The Evolution of Air

I recently read The Invention of Air by Steven Johnson. It is about Joseph Priestley and the Enlightenment movement that he was part of in England and America.

Joseph Priestley is the man who is commonly credited with discovering oxygen. Unfortunately Priestley was neither the first to isolate oxygen (that was Carl Scheele), the first to understand its true nature (Antoine Lavoisier), nor the one to give it the name we use today (Lavoisier again). Priestley was the first to publish the fact that he had isolated oxygen, and he was already well known for other pursuits, so his is the name we usually associate with oxygen.

But what I really want to know is - what the heck does the title of the book mean?

Obviously, no one including our hero Priestley "invented" air. The title must be a metaphor. I went to engineering school, so I won't be much help with the metaphors.

According to one of the reviewers quoted at the front of the book, who was clearly a literature major, the "invention of air" refers to "how groups of scientists, natural philosophers, religious leaders, and politicians served as cultural petri dishes in which ideas were discussed, experimented with, discarded, or accepted".

This is definitely one of the themes of the book. But using the K.I.S.S. principle of metaphor interpretation, I noticed that the few times the author actually used the word "invent" in the book, he was referring to evolution - as in 'Mother Nature invented this', or 'plants invented that'.

Supporting my simplistic decoding of the title is the fact that the author stresses the one thing Priestley unequivocally did discover - that whatever it was plants breathed out, animals breathed in. Priestley was the father of ecosystem science. For this he received the Copley Medal, the Nobel Prize of his day. The presenter of this award in 1773 could have been making a presentation today on "ecosystem services":

From these discoveries we are assured, that no vegetable grows in vain, but that from the oak of the forest to the grass of the field, every individual plant is serviceable to mankind.

So where does evolution come in? The author explains that when our Earth came into being, its atmosphere did not contain any oxygen. Some of the earliest life forms, cyanobacteria, evolved to use what they had available to them - water, sunlight and carbon dioxide. Their waste product, oxygen, was deadly to the other (anaerobic) microorganisms they were battling for world dominance. Great plan!

It would be millions of years before plants evolved that could make use of some of this waste oxygen, along with the water, sunlight and carbon dioxide, and produce even more waste oxygen. (Yes, plants do use oxygen for respiration. But since they produce more oxygen through photosynthesis than they use for respiration, we don't think of them as using oxygen too.)

It would be millions more years before animals evolved that would finally use up some of this waste oxygen. Before atmospheric oxygen levels settled into equilibrium at today's 21%, they climbed as high as 35%. This created some huge plants and animals in the Carboniferous period - mosses 130 feet tall, dragonflies with a wingspan of 2 1/2 feet, and millipedes 8 feet long.

Here's the 8 foot millipede (Arthropleura), advertising BBC's show Walking With Monsters. I'm sure glad I missed the Carboniferous.

Eight Ways Elephant Seals Have Evolved

I took these photos of elephant seals at Piedras Blancas State Marine Reserve in California. Here are some interesting ways that elephant seals have adapted to their harsh environment:

1. As you can guess, their name comes from the large noses of the males. Besides being a way to scare off competing males and attract the ladies, these noses may also help males conserve moisture when they are out of the water. Elephant seals can spend up to 3 months at a time “hauled out” on the beach during breeding season, with their stored blubber their only source of energy and moisture. It is believed that some of the moisture they exhale is captured and reabsorbed by their nose.


2. Another way elephant seals conserve moisture is by producing urine that is more concentrated than many other animals. Yuck, enough said.


3. Elephant seals and monk seals are the only mammals that molt their skin all at once, rather than shedding it continuously in small amounts. This allows them to shut down blood circulation near their skin when they are in the water, helping them to keep warm, conserve energy, and build up that all-important blubber. I was at Piedras Blancas in late July, which is molting season for the males. The tan seal in the photo below has some good molting going on.



4. Elephant seals have really bad sleep apnea. But in their case it is a good thing, allowing them to conserve energy while on the beach without food or water. They can go without breathing for up to 30 minutes while lounging on the beach.


5. Another way that female elephant seals conserve energy is through “delayed implantation” of their embryos. The breeding season includes giving birth, nursing pups, and being impregnated again before going back into the water. But the new embryo will float around in the uterus for 3 or 4 months before attaching to the uterine wall, giving mom a chance to eat and build up her strength before sharing with junior.


6. Elephant seals can dive as deep as 5000 feet. The only mammals that can dive deeper are sperm whales and bottlenose whales. One way they accomplish this is by completely collapsing their lungs before diving, driving out all the air. This prevents nitrogen in the air from dissolving in their blood under high pressure, and coming out when they resurface causing the “bends”.


7. Elephant seals can stay under water for over an hour, then resurface for only a few minutes before diving again. They are able to do this by storing a higher concentration of oxygen in their blood and muscle tissue than other mammals.


8. Elephant seals have been observed eating stones before hauling out of the water for the breeding and molting seasons. When they return to the water, these stones come out the other end. It is believed this helps them fill their stomach while fasting.

Patience Pays Off for Pothole Populations

The photo above may not look like much, but it took hundreds of years to create. It is a pothole in the bedrock of Mather Gorge, which I saw on my recent trip to the Great Falls of the Potomac.

The red lines I drew show the general shape of the "pothole". The blue chicken scratch was my attempt to show water swirling inside, carving out the pothole. About 35,000 years ago, during the Wisconsin Glaciation, huge amounts of melt water from the glaciers poured through the Mather Gorge. The spot where I was standing to take this picture was under water.

