As my devoted readers no doubt realize by now, I’m on a bit of a Rachel Carson kick. I wrote a blog post and produced a radio show about her last fall, and I’m working on an article about her for Johns Hopkins magazine (Carson got her master’s degree at Hopkins). Why this slight Carson obsession? It started with the 50th anniversary of Silent Spring, which got me wondering, as a science writer, how someone armed only with scientific knowledge and words could have such influence. I believe we science writers sometimes sell ourselves short in terms of what we can accomplish, especially in this age of disposable Web writing. Carson can remind us of the potential of writing for impact, not just for mouse clicks.
In 1953, Rachel Carson spoke at a symposium at the American Association for the Advancement of Science’s annual meeting. The topic was the sea frontier. Unlike the other eight panel members with whom she shared a stage, Carson was not a research scientist; she had until recently worked as a staff writer for the US Fish and Wildlife Service. (She was also the only woman on the panel).
At the conference she talked about the book she was writing, The Edge of the Sea, which would be based mainly on her observations, and less on the work of other scientists, as her previous books had been. Carson had scientific training, but it was her writing that earned her the speaking slot: her 1951 book The Sea Around Us had made her the nation’s most famous writer about the oceans and perhaps about all of science.
Although Rachel Carson spent almost her entire career writing about the sea, she is remembered today for her one book about things that happen on land. That book, Silent Spring, awoke the American public to the dangers of many common pesticides, and launched the environmental movement. But while the birth of environmentalism would not have happened exactly when it did and how it did without Carson’s advocacy, it would have happened: Americans would not have tolerated smoggy cities, burning rivers, and toxic chemical clouds for much longer. “I suspect that the audience [of Silent Spring] was close to an environmental awakening,” said Jane Lubchenco, a marine biologist and past head of the US National Oceanic and Atmospheric Administration, at a symposium dedicated to Carson at this year’s AAAS meeting. “No doubt [Carson] catalyzed it, but the ground was fertile.”
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.
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.
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.
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 »
Sebastian Seung could have hired an army of undergraduates to do crucial legwork in his neuroscience lab at MIT. Even with the help of powerful computers that would have taken years. Instead, he and his lab turned it into a game, called it Eyewire, and 10,000 people played it on the first day. Many are still at it. These players hold all conceivable occupations, but in their free time they are neuroscientists: a prime example of scientists partnering with the public in citizen science projects. Collecting or organizing vast amounts of data might take one or two scientists years, but with thousands of people helping, data sets are complete in months or weeks, and discovery accelerates.
The goal of Eyewire is to trace individual neurons in the the tangles of a mouse’s retina. Many people map the same neuron, and results are averaged for better accuracy. Accuracy against the average wins points, though sometimes a player has to be the trailblazer, the first one to map a new neuron, slowly expanding the map. Collectively, the players turn tangles into data, mapping neuron types, connections, and extensions. Seung is hoping to map the retina as a stepping stone to mapping the whole brain, developing a set of connections he thinks may be unique to each person. This connectome, he says, may make each of us who we are. But to map this vast connectome, the pathways of billions neurons in each person’s head, Seung needed help from both a powerful artificial intelligence, the computer game, and thousands of citizen scientists around the world playing it.
If you’re a writer looking for a good symbol, consider the tree. The author of Genesis did, twice: he placed the tree of life and the tree of knowledge front and center in the Garden of Eden. Homer did, too: When his hero Odysseus returned home after twenty years of war and travel, needing to prove his identity to his skeptical wife, Penelope, he used a tree. “Move our bed into the hallway,” Penelope told her servant, laying a trap. (I’m paraphrasing here.) “It can’t be done,” Odysseus protested. “I carved a post of that bed from a living olive tree.” Only then did Penelope believe the strange man was really her husband, as steady as that post.
Trees have long impressed us with their steadfastness; in fact, some trees from Biblical times are still with us today. But a new story I read recently casts trees in a different role. I first came across a version of this story in a paper published in the journal BioScience in 2007. The authors looked at where trees live using a tool known as a “climate envelope,” which is a line drawn on a map around the entire range where a given species is able to survive. The scientists compared climate envelopes for 130 trees under 2007 conditions to those predicted for the end of the century, using the same computer models that the UN’s Intergovernmental Panel on Climate Change bases its forecasts on. On average, they found that trees’ envelopes moved 700 kilometers north, nearly the distance from Memphis to Chicago.
So does that mean our trees will be moving north as things get warmer? Traveling trees can make great stories: Shakespeare’s Macbeth was vanquished when Birnam Wood moved a few miles to his fortress at Dunsinane Hill. And it would be dramatic indeed if future northern woodsmen and women hunt deer among sprawling live oaks and big-leaf magnolias instead of spruce and pine trees. But the scientists who wrote the BioScience paper noted that actual trees are unlikely to track their climate envelopes’ northward migration in the coming years, at least if unassisted by humans. Trees can “move” up to a few miles in a generation, by setting their seeds aloft in the wind or encasing them in a shell so they can survive a trip in the gut of an animal. But tree generations are long, and most seeds land close to home. Sugar maples, for example, lead a chaste adolescence, and don’t start making seeds until the age of 22 or so. They then send out seeds attached to little helicopters, which spin and float at most the length of a football field before touching down. Scientists estimate trees’ maximum migration rate to be around 50 kilometers per century, with many traveling far slower—a tortoise’s pace in this race.
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.
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 »