or if it first evolved when the snowball began to melt. New research shows organisms called eukaryotes -- organisms of one or more complex cells that engage in sexual reproduction and are ancestors of the animal and plant species present today -- existed 50 million to 100 million years before that ice age and somehow did survive. The work also shows that the cyanobacteria, or blue-green bacteria, that put the oxygen in the atmosphere in the first place, apparently were pumping out oxygen for millions of years before that, and also survived Earth's glaciation. The findings call into question the direst models of just how deep the deep freeze was, said University of Washington astrobiologist Roger Buick, a professor of Earth and space sciences. While the ice likely was widespread, it probably was not consistently as thick as a half-mile, he said. "That kind of ice coverage chokes off photosynthesis, so there's no food for anything, particularly eukaryotes. They just couldn't survive," he said. "But this research shows they did survive."

Archive of Past Articles for Chapter 4

5. The Origin of Our Oxygen-Rich Atmosphere

27 September 2007 NASA RELEASE: 07-215 - NASA RESEARCH INDICATES OXYGEN ON EARTH 2.5 BILLION YEARS AGO. Excerpt: MOFFETT FIELD, Ca lif. - NASA-funded astrobiologists have found evidence of oxygen present in Earth's atmosphere earlier than previously known, pushing back the timeline for the rise of oxygen in the atmosphere. Two teams of researchers report that traces of oxygen appeared in Earth's atmosphere from 50 to 100 million years before what is known as the Great Oxidation Event. This event happened between 2.3 and 2.4 billion years ago, when many scientists think atmospheric oxygen increased significantly from the existing very low levels.
Scientists analyzed a kilometer-long drill core from Western Australia, representing the time just before the major rise of atmospheric oxygen. They found evidence that a small but significant amount of oxygen was present in Earth's oceans and atmosphere 2.5 billion years ago. The findings appear in a pair of research papers in the Sept. 28 issue of the journal Science.
"We seem to have captured a piece of time during which the amount of oxygen was actually changing -- caught in the act, as it were," said Ariel Anbar, an associate professor at Arizona State University, Tempe, and leader of one of the research teams.
...One possible explanation for the Great Oxidation Event is the ancient ancestors of today's plants first began to produce oxygen by photosynthesis. However, many geoscientists think organisms began to produce oxygen much earlier, but the oxygen was destroyed in reactions with volcanic gases and rocks.
..."What we have now is new evidence for some oxygen in the environment 50 to 100 million years before the big rise of oxygen," Anbar said. "Our findings strengthen the notion that organisms learned to produce oxygen long before the Great Oxidation Event, and that the rise of oxygen in the atmosphere ultimately was controlled by geological processes."
...For more information about the NASA Astrobiology Institute, visit:
http://nai.nasa.gov

3 February 2004. When Giants Had Wings and 6 Legs. By HENRY FOUNTAIN, New York Times. Before the dinosaurs, it was the insects that were huge. Why? It may have been the air.... There was an array of giant flightless insects, and a five-foot-long millipede-like creature, Arthropleura, that resembled a tire tread rolled out flat. But perhaps the most remarkable of all were the giant dragonflies, Meganeuropsis permiana and its cousins, with wingspans that reached two and a half feet. They were the largest insects that ever lived. These large species thrived about 300 million years ago, when much of the land was lush and tropical and there was an explosion of vascular plants (which later formed coal, which is why the period is called the Carboniferous). But the giant species were gone by the middle to late Permian, some 50 million years later. Scientists have long suspected that atmospheric oxygen played a central role in both the rise and fall of these organisms. Recent research on the ancient climate by Dr. Robert A. Berner, a Yale geologist, and others reinforces the idea of a rise in oxygen concentration - to about 35 percent, compared with 21 percent now - during the Carboniferous. Because of the way many arthropods get their oxygen, directly through tiny air tubes that branch through their tissues rather than indirectly through blood, higher levels of the gas might have allowed bigger bugs to evolve.... "It's been out there in the literature for a long time without a causal mechanism," said Dr. Robert Dudley, a professor at the University of California at Berkeley who has studied the effects of elevated oxygen pressures on modern insects. ...Dr. Jon F. Harrison, a professor at Arizona State ... said, "It's still in the realm of speculation."

