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Posts Tagged ‘science

A River Runs Through It

 

 

What you see here is over 300 million years of geological history at Goosenecks State Park in Utah. You’ve seen similar vistas before, such as looking into the Grand Canyon, and there’s a reason for that.

At the bottom of these chasms is the San Juan river, and at a glance you might imagine the river slowly carving its way down through rock over eons. It didn’t happen that way. What actually happened is much more interesting.

You’ve seen photos of rivers that meander back and forth in a form called oxbow tails, such as this one in the Innoko National Wildlife Refuge in Alaska:

 

These develop in areas that have low gradients, i.e., the upriver areas are very slightly higher than downriver, just enough for the water to slowly flow downward. The San Juan developed in that way, over 300 million years ago.

But rivers like these don’t cut into rock. They actually tend to collect and carry sediments, then drop them at turns, which is why it ends up winding back and forth.

The continental crust underlying the San Juan river broke off from the supercontinent Pangea and wandered around the globe. It’s still moving west, at about the speed fingernails grow; if you’re living in North America, you’re along for the ride right now.

And so through eons, about 280 million years, the river placidly plodded along, providing dinosaurs and other animals with drinking and bathing water.

Then the mountain building began, in fits and starts, over millions of years. Today that process is called the Laramide and Sevier orogenies. A thin dense layer of underwater basalt rock that makes up the Pacific plate began diving under North America. The angle of the collision was very shallow, but still powerful enough to squeeze and deform the rocks that make up the continental crust.

That compression created the column of mountains that stretch from Canada down through the US and into Mexico. The average thickness of continental crust runs between 22-25 miles. Imagine, if you can, the epic scale at work here; much of the western basin, an area that was once the bottom of a shallow inland sea, being slowly pried upwards. You can duplicate the pattern on a smaller scale by pushing a piece of tablecloth.

The new mountains transformed the gradient of the surface water’s flow. Upriver was now significantly higher than downriver, which in turn generates faster water flow.

Normally when water runs fast, it flows relatively straight, creating long classic valleys. But this river was already formed. The new, faster flow was strong enough to carry sediments out and further downhill, but not strong enough to alter the shape of the river. So it carved down through the rock…in 20 million years.

So what you see here, in a sense, is a region that has been power washed by an incessant high-flow river running 24/7 for 20 million years, steadily working its way down through 300 million years of layers. This all happened in the last 15% of the river’s existence.

So it doesn’t take 300 million years to carve this deep channel. Twenty million years and fast water is enough to make it happen.

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Written by Influential Prose

May 10, 2015 at 10:58 am

What’s the Oldest Form of Life?

When I was in high school, we’d study simple forms of life – single cell life,  like a paramecium. And the thing that consistently impressed me was how incredibly complicated these forms of life were. We’d examine a single, basic cell, and find it was amazingly sophisticated. It was enough to make one think that maybe, just maybe, the intelligent design people were on to something.

For much of my life, I’ve been mildly interested in building up a sense of the sequence of life. Wouldn’t it be cool to look at forms of life around us and know, roughly, how long it’s been around?

The puzzle of complexity and the mystery of age drove much of my interest in biology for years. And the key to understanding both is the timeline of development.

We know the earth was frequently subject to heavy-duty bombardment by meteorites during the first half-billion years. This pounding was fierce enough that it’s entirely possible that simple forms of life arose and were wiped out several times.

We also know that the earliest evidence of life we can find dates back the time when the bombardment was winding down. Those early life forms were single cells. And that’s how matters remained…

…for the next 2.5 billion years.

Two and a Half . Billion. Years.

Evolution is driven by changes in the environment. Life that can adapt to change survives. Life that can’t…dies. Sometimes it’s the weird mutant cell that survives, say, a period where it’s colder than normal. That mutant proliferates while others fade away. The mutant moves into colder environments while it’s cousins remain in the tropics. Single cells adapted to a variety of environments, including competition with their own expanding numbers. The development of single-cell life, including the arms race of single-cell biological warfare, went on for time out of mind.

