Intentionally? Meteors deliver iron for habitability

Photo credit: NASA/Bill Dunford.

Could life exist without meteors? Don’t imagine those rare blockbusters that leave huge craters and kill everything hundreds of miles away. Instead, imagine harmless shooting stars that delight astronomers, like the Geminids that adorn the December sky. The brightest of them are about the size of a pea. Better yet, think of meteors so small you can’t even see their trails. These hidden particles provide essential iron to the planet, according to a new NASA study.

What we cannot see with the naked eye is the regular shower of much smaller meteoroids, often called cosmic dust, this bombards our atmosphere every day of the year. Produced during collisions of asteroids or comets vaporized by the Sun, some of this material burns up when it enters the atmosphere, much like the Geminids but on a much smaller scale. About 55 miles above Earth, the tiny fireballs leave a puff of even tinier particles, called meteoric smoke. The particles stick together and grow like tiny snowballs as they fall to Earth over several years. [Emphasis added.]

NASA’s Solar Occultation Experiment for Ice (SOFIE), launched aboard an orbiting satellite, began collecting data on this meteor smoke in 2007. It wasn’t until recently, however, that scientists have been able to determine what the smoke particles are made of and how much they are. mass lands on the planet.

The particles are extremely difficult to study, being one thousandth the width of a human hair. SOFIE watches the sun through the atmosphere at every sunrise and sunset, gaining spectral information about gases and solid materials obscuring sunlight. From the spectra and angles of incidence, the scientists were able to determine the ratios of elements in the particles, specifically iron, magnesium and silicon.

The results of the analysis allowed for nine possible mineral candidates that make up meteoric smoke. NASA says another team from the University of Leeds had independently recovered samples of cosmic dust from the ice of Antarctica. Its elemental ratios matched one of nine candidates on the SOFIE list: the iron-rich mineral olivine. Their estimates of the amount of material deposited on earth also matched the results of the SOFIE team. The answer is 25 tons per day!

Special delivery

Olivine is abundant on earth, providing essential iron for photosynthesis in land plants. However, most of the planet’s photosynthesis takes place in the ocean. How do these photosynthetic microbes, such as diatoms, get their minimum daily iron requirement? NASA hints that it could be a special delivery from the outer reaches of the solar system.

There is also speculation among scientists about other effects. 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 away as dirt dust before quickly sinking. Some scientists suggest that another source could be meteor smoke that drifted from the mesosphere. It is therefore possible – but not certain – that there is extraterrestrial iron contributing to photosynthesis in the ocean!

As amazing as this possibility is, it makes sense from a design perspective. Meteoric smoke drifts gently over the years, unlike terrestrial dust which sinks quickly when blown over the sea by the wind or carried away by rivers. And since meteoric iron arrives from all directions, it can nourish photosynthetic organisms all over the world, where 70% of the planet’s surface is water. The startling finding raises the question of whether the earth’s rich biosphere could thrive without this delivery system from space. Is meteor smoke another requirement for a habitable planet?

The observation is reminiscent of our article on the varnish of the desert. Readers may recall the new discovery that explained the origin of this manganese-rich mineral that darkens cliff faces in deserts. In this story, microbes living in dust were found to carry DNA to bare walls via winds, creating additional habitats that would otherwise be too hostile to life.

SOPHIE’s findings on meteor smoke help explain another long-standing mystery: the origin of noctilescent clouds (see time-lapse videos of these in the article). Found in polar latitudes at night, these “night” (noctilucent) clouds have been observed by many people on rare occasions with the right angle of sunlight and clear skies. Atmospheric scientists had estimated the height of clouds in the mesosphere and in 2001 determined that they were composed of ice. They were puzzled, however, how the ice could form so high. Atmospheric ice needs dust as a core on which to crystallize, but it was thought there was little dust at 55 miles altitude. Meteor smoke particles provide the answer: they could be the cores of ice grains, as NASA also reported. Spectators of noctilucent clouds could watch the iron delivery trains in action!

diatom communication

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 suggestive identifying term “infochemistry”):

Scientists assumed diatoms, which are single-celled phytoplankton, could only report and communicate with each other 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 at the correct frequencies, diatoms in a laboratory synchronized their behavior, lining up vertically in the water and wobbling in time with each other, suggesting that they are capable of coordinated social behavior.

The Dance of the Diatoms: Imagine tiny microbes partying under glowing lights. It’s cool. Physicist Idan Tuval tells Robitzki how he got involved in research and why it fascinates him.

There was information in the literature about diatoms having encoded in the genome the genes of certain photoreceptors in the red and infrared band. There was no clear indication of why they would have this. We’re talking about organisms that live mostly in the water column—they live in a very blue environment; no red light around…. We just thought maybe — we wanted to test these hypotheses, of course — they can actually feel.

Using creative techniques, the Tuval team observed the orientation of diatoms in the water column and discovered that “they wobble, oscillate as they sink.” To test if the red light from photosynthesis was acting as a coordination signal, Tuval sent them this wavelength. They lined up as expected. The purpose of this coordinated dance is not yet clear, but the presence of red photoreceptor genes suggests a communal function.

We are simply talking about the natural autofluorescence of chlorophyll, which is there for most photosynthetic microorganisms. So if there’s a photo answer that links behavior to light emission based on this very simple mechanism, that’s a huge change in the field. He tells you that there is a clear phenomenon – which has not been taken into account at all – that allows cells to feel and react. And that changes things.

Maybe the light helps them find each other for sexual reproduction; Tuval is studying this and looking to see if it is a widespread phenomenon in other species. As often happens, a surprise creates research opportunities for further discoveries.

It was refreshing to see fascinating research with design implications and no mention of Darwinian evolution. Tuval had “drifted” into the theory of evolution earlier in his career, he says: “I slowly drifted into the behavior of microorganisms and how physical stresses are involved in behavior and development and evolution of life forms.” In this game-changing work now, he apparently didn’t need that assumption.

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