Sunday, June 26, 2011

Mr. Bones

Tyrannosaurus rex on display at the American Museum of Natural History.

Barnum Brown was arguably the greatest fossil hunter of all time. Working for the American Museum of Natural History in New York, he had a career spanning more than 60 years. The museum boasts the largest collection of fossil dinosaurs in the world, thanks in large part to Brown’s collection efforts. Mr. Bones, as he was affectionately known by admirers, had his discoveries plastered on the front page of newspapers across the country and had been on so many radio programs and given so many lectures that he was considered one of the most famous scientists in the world during the first half of the twentieth century.
  Brown was completely dedicated to his work with the museum. One chilly December morning in 1898, Brown arrived at the museum as usual and by the time he had removed his coat he was called into Professor Osborn’s office. Osborn was the curator of vertebrate paleontology for the museum and wanted to send Brown on an expedition to Patagonia. Brown’s account from his journal follows: “Yesterday, about three hours before the Capac was to sail I was notified by Professor Osborn that arrangements had been made for me to go to South America. Four of the Dept. men packed up my kit and I took another with me home to pack up. Imagine getting an outfit together in three hours to go on a seven thousand mile journey, and be gone a year or more. Such is the life of a fossil man.”
  Brown embarked on the month-long sail to Punta Arenas, during which he was so taken with sea sickness that he was “…first hoping I would die, then afraid I wouldn’t”. He managed to survive the journey, and collected fossils for the next year and a half. Months would pass without word and at times the only evidence of Brown’s continued survival would be the shipment of tons of fossils back to the museum. Mr. Bones would face blizzards, evade quicksand, and even survive being shipwrecked near Tierra del Fuego before heading home. 
  Brown’s greatest discovery came in 1902. Brown and his team had been sent to the badlands of Montana to search through the Cretaceous rock beds of Hell Creek for Triceratops fossils, in particular an intact skull. This rugged terrain was explored by Louis and Clark and is known as the Missouri Breaks today. After supplying themselves at Miles City, Montana, they traveled by wagon for five days to Hell Creek where they made camp at the base of Mount Sheba. Before dinner on the first night, Brown found bone fragments that had fallen down the hill into the creek. After tracing them up the hillside to their point of origin, they started digging, first with plows and scrapers to remove the overlying sediment, then with dynamite when the sandstone became too hard. It would take two years to excavate, and in the end they left a hole that was nine meters long, nine meters wide and six meters deep. The surrounding rock was so hard that they removed everything in large stone blocks which were transported, first by wagon, then by train, back to the museum. The pelvis was massive—it’s block weighed over two tons and was too big to put on a wagon. Brown had to build a sled and drag it with a team of horses the 200 km back to Miles City. It turns out he had discovered the type specimen of Tyrannosaurus rex. A few years later, Brown would return to Hell Creek and discover another, even more perfectly preserved Tyrannosaurus rex which would allow the museum to fully characterize the dinosaur that has captured the imagination of so many in the hundred plus years since its discovery. This “favorite child” of Mr. Bones is still on display in the Museum’s Fossil Hall and speaks volumes about the incredible power of Tyrannosaurus rex, one of the largest carnivores to ever walk the planet.

Monday, June 13, 2011

Why Ice is Slippery

Ice has a hexagonal crystal structure, but what happens
at the surface boundary to make ice slippery?

Ice is a very common solid here on Earth yet one of the most puzzling. Take the seemingly simple question, “Why is ice slippery?”, for example. Common wisdom says that when you step on an icy surface the pressure melts the ice a little bit to create a thin layer of water that acts as a lubricant. It’s due to the unique property of water: the solid form is less dense than the liquid form. We take it for granted that an ice cube will float in a glass of water, but for most material the solid form would sink to the bottom. And because ice has a lower density it is also true that the melting point of ice is depressed as pressure increases. 
The theory goes that as you walk on ice the increase in pressure lowers the melting point of the top layer of the ice and it melts for a brief moment, then refreezes as you pass by. The problem with this explanation is that the effect is very small and would only reduce the melting point by a few hundredths of a degree at most. Yet ice is still slippery when its temperature is far below the melting point.
One possible explanation is that friction plays a part as well. The act of walking on ice creates friction which heats the ice to create a slippery surface. But the problem with this is that ice is still slippery regardless of whether or not you are moving. If you are standing still there is no friction, yet it’s still slippery.
A better theory is that ice has an intrinsic liquid layer. Water molecules at the surface remain unfrozen because there are no molecules above them to hold them in place. This was first proposed in 1859 by Michael Faraday who noticed that two ice cubes will fuse together if they are pressed against one another. Faraday’s explanation for this is that the liquid layers freeze when they are no longer at the surface. But even this theory is not quite correct. 
In 1996, a team led by Gabor Somorjai, a professor of chemistry at Lawrence Berkeley Laboratory, bombarded the surface of ice with electrons. By observing how they bounced off they were able to make an amazing discovery: What actually makes the surface of ice slippery are rapidly vibrating water molecules. These “liquid-like” water molecules do not move from side to side—only up and down. This is an important distinction. If the atoms moved from side to side, the layer would actually become liquid, which is what happens when the temperature rises above 0° C. It turns out that it is this “liquid-like” layer that makes ice slippery.

Monday, June 6, 2011

The Geology of Arches National Park

Landscape Arch, the longest arch in the park and the 
second-longest arch in the world.

Arches National Park contains more than 2,000 natural stone arches—the greatest concentration in the world. But this pales in comparison to the grandeur of the landscape—contrasting colors, textures and landforms unlike anything else on the planet. 
   Located above the Colorado River in southern Utah’s high desert, the park is part of an extended area of canyon country, sculpted by millions of years of weathering and erosion. 300 million years ago, inland seas covered the region. The seas filled and evaporated—29 times in all—leaving behind salt beds up to about 4,000 m thick in places which is known as the “Paradox Formation” today. Later, sand and material carried down by streams from the surrounding uplands buried the salt beds beneath thick layers which later became cemented into rock. Most of the formations at Arches are made of this red Entrada sandstone and tan Navajo sandstone that was deposited 150 million years ago.
Delicate Arch, the most famous of the over 
2,000 arches in the park.
   The salt beds, under tremendous pressure from the weight of the overlying sandstone, became unstable and began to flow. This movement caused the overlying rock to move and buckle. Some sections were thrusted upward into domes, while other sections dropped into the surrounding cavities. Vertical cracks developed which would later contribute to the creation of arches. 
   As the movement of salt deep underground shaped the surface, erosion carried away the younger layers of rock. Water seeped into the rock through cracks and washed away loose material and eroded weaker portions of the sandstone, leaving a series of free-standing vertical fins. Ice formed during colder periods would expand and put pressure on the rock, breaking off chunks and created openings. Many of the fins collapsed, but some that were harder and more resistant to the erosion survived to become the spectacular stone sculptures that we see today. 
   Although the park has timeless beauty, it is not indestructible. The same powerful forces that nature harnessed to carve these extraordinary arches will eventually tear it down. Wall Arch, a photographer’s favorite that was ranked 12th in size, collapsed in August 2008. Landscape Arch, which at 88 m is the longest arch in the park and the second-longest in the world, is facing a grim future at the destructive hands of gravity and erosion. Since 1991, three slabs of sandstone have fallen from the thinnest portion of the arch and the park has had to close the trail which passes beneath it to protect visitors from its eventual demise.

Thursday, June 2, 2011

Alkali Metals in Water

Alkali metal are the Group 1 metals on the periodic table and include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr). All of the alkali metals are naturally occurring, but francium is exceedingly rare. These metals share similar chemical properties and are all highly reactive.