6. How and When did Complex Life Begin?

7. Earth's Shifting Crust

2008 May.The Living Story of Sulawesi. by Kathleen M. Wong, ScienceMatters@Berkeley. Excerpt: The Indonesian island of Sulawesi is a 12,000-square-mile jigsaw puzzle. During the past 25 million years, drifting tectonic plates tore four separate paleo-islands from the far corners of the South Pacific and smashed them together in a steamy corner of Southeast Asia.
This turbulent history has turned Sulawesi into a complex biological cipher. Today, it houses a mélange of species with confusing origins: some may have been passengers on the original islands, some may have arrived afterward, and some may have evolved from the mix.
...Jim McGuire, curator of herpetology at Berkeley's Museum of Vertebrate Zoology and a professor of integrative biology, is studying how these species evolved and came to be distributed on Sulawesi today.
.."It was as if they were cut off from each other at some point. But in many cases we don't know what the underlying mechanism would be," McGuire says.
...Based on these data, he uses computer simulations to reconstruct the evolutionary history of these animal groups. He then plans to go back and study contact zones between species more closely to try to identify any environmental or ecological barriers, such as past flooding or the presence of a predator, that are enforcing species isolation....

28 August 2007. A Daddy Longlegs Tells the Story of the Continents' Big Shifts. By CARL ZIMMER, NY Times. Excerpt: Few people have heard of the mite harvestman, .... The animal is a relative of the far more familiar daddy longlegs. But its legs are stubby rather than long, and its body is only as big as a sesame seed. ... "They look like grains of dirt," said Gonzalo Giribet, an invertebrate biologist at Harvard. ... Dr. Giribet and his colleagues have spent six years searching for them on five continents. The animals have an extraordinary story to tell: they carry a record of hundreds of millions of years of geological history, chronicling the journeys that continents have made around the Earth.
The Earth's land masses have slowly collided and broken apart again several times, carrying animals and plants with them. These species have provided clues to the continents' paths.
The notion of continent drift originally came from such clues. In 1911, the German scientist Alfred Wegner was struck by the fact that fossils of similar animals and plants could be found on either side of the Atlantic. The ocean was too far for the species to have traveled themselves. Wegner speculated - correctly, as it turned out - that the surrounding continents had originally been welded together in a single landmass, which he called Pangea.
Continental drift, or plate tectonics as it is scientifically known, helped move species around the world. Armadillos and their relatives are found in South America and Africa today because their ancestors evolved when the continents were joined. ...The 5,000 or so mite harvestmen species can be found on every continent except Antarctica. Unlike animals found around the world like cockroaches, mite harvestmen cannot disperse well. The typical harvestman species has a range of less than 50 miles. Harvestman are not found on young islands like Hawaii.
"It's really hard to find a group of species that is distributed all over the world but that also don't disperse very far," said Sarah Boyer, a former student of Dr. Giribet, now an assistant professor at Macalester College in St. Paul...

8. Highs and Lows over the Past 750 Million Years

Archive of Past Articles for Chapter 8

14 November 2006. Paleoclimatology: Understanding the Past to Predict the Future. By Holli Riebeek. Scientists use complicated climate models to predict how Earth's climate might change in the future. One of the best ways to test the reliability of such models is to see how well they recreate climates of the past.

7 November 2006 In Ancient Fossils, Seeds of a New Debate on Warming. By WILLIAM J. BROAD. NY Times. Excerpt: In recent years, scientists have learned about the changing makeup of the vanished gases by teasing subtle clues from fossilized soils, plants and sea creatures. They have also gained information from computer models that predict how phenomena like eroding rocks and erupting volcanoes have altered the planet's evolving air. "It's getting a lot more attention," Michael C. MacCracken, chief scientist of the Climate Institute, a research group in Washington, said of the growing field. For the first time, the Intergovernmental Panel on Climate Change, a United Nations group that analyzes global warming, plans to include a chapter on the reconstructions in its latest report, due early next year.The discoveries have stirred a little-known dispute that, if resolved, could have major implications. One side foresees a looming crisis of planetary heating; the other, temperature increases that would be more nuisance than catastrophe. Some argue that CO2 fluctuations over the Phanerozoic follow climate trends fairly well, supporting a causal relationship between high gas levels and high temperatures. Other experts say that the fluctuations in the gas levels often fall out of step with the planet's hot and cold cycles, undermining the claimed supremacy of carbon dioxide. Highlighting the gap, the two sides clash on how much the Earth would warm today if carbon dioxide concentrations double from preindustrial levels, as scientists expect. Many climatologists see an increase of as much as 8 degrees Fahrenheit. Carbon dioxide skeptics and others see the reconstructions of the last 15 years as increasingly reliable, posing fundamental questions about the claimed powers of carbon dioxide. "Some of the work has been quite meticulous," Thure E. Cerling, an expert at the University of Utah on Phanerozoic climates, said. "We are likely to learn something."

