An assessment of the amount and types of organic matter contributed to the Earth by interplanetary dust

A continuous, planet-wide rain of about 30,000 tons/year of interplanetary dust accretes onto the Earth. The mass-frequency distribution of this dust is sharply peaked at about 400 μm, but the larger particles are most severely heated during atmospheric deceleration, with many of them vaporizing as meteors. Modeling of the peak temperature distribution experienced during atmospheric entry indicates that particles near 10 μm in size contribute the bulk of the mass that is not heated above 600 °C, which is believed to be the mean pyrolysis temperature of extraterrestrial organic matter. We have used infrared spectroscopy and X-ray absorption near-edge structure spectroscopy to characterize the types and abundance of organic matter in ∼10 μm interplanetary dust particles collected from the Earth's stratosphere. These particles contain high abundance, from a few to over 90 vol%, of carbon, including percent-levels of both carbonyl (C≡O) and aliphatic hydrocarbons (C-H ₃ and C-H ₂ ). We estimate that, in the current era interplanetary dust contributes ∼15 tons/year of unpyrolized organic matter to the surface of the Earth. During the first 0.6 billion years of Earth's history, this contribution is likely to have been much greater.