A turbulent vortex of water, created by some obstacle such as a rock, started spinning above the future location of this pothole. The swiftly flowing water carried sand and stones, which acted like sandpaper against the bedrock. Over hundreds of years, a circular pothole was formed.

In the thousands of years since, weather and water have caused the large crack at the back of the pothole, and completely ripped off the front half. What you see is half a pothole.

The above photo is the largest pothole I came across. It was about 5 or 6 feet deep. There are many potholes along both banks and on the islands in the river. Here is a top view of a small one, only about a foot across. It became filled with silt over the years.


Where the rock is softer, it gets eroded much quicker, and can form very large potholes. The pothole below is in Moab, Utah. The photo is from the Utah Geological Survey.

As you can see, if the pothole has not cracked or been filled with silt like the ones I saw, it will hold water. This pothole in Utah is in a dry area, and the water at the bottom is rain.

Amazingly, organisms have adapted to live in these transient pools of rainwater. They include mites, nematodes, tardigrades, and many others. The conditions in the pools are harsh, with wide temperature variations including freezing of the water during the winter. Oxygen and pH levels also swing widely. The smaller pools periodically dry up completely.

Some residents of these potholes, or at least their eggs, have been known to live dormant for many years without water. Some of these organisms are so well adapted to their harsh environments that they have not changed in millions of years. Their ability to withstand these conditions makes them of great interest to scientists looking for life on other planets. Click here to read more about this in NASA's Astrobiology Magazine.

Darwin Contemplates the Caterpillar - Arsenura Armida

The photo above is from a family vacation to Mexico. It has taken me four years, but I have finally identified the creatures on the tree. The tour guide just called them "giant caterpillars", but they were much bigger than any caterpillar I had ever seen.

Thanks to the wonderful website WhatsThatBug.com, I found out that four other people had seen the same caterpillars, one in Honduras and three in the same area we visited near Cancun (the tour guides must bring everyone past the same tree!). They are Arsenura Armida, a type of silk moth from the family Saturniidae. Other than being unusually large and producing low quality wild silk, these caterpillars stand out due to their bright coloring.

My photo shows these caterpillars in their final "instar", or final molting phase, before they transform into pupae. Here is a website that shows some of the other instars, along with a lot of other technical details. You can see that the caterpillars are even more brightly colored in their earlier instars. If you compare the photos from the first instar to the last you would hardly say they were the same species. (You can tell my photo is the final instar because their "horns" have fallen off.)

An interesting historical note is that the great Charles Darwin was stumped by the colorful displays of caterpillars like these. Darwin's explanation for bright colors was that they aided in sexual selection (think of bright red male cardinals competing for the attention of brown females). But brightly colored caterpillars did not fit Darwin's theory, since caterpillars do not mate.

Darwin turned to his colleague Alfred Russel Wallace for help in answering this question. Wallace had published a paper on natural selection before Darwin did. Wallace made many of the same observations on his visits to the Malay Archipelago that Darwin made in the Galapagos Islands. Some science historians have suggested that Darwin "borrowed" ideas from Wallace for his On the Origin of Species, and that Wallace should have received some of the fame that went to Darwin.

It was Wallace, with the help of experiments completed by John Jenner Weir, who proposed that the caterpillars that had evolved bright colors were the same ones that had evolved a bad taste to birds. The bright color was a warning to their predators, helping them remember which caterpillars tasted bad. Fitting in perfectly with this theory was the fact that caterpillar species that evolved camouflage coloring were the ones that tasted good to the birds (when they could find them!).

This concept of warning coloration developed by Darwin's associates is known as aposematism.

Arachnid Lungs Evolved From Horseshoe Crabs

I have been watching videos of the BBC television series Life in the Undergrowth with David Attenborough. It starts off by explaining how life got in the undergrowth to begin with, in other words, how it crawled out of the sea. One example he discusses is the horseshoe crab.

The horseshoe crab is actually not even a crab, it is an arthropod of the subphylum chelicerata, which means it is more closely related to the arachnids like spiders, scorpions and ticks than it is to crabs. Sir Attenborough showed thousands of horseshoe crabs crawling out of the water for their annual spawning. Living in prime horseshoe crab territory in New Jersey, I have seen many of these ancient creatures gracing our beaches.

Attenborough explained that since horseshoe crabs were among the first animals to develop the ability to venture onto land, they had a distinct advantage in that they could keep their eggs away from their enemies who were still in the water. They no longer have this advantage, since many birds look forward to the annual horseshoe crab spawn every year. This is especially true of the red knot, which feasts on the horseshoe crab eggs during its migration stop-over in the Delaware Bay. This species of sandpiper makes an amazing annual migration from one end of the Americas to the other, from the Canadian Arctic to Tierra del Fuego at the southern tip of South America!

The adaptation that allowed the horseshoe crab to venture onto land was the "book gill", which you can see in the top photo just above his tail. Each of the folds that is visible in the photo has many more folds within it, with the overall structure looking like the pages of a book. This gill is on the outside of the horseshoe crab's body, so as long as he keeps it moist with the small amount of water in the wet sand, he can live out of the water up to a week. The many folds increase the surface area for gas exchange to his blood.

Fast forward to modern-day spiders, close relatives of the horseshoe crab. Below is a cross-section diagram, with #16 being the "book lung". This is essentially the book gill of the horseshoe crab, evolved to be located within the spider's body, and supplied with air through a small opening. Scorpions have a similar setup. Pretty amazing that these small land animals have lungs evolved from an ancient sea creature. Thanks to Wikimedia Commons for the photo and diagram.