Archive of Past Articles for Chapter 8

9. What Happened to the Dinosaurs?

Archive of Past Articles for Chapter 9

2008 December 15. Fight over dinosaur death flares anew in S.F. By David Perlman, San Francisco Chronicle. Excerpt: SAN FRANCISCO -- The age of the dinosaurs ended abruptly about 65 million years ago when some catastrophic event drove them to extinction, and now a vehement controversy over their disappearance is emerging anew.
...An international group of scientists is arguing that poisonous fumes from violent waves of volcanic eruptions in India millions of years ago killed off the beasts, not - as UC Berkeley scientists first proposed nearly 30 years ago - the impact of a giant meteorite that blasted a huge undersea crater in Mexico and touched off a kind of "nuclear winter" that darkened the skies with a pall of dust and debris that the creatures could not possibly have survived.
The origins of the big debate began nearly 30 years ago when the geologist Walter Alvarez at UC Berkeley and his father, Luis, a Nobel physics laureate, proposed that a cosmic collision by an object from space at least six miles wide crashed just off Mexico's Yucatan peninsula about 65 million years ago and created what is known as the Chicxulub crater.
...Gerta Keller of Princeton University..., joined by Vincent Courtillot of the University of Paris and Sunil Bajpai, of the Indian Institute of Technology, ...insisted that the impact crater was formed at least 300,000 years before the great extinction and "caused no species extinctions" - certainly not to the dinosaurs. She came to her conclusion, in part, by age-dating clusters of mineral spherules that presumably spewed out of the Chicxulub crater and landed in Texas, where Keller said she gathered and tested them.
Instead, she argued, the extinction coincided with three or four waves of volcanism in a region of northwest India known as the Deccan traps....
...Walter Alvarez...rejected the idea that volcanism in India was the sole cause of the mass extinction.
..."Few experts on the mass extinction would agree with Keller that the Chicxulub impact is older than the mass extinction," he said....

2008 Mar 25. Theory on Dinosaurs and Volcanic Activity 65 Million Years Ago. By HENRY FOUNTAIN, NY Times. Excerpt: An asteroid or comet impact gets most of the credit for the event that wiped out the dinosaurs 65 million years ago. But massive volcanic activity around the same time might have played a role, too, by pumping enormous amounts of gases containing sulfur and chlorine into the atmosphere. An analysis by Stephen Self of the Open University in Milton Keynes, England, and colleagues lends new support to that idea. By looking at tiny bits of glass that formed inside the lava flows, they've been able to reconstruct how much sulfur and chlorine were released. The volcanic activity over thousands of years produced a flood of lava, now known as the Deccan Trapps, that is thousands of feet thick over thousands of square miles of central India. The researchers' analysis, reported in Science, suggests the eruption could have produced ...on an annual basis, ...the amount of SO2 ... at least 10 times greater than the current amount released by worldwide volcanic activity. The environmental impact of that much gas, they add, was probably severe.

