Cats and Isotopes

A domestic cat in a bag.

A domestic cat in a bag.

Cats. The very mention of them has the power to generate innumerable lazy hits on a blog post. If one were to do an anthropological study of cats using only the Internet as source material, one might be lead to believe that we worship them as deities.

We wouldn’t be the first culture, either. The ancient Egyptians held them in pretty high regard. Their goddess of justice and execution, Mafdet, was a feline-headed creature who protected against snakes and scorpions. Baset, another feline goddess, represented protection, fertility, and motherhood.

Despite the high regard humans have had for cats since at least the dawn of written history, we know very little about how or when they became domesticated. We are pretty sure that the housecat is descended from the African wildcat (Felis silvestris lybica), and people generally assume the process involved a mutually beneficial relationship between farmers and felines in which the cats protected the farmer’s grain from vermin, and the grain provided for a steady supply of vermin for them to eat.

But it is really hard to figure out when that would have happened, and even harder to figure out if that general picture, which makes a great deal of heuristic sense, is accurate.  A recent study on this subject published by a team of archeologists got a great deal of press. They found a small Chinese farming village dated to about 5300 years ago with cat and rodent fossils (among others) discovered at the site.

The basic gist of the study was that chemical analysis of the animal bones found at the site revealed that the rodents ate grain, and that the cats ate those rodents or the grain products directly—suggesting a mutually tolerant relationship between human and cat. Other wild animals found at the site, like deer and hares, didn’t seem to eat any grain, suggesting their food web was independent of any human influence. It’s a fascinating and impressive result, and it seems to be consistent with the generally accepted theory of cat domestication.

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The World’s Longest Conveyor Belt

Satellite image of the Bou Craa conveyor belt

The Bou Craa conveyor belt running through the arid Western Saharan terrain. Credit: Bing maps.

The longest conveyor belt in the world runs 61 miles from the hostile interior of Moroccan occupied Western Sahara to the port city of El-Aaiún. Open to gusty desert winds in many places, the belt’s precious white cargo is strewn across the dusty brown desert, marking  the Earth so profoundly that this massive machine’s outline can be seen from space.

Between around 100 and 55 million years ago, marine waters of the nascent and ever-widening Atlantic Ocean transgressed and regressed over this now dry land. These waters deposited thick muddy sediments containing the decaying tissue, bones, shells, and excrement of dead marine life that had collected and concentrated on the ocean floor over millions of years. As a result, this thick oozing mud, a complex mélange of fetid material, was rich in phosphorus.

Without phosphorus, life itself is not possible. It exists in all living things —in cells, in bones, indeed, even in DNA. For that reason, the mud that formed the hills of Western Sahara so many millions of years ago were full of phosphorus. Now, millions of years later, it is that same phosphorus that we extract from the Earth and load onto a conveyor belt. Read the rest of this entry »

Great Moments in Earth History: Antarctic Glaciation

Buried under thousands of feet of hard, ancient ice lies the solid earth of the Antarctic continent. For some 34 million years, vast glacial plains have ebbed and flowed over this rocky land. But the initiation of Antarctic glaciation—the point in time when conditions became right for snowfall to exceed snowmelt year after year—began suddenly and enigmatically.

satellite imagery of Antarctica

Antarctica today.

The growth of glaciers on Antarctica marks the end of the geologic epoch known as the Eocene—an epoch actually known for some of the hottest global temperatures in Earth’s geologically recent history. High CO2 punctuated by extreme bursts of even more CO2 caused significant warming for the early part of the Eocene’s 22 million year span. Fossil records show that the Antarctic continent was not only ice free then, but that it supported rainforests and crocodiles!

So the transition from a lush tropical landscape to a barren ice covered wasteland is a mystery that scientists have yet to fully explain. Cooling began gradually around the middle Eocene, and it made a pronounced and sudden shift at the Eocene’s conclusion 34 million years ago.

At that time, CO2 levels plummeted. In a geological instant—400,000 years—Antarctica was covered in ice. Some sort of threshold must have been passed, geologists reason. Cooling can beget more cooling because ice reflects incoming heat from the Sun back into space. This undoubtedly happened. But something else had to have occurred to cause the drop in CO2 that allowed the world to become cool enough to form glaciers in the first place.

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Great Moments in Earth History: The Hadean

No complete rocks have survived to tell of the formative years following Earth’s formation some 4.56 billion years ago. The material that would have existed at that time has been broken apart by the power of wind and water. It has melted and metamorphosed under the immense pressure and heat deep within Earth’s interior. It has been recycled back on to the surface. It has existed at every stage of the rock cycle many, many times over.

Despite the thousands of millions of years Earth’s earliest material has encountered, tiny pieces of some of these rocks still exist. Small microscopic grains of a mineral, once part of rocks that would have witnessed Earth as it existed just a couple of hundred million years after its formation, survive to this day.

A black and white image of a zircon crystal

A polished section of the oldest known piece of Earth. Credit: NASA

The oldest known terrestrial material is a single grain of a mineral called zircon which was found in the Jack Hills formation in western Australia. It is 4.4 billion years old. The grain itself was part of a rock composed of the broken and eroded bits of other ancient material that itself has been subject to billions of years of geologic reworking.

