There is no life without phosphorus. It helps cells transport energy by being a part of the biological molecule. The center of the molten planet was where any phosphorus that was present would have been sequestered.
Where did it come from?
It might have been from the stars.
The materials that coalesced into the planet were made of phosphorus. The Earth's core is where most of the initial element is gathered. It likes to be in iron. The planet's core was formed by so much of Earth's iron that it took much of the phosphorus with it.
When Earth formed, there was no phosphorus available for life. It took a long time to arrive on Earth. Scientists had thought that meteorites and comets might be the source. A new study suggests that there might be something in the dust.
The study titled "Phosphorus Chemistry in the Earth's Upper Atmosphere" was published in the Journal of Geophysical Research Space Physics. John Plane is the lead author.
Thousands of tons of dust reach the Earth each year. The smallest particles of dust are a few hundred micrometres. It's mostly silicate minerals, the most common type of minerals on Earth. Carbonaceous material, sulphides, metals, and other minerals and compounds are included in some cosmic dust. asteroids and comets can produce it through a variety of processes.
The skies over La Silla observatory are lit by moon and zodiacal light. Zodiacal light is thought to be reflected from the dust in the plane of the zodiac. Alan Fitzsimmons is an ESO.
Before it is useful in living things, it must be in the form of metal phosphites. The authors show in the paper that dust can go through a series of chemical reactions as it travels through the atmosphere, eventually stabilizing and settling to the Earth's surface.
Cosmic dust, or interplanetary dust grains, heat up when they hit Earth. The heat causes them to melt. The release of molecule containing phosphorus was detected in previous laboratory studies. Modelling showed that IDPs could be a significant source of phosphorus over time.
The authors wanted to better understand the dust and how it could be delivered to Earth. The lab results from previous experiments were combined with theoretical predictions for other chemical reactions that haven't been studied in the laboratory to do that. They incorporated the model into a global climate model.
The figure shows how dust can create important forms of phosphorus. The process takes place in the lower thermoosphere. There are two compounds at the bottom. The green arrows show the important pathway from OPO to H3PO3. The red arrows show the pathway from OPO to H3PO4. Plane et al 2021.
The results supported the idea that dust from the stars is the main source of Earth's biologically useful phosphorus. The Southern Andes, the Northern Rockies, and the Himalayas were shown in the global climate model how much phosphorus they might receive. The team found that the Earth might be encircled by a narrow atmospheric layer of a molecule called OPO at an altitude of about 90 km.
The figure shows the deposition of the mineral over the Earth. The larger amounts can be seen over the northern Rocky Mountains, the southern Andes, and the Himalayas. Plane et al 2021.
Some of the phosphorus that enters Earth's atmosphere is biologically useful. The researchers estimate that about 10% of metal phosphites form and settle to the Earth's surface.
The authors point out the utility of their study. Two important conclusions can be drawn from their paper.
The source of P from IDPs is provided by the oxidation of P in the form of sub-micron-sized smoke particles. The bioavailable phosphites are more likely to be the fraction of the phosphorus.
If they are correct, their results will have a big impact on our understanding of the history of life on Earth. The Earth's core was unable to hold initial phosphorus for life. Their model shows how dust can be a continuous source of phosphorus.
Future research could explain this in more detail. Future research might be able to find out if there was a change in the amount of phosphorus from the dust before and after the GOE.
It is just one more example of how many things had to happen for life to do what it has done.
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