6 November 2007. Rethinking What Caused the Last Mass Extinction. By JOHN NOBLE WILFORD. NY Times. Excerpt: FREEHOLD, N.J. - Splashing through a shallow creek in suburban New Jersey, the paleontologists stepped back 65 million years to the time of the last mass extinction, the one notable for the demise of the dinosaurs. ...At the time, sea levels were higher and New Jersey was warmer. The proto-Atlantic waters reached the center of the current boundaries of New Jersey, standing more than 60 feet deep here, where on a recent day the paleontologists were up to their ankles in a creek. They had their eyes on the sediments in the bank just above the iridium clay. They call this the Pinna layer.
On previous visits, they had found in the Pinna rock and soil a surprising number of marine fossils, including small clams, crabs and sea urchins. There was an abundance of ammonites, considered index organisms of the uppermost Cretaceous environment. Somehow, here at least, life appeared to have not only persisted but also flourished for tens, perhaps hundreds, of years after the putative asteroid impact.
..."It is undeniable that the iridium spike at the base of the Pinna layer was produced by the impact," Dr. Landman said. "That's amazing and makes it hard to explain the ammonite abundances we find above the iridium anomaly."
Gerta Keller, a paleontologist and professor of geosciences at Princeton University, said the research by Dr. Landman's group "shows the complexity of this extinction event and the difficulty explaining it by the currently popular impact theory."....

28 November 2006. New York Times. Marine Life Leaped From Simple to Complex After Greatest Mass Extinction. By Andrew C. Revkin. Excerpt: At least five mass extinctions, most presumably caused by asteroids that struck the earth, have transformed global ecology in the half-billion years since the emergence of multicelled life, lopping entire branches from the evolutionary tree and causing others to flourish. The greatest "great dying," 251 million years ago, erased 95 percent of species in the oceans (and most vertebrates on land). But new research suggests that it was followed by an explosion of complexity in marine life, one that has persisted ever since. Moreover, it happened quite suddenly... The shift to complicated, interrelated ecosystems was more like a flip of a switch than a slow trend. The researchers detected the change by analyzing records of marine fossils from 1,176 sites around the world, which are part of a new international archive, the Paleobiology Database (pbdb.org).

23 September 2006. DINOSAURS' CLIMATE SHIFTED TOO, REPORT SHOWS. Ancient rocks suggest dramatic climate changes during the dinosaur-dominated Mesozoic Era, a time once thought to have been hot and humid. NASA Earth Observatory.

Archive of Past Articles for Chapter 9

10. The Ice Ages

Archive of Past Articles for Chapter 10

23 March 2007. MICROFOSSILS UNRAVEL CLIMATE HISTORY OF TROPICAL AFRICA. Earth Observatory News. Scientists from the Royal Netherlands Institute for Sea Research obtained for the first time a detailed temperature record for tropical central Africa over the past 25,000 years. ... a marine sediment core taken in the outflow of the Congo River... contained eroded land material and microfossils from marine algae. The results show that the land environment of tropical Africa was cooled more than the adjacent Atlantic Ocean during the last ice-age. This large temperature difference between land and ocean surface resulted in drier conditions compared to the current situation, which favors the growth of a lush rainforest. These findings provide further insight in natural variations in climate and the possible consequences of a warming earth on precipitation in central Africa. The results will be published in this week's issue of Science. ...ocean surface and land temperatures behaved differently during the past 25,000 years. During the last ice age, temperatures over tropical Africa were 21¡C, or about 4¡C lower than today, whereas the tropical Atlantic Ocean was only about 2.5¡C colder. By comparing this temperature difference with existing records of continental rainfall variability, lead author Johan Weijers and his colleagues concluded that the land-sea temperature difference has by far the largest influence on continental rainfall. This can be explained by the strong relationship of air pressure to temperature. When the temperature of the sea surface is higher than that of the continent, stronger offshore winds reduce the flow of moist sea air onto the African continent. This occurred during the last ice age and, as a consequence, the land climate in tropical Africa was drier than it is in today's world, where it favours the growth of a lush rainforest.

8 June 2006. NEW STUDY SHOWS MUCH OF THE WORLD EMERGED FROM LAST ICE AGE TOGETHER - Earth Observatory. Excerpt: The end of the recurring, 100,000-year glacial cycles is one of the most prominent and readily identifiable features in records of the Earth's recent climate history. Yet one of the most puzzling questions in climate science has been why different parts of the world, most notably Greenland, appear to have warmed at different times and at different rates after the end of the last Ice Age. However, a new study appearing in the upcoming issue of the journal Science suggests that, except for regions of the North Atlantic, most of the Earth did, in fact, begin warming at the same time roughly 17,500 years ago. In addition, scientists suggest that ice core records from Greenland, which show that average temperatures there did not warm appreciably until about 15,000 years ago, may have remained in a hyper-cold state largely as a result of events triggered by warming elsewhere....