Zircon is an extremely rugged mineral made up of silicon and the obscure element zirconium. Its tenacity in the face of time and its ability to provide scientists with enough information to figure out the age when it was formed are among the many reasons it is exciting to geologists. Read the rest of this entry »

Great Moments in Earth History: Colonization of Land by Plants

Up until around 500 million years ago, the continents of Earth were practically lifeless, harboring – at most – slimy mats of bacteria on rocky, barren wastelands. Around this time plants began to creep out of the oceans, gradually developing adaptations that allowed them to expand further and further inland over millions and millions of years. But there is a dark side to this story: the increasing success of plants on land may have contributed to one of the largest set of extinctions known to the fossil record.

An Archaeopteris fossil. These large ferns formed massive forest-like ecosystems in the Devonian.

An Archaeopteris fossil. These large ferns formed massive forest-like ecosystems in the Devonian.

Plants colonized land over a period as long as tens to hundreds of millions of years. But there were a number of evolutionary advances that brought about swift change. Each advance allowed plants to either expand to new habitats or grow larger. And with each advance, the roots of these pioneering plants broke more and more earth apart. To Tom Algeo, a geologist at the University of Cincinnati, this process may have created a chain of events that removed massive quantities of oxygen from the ocean.

Although the first land plants evolved around 500 million years ago, they remained close to the waters edge and did not grow very large for around 100 million years. But these early plants paved the way for the future success of larger plants. This later success is largely due to lignin, tissue that gives plants structure and support.

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Great Moments in Earth History: The Messinian Salinity Crisis and the Zanclean Flood

Author’s note: This post is the first in a series of great Earth history moments. Stay tuned for a new post every other week.

Around 6 million years ago, the Mediterranean Sea became separated from the Atlantic. Cut off from the world’s oceans, it began to evaporate. By 5.3 million years ago, there was literally no sea left. 1000 years later, it was refilled in a geologic instant.

A number of discoveries led to the conclusion that the Mediterranean dried out completely sometime in the past. The first came in the 1960s, when seismic studies of the floor of the Mediterranean revealed a unique layer – dubbed the M reflector – across the whole basin. Scientists interpreted it to be a large layer of salt distributed evenly across the seafloor.

The Glomar Challenger discovered a thick layer of evaporite minerals deep in the Mediterranean seafloor.

The Glomar Challenger discovered a thick layer of evaporite minerals deep in the Mediterranean seafloor. Credit: Ocean Drilling Program, Texas A&M University.

Later, in 1970, a leg of the Deep Sea Drilling Project cored deep into the Mediterranean seabed. They found what the seismic data predicted: a hard layer of evaporites – rocks composed of salts.

The only way to get evaporite rocks at the base of a sea is to evaporate water until it becomes so concentrated with salts that they can no longer be dissolved. This forces them to precipitate into a solid form.

Just as enigmatic as the salt layer, engineers mapping the base of the Nile River in preparation for the construction of the Aswan Dam around this time found that carved deep beneath the silty floor of the Nile was a canyon whose ancient base was well below sea level.

The only way  for a canyon to be carved into bedrock is for a river to flow through it. But a river won’t cut lower than sea level. This deep canyon meant that Medteranian sea level must have been dramatically lower in the past.

In 1972, Kenneth Hsu, the primary investigator on the Deep Sea Drilling Leg that cored the Mediterranean, authored a paper in Nature concluding that the sea must have evaporated nearly completely to produce such an anomalous layer of evaporite minerals and to have cut canyons so deep. In the paper he admitted it was a “preposterous idea,” but stated that no other explanation presented itself. Read the rest of this entry »

Evolution and the Brown Mouse Lemur

The rainforests of Madagascar highlight, with great clarity, the power the physical environment exerts on evolution. As a study abroad student in the fall of 2006, I was researching the sleep habits of the brown mouse lemur in Ranomafana National Park, a protected tract of land in the high rain-forested mountains of Madagascar’s east coast.

During the day, I bushwhacked through this dense rainforest, attempting to locate two or three of these nocturnal mouse lemurs, who had been fixed with tracking collars, as they slept. In the evening, I waited for the lemurs to wake up so that I could record the size and consistency of their sleeping groups.

creative commons: frank vassen

Microcebus rufus, the brown mouse lemur.

One day, as the sun was setting on the bamboo, ferns, and mossy trees of the forest, I watched as multiple lemurs suddenly emerged and attempted to rouse the female lemur I was tracking from her sleep. These lemurs, all male, were attempting to mate with my study subject.

Female brown mouse lemurs, and indeed many species of female lemurs in Madagascar, are only receptive to mating for a very short period of time each year. To make the most of this short mating season, the male lemurs, deathly focused on a single goal, spend the winter months growing testicles that end up being a quarter of their entire body mass. It is no question, given the males’ months of stored hormonal energy, that there would be a significant interest in my study subject that day. Read the rest of this entry »


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