Physics, Earth & Space
By Design? Meteors Deliver Iron for Habitability
Could life exist without meteors? Don’t picture those rare blockbusters that leave immense craters and kill everything within hundreds of miles. Instead, picture harmless shooting stars that delight stargazers, like the Geminids that grace December skies. The brightest of those are about the size of peas. Better yet, think of meteors so small you cannot even see their trails. These hidden particles deliver essential iron to the planet, says a new NASA study.
What we can’t see with the naked eye is the steady rain of much smaller meteoroids, often called cosmic dust, that bombards our atmosphere every day of the year. Produced when asteroids collide or comets are vaporized by the Sun, some of this material burns up when it enters the atmosphere, just like the Geminids but on a much smaller scale. About 55 miles above Earth, the miniscule fireballs leave a puff of even tinier particles, called meteoric smoke. The particles stick to each other and grow like tiny snowballs as they fall to Earth over several years. [Emphasis added.]
NASA’s Solar Occultation for Ice Experiment (SOFIE), launched aboard an orbiting satellite, began collecting data on this meteoric smoke in 2007. Only recently, however, have scientists been able to determine what the smoke particles are made of, and how much of their mass lands on the planet.
The particles are extremely difficult to study, being one-thousandth the width of a human hair. SOFIE stares at the sun through the atmosphere each sunrise and sunset, gaining spectral information on gases and on solid material occulting the sunlight. From the spectra and angles of incidence, scientists were able to determine ratios of elements in the particles, particularly iron, magnesium, and silicon.
The results of the analysis permitted nine possible candidate minerals that make up the meteoric smoke. NASA says that another team from the University of Leeds had independently recovered samples of cosmic dust in Antarctic ice. Its elemental ratios matched one of the nine candidates in SOFIE’s list: the iron-rich mineral olivine. Their estimates of the amount of material deposited on the earth also matched the SOFIE team’s results. The answer is 25 tons per day!
Olivine is abundant on the earth, providing essential iron for photosynthesis in land plants. Most of the planet’s photosynthesis, however, takes place in the ocean. How do those photosynthetic microbes, such as diatoms, get their minimum daily requirement of iron? NASA hints that it may come special delivery from the far reaches of the solar system.
There is some speculation among scientists about other effects as well. One of them is the phenomenon of iron fertilization. Iron is essential for photosynthesis, the process by which plants convert sunlight into sugar. In the ocean, where phytoplankton reside, iron can be hard to come by. Much of it blows in as dust from land before sinking quickly. Some scientists suggest that another source might be meteoric smoke that has drifted down from the mesosphere. So it’s possible — but not certain — there’s some extraterrestrial iron contributing to photosynthesis in the ocean!
Astonishing as that possibility is, it makes sense from a design perspective. Meteoric smoke drifts down gently over years, unlike land dust that sinks quickly when blown over the sea by wind or washed in by rivers. And since meteoric iron comes in from all directions, it can feed the photosynthetic organisms all over the globe, where water comprises 70 percent of the planet’s surface. The surprising conclusion raises the question of whether the rich biosphere of the earth could thrive without this delivery system from space. Is meteoric smoke another requirement for a habitable planet?
The finding is reminiscent of our article on desert varnish. Readers may recall the new discovery that explained the origin of that manganese-rich mineral that darkens cliff walls in deserts. In that story, microbes living in dust were found to ferry DNA up to bare walls via winds, creating additional habitats that would otherwise be too hostile for life.
SOPHIE’s findings about meteoric smoke help explain another long-standing mystery: the origin of noctilucent clouds (see time-lapse videos of them in the article). Found at polar latitudes at night, these “night-glowing” (noctilucent) clouds have been observed by many on rare occasions with the right angle of sunlight and a transparent sky. Atmospheric scientists had estimated the clouds’ height in the mesosphere, and by 2001 had determined they were composed of ice. They were puzzled, though, how ice could form so high. Atmospheric ice needs dust as a nucleus on which to crystallize, but little dust was thought to exist 55 miles up. Meteoric smoke particles give the answer: they could be the nuclei for the ice grains, as NASA has also reported. Viewers of noctilucent clouds could be watching the iron delivery trains in action!
Speaking of photosynthetic microbes in the ocean, there’s news about diatoms, the ubiquitous marine microbes that produce a quarter of the oxygen we breathe. Diatoms communicate with light! Dan Robitzki explains in The Scientist (watch for the ID-suggestive term “infochemicals”):
Scientists assumed diatoms, which are single-celled phytoplankton, could only signal and communicate with one another by secreting infochemicals. The new study suggests that the pelagic diatom Pseudo-nitzschia delicatissima can also communicate with others through red and infrared autofluorescence triggered by exposure to sunlight. When exposed to lights of the right frequencies, diatoms in a lab synchronized their behavior, aligning vertically in the water and wobbling in time with one another, suggesting that they’re capable of coordinated social behavior.
The dance of the diatoms: imagine tiny microbes having a party under glowing lights. That is cool. Physicist Idan Tuval tells Robitzki how he got involved in the research and why it fascinates him.
There was some info in the literature about diatoms having encoded in the genome the genes for some photoreceptors in the red and infrared band. There was no clear indication of why they would have that. We’re talking about organisms that live down in the water column most of the time — they live in a very bluish environment; no red light around…. We just thought that maybe — we wanted to test these hypotheses, of course — they can actually sense each other.
Using creative techniques, Tuval’s team observed the orientation of diatoms in the water column and found that “they are wobbling, oscillating around, while they are sinking.” To test whether the red light from photosynthesis was acting as a coordination signal, Tuval shined that wavelength at them. They lined up as predicted. What purpose this coordinated dance serves is not yet clear, but the presence of the genes for red photoreceptors is suggestive of a community function.
We’re talking about just the natural autofluorescence of chlorophyll, which is there for most photosynthetic microorganisms. So if there is a photo response that links behavior to emission of light based on this very simple mechanism, that’s a huge change in the field. It’s telling you that there’s a clear phenomenon — that has not been taken into account at all — that allows cells to sense each other and react. And that’s a game changer.
Perhaps the light helps them find each other for sexual reproduction; Tuval is researching that and looking to see if this is a widespread phenomenon in other species. As often happens, one surprise creates research opportunities for more discoveries.
It has been refreshing to see fascinating research with design implications and no mention of Darwinian evolution. Tuval had “drifted” toward evolutionary theory earlier in his career, he says: “I slowly drifted towards the behavior of microorganisms and how physical constraints are involved in the behavior and the development and evolution of life forms.” In this game-changing work now, he apparently had no need of that hypothesis.