Archive of Past Articles for Chapter 10

11. Climate and Human Evolution

Archive of Past Articles for Chapter 11

2008 November 27. Did Neanderthal cells cook as the climate warmed? By Ewen Callaway, New Scientist. Excerpt: Neanderthals may have gone extinct because their cells couldn't cope with climate change, according to a new hypothesis...
Metabolic adaptations to Ice Age Europe may have proved costly to Neanderthals after the continent's climate started to change, says Patrick Chinnery, a molecular biologist at Newcastle University, UK.
He and colleague Gavin Hudson identified potentially harmful mutations in the newly sequenced Neanderthal mitochondrial genome. In particular, the researchers found genes that are associated with neurodegenerative diseases and deafness. "If they were found in modern humans they would be bad news," Chinnery says.
The extinction of Neanderthals, close relatives of modern humans, some 25,000 years ago remains unexplained.
...Chinnery and Hudson suggest that mutations in mitochondria helped Neanderthals cope with the cold weather, but that when the climate started fluctuating between warm and cold periods, they were at a disadvantage.
In all cells, from yeast to human, a mitochondrion's main job is to produce the energy that powers cells... Our mitochondria do this quite efficiently under ideal conditions...
Mutations that sap this efficiency would generate heat instead - a potentially useful trick for Neanderthals who are known to have had adaptations to cold weather, Chinnery says. However, a warmer and less climatically stable habitat could have spelled trouble for Neanderthals with such mutations....

2008 August 14. Graves Found From Sahara’s Green Period. By JOHN NOBLE WILFORD, The New York Times. Excerpt: When Paul C. Sereno went hunting for dinosaur bones in the Sahara, his career took a sharp turn from paleontology to archaeology. The expedition found what has proved to be the largest known graveyard of Stone Age people who lived there when the desert was green.
The first traces of pottery, stone tools and human skeletons were discovered eight years ago at a site in the southern Sahara, in Niger. After preliminary research, Dr. Sereno, a University of Chicago scientist who had previously uncovered remains of the dinosaur Nigersaurus there, organized an international team of archaeologists to investigate what had been a lakeside hunting and fishing settlement for the better part of 5,000 years, originating some 10,000 years ago.
...the team described finding about 200 graves belonging to two successive populations. Some burials were accompanied by pottery and ivory ornaments....
...The sun-baked dunes at the site, known as Gobero, preserve the earliest and largest Stone Age cemetery in the Sahara, Dr. Sereno’s group reported...
Other scientists said the discovery appeared to provide spectacular evidence that nothing, not even the arid expanse of the Sahara, was changeless. About 100 million years ago, this land was forested and occupied by dinosaurs and enormous crocodiles. Around 50,000 years ago, people moved in and left stone tools and mounds of shells, fish bones and other refuse. The lakes dried up in the last Ice Age.
Then the rains and lakes of a fecund Sahara returned about 12,000 years ago, and remained, except for one 1,000-year interval, until about 4,500 years ago. Geologists have long known that the region’s basins retained mineral residue of former lakes, and other explorers have found scatterings of human artifacts from that time, as Dr. Sereno did at Gobero in 2000.
“Everywhere you turned, there were bones belonging to animals that don’t live in the desert,” he said. “I realized we were in the green Sahara.”...

2008 May 9. How the Sahara Became Dry & Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years. Jonathan A. Holmes. Science 9 May 2008: Vol. 320. no. 5877, pp. 752 - 753 DOI: 10.1126/science.1158105. Excerpt: Around 14,800 years ago, a strengthening of the summer monsoons led to a dramatic increase in North African lakes and wetlands and an extension of grassland and shrubland into areas that are now desert, creating a "green Sahara" (see the first figure). ...a lake sediment record ... sheds light on how this "African Humid Period" came to an end.