No damn wonder they’re so sophisticated. This chart of cellular biochemical and metabolic pathways resembles a large city map:

biochemicalpathways

All the oldest forms of life began in the ocean. It was only about 500 million years ago – half a billion years – that life moved onto land. There are living fossils among us. Sponges date back 635 million years. Horseshoe crabs, 435 million years. Sharks, over 350 million years. Alligators, more than 200 million years. Ginko trees – there are many of them in Washington, DC – haven’t changed in 170 million years.

But to find the oldest form of life, you need look no farther than the cells of your own body. We are, all of us, walking cell colonies. The cells that form us are, of course, far more advanced than the earliest cells, and they got that way because they had 2.5 billion years to find their groove.

The most ancient forms of life are the building blocks of your life.

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Written by Influential Prose

November 18, 2009 at 8:59 pm

The Biology of Deafness

Employment Matters column, i711.com


According to the biology departments at Gallaudet University and the Medical College of Virgina, at least 85% of deaf people will marry another deaf person.

Many of those marriages will eventually include children, and if their parents became deaf by genetic causes, there’s certainly a chance of the children being deaf too. Among the general population, about 1 in 1,000 children in the US is born profoundly deaf.

About half of all deaf people are genetically deaf, and the other half became deaf through environmental causes. Environmental causes include premature birth, viruses that reach the fetus, and certain drugs that can affect the fetus.

Genes come with on/off switches, so not all genes are working all the time. Some genes are only read during fetal development, others during puberty, and others can be on or off depending on the activity of other genes or the environment.

The genes that cause deafness can be either dominant or recessive. If a gene is dominant, it will be active when only one copy of the gene is present. Recessive genes are only active when two copies are present.

Everyone gets genes from both parents. Dominant genes for deafness can come from either parent, but a recessive gene for deafness means both parents must pass it on for that gene to be active.

Most genetically deaf people inherit recessive genes, which is why deafness can sometimes skip generations – childen may get only one recessive gene from their parents, and so become carriers of the deafness gene, but they won’t be deaf themselves.

Working out how genes interact with each other and the environment is an extremely complex subject, and there are at least several hundred genetic changes that can lead to deafness. But just a few common causes dominate the list. You probably know of some of them, either from personal experience or through people you know.

Genetic causes for deafness are grouped in two ways. One group is linked with other traits, or syndromes. In the second group, deafness appears unrelated to anything else.

The first, syndromic group, include Usher’s, Waardenburg and Pendred syndrome. One feature of Waardenburg is a forelock of white hair, so if you’ve seen that, you’ve seen an example of syndromic deafness. These forms of deafness arise when mutations in a gene or a group of genes affect more than just hearing.

Genes provide instructions – you can think of it as a recipe – for making proteins. Our bodies use some proteins for more than one purpose. If a mutation affects one of these multi-purpose proteins, the effect shows up as a syndrome. Different areas of the body feel the impact of the missing or incomplete protein.

There are also at least 30 genetic causes of deafness that are not apparent through appearance or other issues. Most deaf people – 70 to 80% – are in this group. Of the major causes in this group is a mutation of the GJB2 gene.

This gene makes a protein called connexin 26, which makes a critical part need by cells to communicate with neighboring cells. This communication trouble at the cellular level scales all the way up to the whole individual!

Many genes in both groups have been mapped – their locations are precisely known, and tests for some are available. Some genes are so large that testing them for deafness-related mutations is too expensive, but among the smaller and well-known deafness genes, it’s possible to arrange tests. There are still some genetic causes of deafness where the location of the gene remains a mystery.

Both genes and our environment have a powerful influence on the people we become. But in the end, how we play the environmental and genetic cards we’re dealt has the greatest impact on our lives. The actions we take and the choices we make define us more than anything else.

Related Links:

Hereditary Hearing Loss Homepage

Deafness and Hereditary Hearing Loss Overview

Chart of Inheritance Percentages

Basic deaf-related Genetics

Nonsyndromic Deafness

Finding Genes for Non-Syndromic Deafness

Deafness-related Gene Testing

Written by Influential Prose

September 30, 2009 at 11:54 pm