2008 May 9. Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years. S. Kropelin, et al. Science: Vol. 320. no. 5877, pp. 765 - 768 DOI: 10.1126/science.1154913. Excerpt: Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural archives recording its transition from a "green Sahara" to the present hyperarid desert. Our continuous 6000-year paleoenvironmental reconstruction from northern Chad shows progressive drying of the regional terrestrial ecosystem in response to weakening insolation forcing of the African monsoon and abrupt hydrological change in the local aquatic ecosystem controlled by site-specific thresholds. Strong reductions in tropical trees and then Sahelian grassland cover allowed large-scale dust mobilization from 4300 calendar years before the present (cal yr B.P.). Today's desert ecosystem and regional wind regime were established around 2700 cal yr B.P. This gradual rather than abrupt termination of the African Humid Period in the eastern Sahara suggests a relatively weak biogeophysical feedback on climate. ...One of the most prominent environmental changes of the past 10,000 years is the transition of northern Africa from a "green Sahara" during the early Holocene "African Humid Period" to the world'slargest warm desert today. Detailed knowledge of the tempo and mode of this transition is crucial for understanding the interaction between tropical and mid-latitude weather systems and the multiple impacts of mineral aerosols exported from the Sahara on global climate and distant ecosystems....

13 November 2007. Jawbone Sheds Light on Divergence of Humans and Apes. By HENRY FOUNTAIN, NY Times. Excerpt: Scientists who study the divergence of humans from the other great apes have been stymied by a lack of evidence. It is thought that humans and chimpanzees split 6 million to 7 million years ago, and humans and gorillas a couple of million years before that. But almost no ape fossils from this period - the Late Miocene - have been found in Africa.
So some scientists suggest that an interloper of sorts, an ancient ape from Eurasia, returned 10 or 11 million years ago to Africa and became the last common ancestor of humans and the African great apes.
The discovery of a 10-million-year-old jawbone with teeth, in deposits of volcanic mud in Nakali, Kenya, may help put such thoughts to rest.
Yutaka Kunimatsu of Kyoto University in Japan and colleagues report in The Proceedings of the National Academy of Sciences that the fossil, the first of such vintage to be found in the region since 1982, represents a new genus of great ape....

2 October 2007. Fossil DNA Expands Neanderthal Range. By NICHOLAS WADE. NY Times. Excerpt:
In the Treaty of Tordesillas, Spain and Portugal divided the world outside Europe between them. That was not the first time that two rival groups carved up the globe. More than 50,000 years ago, all the world outside Africa was divided between two archaic human species.
The Neanderthals held sway in Europe and the Near East, bottling up the troublesome ancestors of modern humans in Africa, and Homo erectus dominated East Asia. But a new discovery suggests that this division of the world may not have been quite so clear-cut.
...Svante Paabo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany... has shown that Neanderthal DNA can be picked out and identified. So far, he and others have identified DNA from 13 European Neanderthals.
He and colleagues have now identified Neanderthal mitochondrial DNA in bones at two new sites, they say in an article published electronically in Nature this week. One is Teshik Tash, in Uzbekistan, some 750 miles east of the Caspian Sea and, until now, the easternmost known limit of Neanderthal territory. The other bones are from the Okladnikov cave in the Altai mountains, some 1,250 miles farther east.
This huge extension of the Neanderthal's known range puts them well into southern Siberia.
Because the mitochondrial DNA sequence of the new finds differs only slightly from that of the European Neanderthals, Dr. Paabo believes that they may have moved into Siberia relatively late in the Neanderthal period, perhaps as recently as 127,000 years ago, when a warm period made Siberia more accessible.
If Neanderthals penetrated as far as Siberia, might they have reached ever farther east, trespassing far into the assumed domain of Homo erectus? "We now know that they are on the doorstep to Mongolia and even China, so I would not be surprised if we one day find a Marco Polo Neanderthal," ....

26 June 2007. Humans Have Spread Globally, and Evolved Locally. The New York Times. By NICHOLAS WADE. Excerpt: Historians often assume that they need pay no attention to human evolution because the process ground to a halt in the distant past. That assumption is looking less and less secure in light of new findings based on decoding human DNA. People have continued to evolve since leaving the ancestral homeland in northeastern Africa some 50,000 years ago, both through the random process known as genetic drift and through natural selection. A striking feature of many of these changes is that they are local. The genes under selective pressure found in one continent-based population or race are mostly different from those that occur in the others. These genes so far make up a small fraction of all human genes. The new scans for selection show so far that the populations on each continent have evolved independently in some ways as they responded to local climates, diseases and, perhaps, behavioral situations. The concept of race as having a biological basis is controversial, and most geneticists are reluctant to describe it that way. But some say the genetic clustering into continent-based groups does correspond roughly to the popular conception of racial groups.

21 September 2006. Little Girl, 3 Million Years Old, Offers New Hints on Evolution. By JOHN NOBLE WILFORD. NY Times. Excerpt: If the fossil Lucy, the most famous woman from out of the deep human past, had a child, it might have looked a lot like the bundle of skull and bones uncovered by scientists digging in the badlands of Ethiopia. The paleontologists who are announcing the discovery in the journal Nature today said the 3.3-million-year-old fossils were of the earliest well-preserved child ever found in the human lineage. It was ... a member of the Australopithecus afarensis species, the same as Lucy's.
An analysis of the skeleton revealed evidence of a species in transition, ...afarensis walked upright, like modern humans. But gorillalike arms and shoulders suggested that it possibly retained an ancestral ability to climb and swing through the trees. ...The Dikika girl's brain size ...was about the same as that of a similarly aged chimpanzee, but a comparison with adult afarensis skulls indicates a relatively slow brain growth slightly closer to that of humans. ...hyoid bone ...a rarely preserved bone in the larynx, or voice box, that supports muscles of the throat and tongue. ... appeared to be primitive and more similar to those found in apes than in humans, the scientists said, but is the first hyoid found in such an early human-related species and thus important in research about the origins of human speech.
The first relatively complete shoulder blades to be found in an australopithecine individual was one of the most puzzling aspects of the discovery, several scientists said. The lower body appeared to be adapted for upright walking by afarensis. But the shoulders and long arms were more apelike.

Archive of Past Articles for Chapter 11

12. Climate and Culture

2008 November 7. Rise and Fall of Chinese Dynasties Tied to Changes in Rainfall. By David Biello, Scientific American. Excerpt: In the late ninth century a disastrous harvest precipitated by drought brought famine to China under the rule of the Tang dynasty. By A.D. 907—after nearly three centuries of rule—the dynasty fell when its emperor, Ai, was deposed, and the empire was divided. According to the atmospheric record contained in a stalagmite, one of the causes of that downfall may have been climate change.
"We think that climate played an important role in Chinese history," says paleoclimatologist Hai Cheng of the University of Minnesota, a member of the scientific team that harvested and analyzed the stalagmite from Wanxiang Cave in Gansu Province in northwest China. The stalagmite reveals, for example, that the vital rains of the Asian monsoon weakened at the time of the downfalls of the Tang, Yuan and Ming dynasties over the past 1,810 years.
...Composed of calcium carbonate leached from dripping water, the 4.6-inch- (11.7-centimeter-) long stalagmite preserves a record of rainfall in this region, which is on the edge of the area impacted by the Asian monsoon. The region gets less rainfall when the monsoon is mild and more when it is strong...
These periods of strong and weak rains, when compared with Chinese historical records, coincide with periods of imperial turmoil or prosperity....
In fact, the collapse of the Tang Dynasty coincides with that of the Mayan civilization—both due to extreme drought. "We have demonstrated that the cave record correlates well with many other records, including the Little Ice Age in Europe, temperature changes [across the] Northern Hemisphere, and major solar variability," Cheng notes....

2008 August 31. For the first time in human history, the North Pole can be circumnavigated. By Geoffrey Lean, The Independent. Excerpt: Open water now stretches all the way round the Arctic, making it possible for the first time in human history to circumnavigate the North Pole... New satellite images, taken only two days ago, show that melting ice last week opened up both the fabled North-west and North-east passages, in the most important geographical landmark to date to signal the unexpectedly rapid progress of global warming.
Last night Professor Mark Serreze, a sea ice specialist at the official US National Snow and Ice Data Center (NSIDC), hailed the publication of the images...as "a historic event", and said that it provided further evidence that the Arctic icecap may now have entered a "death spiral". Some scientists predict that it could vanish altogether in summer within five years, a process that would, in itself, greatly accelerate.
...scientists...have long regarded the disappearance of the icecap as inevitable as global warming takes hold, though until recently it was not expected until around 2070.
Many scientists now predict that the Arctic ocean will be ice-free in summer by 2030 – and a landmark study this year by Professor Wieslaw Maslowski at the Naval Postgraduate School in Monterey, California, concluded that there will be no ice between mid-July and mid-September as early as 2013....

Summer 2007. Forest Magazine. Thirsting for Water. By Allen Best. Excerpt: ...The dust traveled far, even to New York City. In Kansas, Oklahoma, Texas and Colorado, where the Dust Bowl was most severe, the roiling clouds were deadly. The young and old, even the formerly robust, succumbed to pneumonia. The luckier ones, the quitters, abandoned the dryland farms ... and migrated westward, ....
Several decades of wet weather had supported the widespread plowing of grasslands in a semi-arid climate. Then came drought, lasting the better part of the decade. In all, about a third of a million people left the Great Plains. It was, until Hurricane Katrina, the greatest population displacement in the United States caused by an environmental event.
The Dust Bowl, say climatologists, is unlikely to occur again.
Farmers and government scientists learned much from the experience about how to farm the land-and where not to. But drought most certainly will return, perhaps even more harshly. And turning to the American Southwest, ...experts say new evidence reveals a clearer picture of extended and sometimes severe droughts in the past 1,100 years that very well may reappear-this time with an overlay of hotter temperatures caused by increased levels of greenhouse gases. What effect these human-caused emissions will have on precipitation is still uncertain. On the matter of temperature, however, nearly all the computer models reach one conclusion: It will get hotter, much hotter, in places like Tucson, Colorado Springs and Reno. And hotter-even if precipitation stays the same-means drier. In other words, the "average" of the future will resemble what in the past we called drought.
...WHAT THE TREES SAY
...Climates of the past can be documented in various ways, but one of the most important methods is by studying tree rings, a scientific discipline called dendrochronology. ...
What these tree rings say is that the Southwest was far more arid in the past. ... A period from 800 to 1300 A.D. was generally more arid and punctuated by what paleoclimatologists call megadroughts. Some lasted thirty years. Archaeologists think that one of the final megadroughts, from about 1270 to 1300, may have partly caused the Ancestral Pueblo (also called the Anasazi) to vacate their cliff-dwelling communities at Mesa Verde in Colorado and Chaco Canyon in Arizona.....

13. What does Earth's Past Tell us about Our Future?

Archive of Past Articles for Chapter 13

February 2006. Affecting Evolution and Extinction. By David Pescovitz. ScienceMatters@Berkeley, Volume 3, Issue 18. Every so often, a huge number of species on Earth are wiped out relatively quickly. The last time a large extinction event occurred, between 50,000 and 10,000 years ago, two-thirds of large mammals were swept into the dustbin of history. Why? UC Berkeley paleontologist Anthony Barnosky sifts through the fossil record to understand how environmental changes can cause mammals to move, evolve, and sometimes die off. His research could even help reveal whether we're headed for another mass extinction. ...The aim... is to differentiate between effects of climate change that are natural, and those that could be harbingers of a bigger problem.... "Is part of being a species the fact that you move around in response to climate change and it's no big deal?" Barnosky says. "I'm trying to establish a natural baseline of how much communities change in response to climate change in the past." ... Barnosky ... investigate[d] the cause of large mammal extinctions in the late Pleistocene period, 50,000 to 10,000 years ago. Historically, scientists have thought that human populations of the time over-hunted, killing off animals such as mammoths, ground sloths, native American horses, and camels. However, Barnosky and his colleagues discovered that human impact wasn't the sole cause of the extinctions. Rather, climate change combined with the over-hunting was a "one-two punch" leading to the extinction, he says. The big concern, Barnosky says, is that the state of the planet then is not so different from today. "We've ramped everything up," he says. "Global warming has never been faster and human populations are exploding exponentially. Realistically, I think the ecosystem will change pretty dramatically.

Archive of Past Articles for Chapter 13

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