Astrobiology: Organics in the Morning

SandiaThis morning life is starting to emerge from the data. I’m in the amphitheatre Rebecca praised the other day, where I can have good access to electricity and comfortable chairs. Unfortunately, the trade off for comfort and power appears to be really bad sound quality. The first two talks I heard were given by scientists who addressed their PowerPoint slides, heads generally turned away from the mic, and all I heard was a long series of mumbles punctuated with “s”s and “t”s that popped and hissed. The second talk at least had a lot of words on the slides.

This well-worded PowerPoint was on vertical geochemical profiling across a 3.33 billion year microbial mat from Barberton (translation: the looked at the fossil remains of a microbes that had grown in layers, one atop another). This particular fossil discussed is one of the oldest high quality fossils (and in fact the speaker started by saying pointedly into the mic – I think in a ribbing manner – to an early speaker that when he said there are no good fossil microbial mats from early Earth, he was wrong – just plan wrong (she actually used much stronger language, delivered with a British accent, that made everyone laugh).) I wish I could have heard everything she said clearly. Here is what I did grock: There are some really well persevered early microbial fossils that are very similar to modern biolaminared sediments (sediments that are filled with different layers of often different colored microbes) on tidal flats. These microbes form layers that are sometimes only microns thick! In the fossils, we see the same fine layers. The fossils are preserved by fine silicates (the stuff that makes sand and glass). When alive, these microbes “fed” in layers, with microbes on the top using the Sun to grow, and nutrients then passing (via death and excretion) from layer to lower layer.

Finding fossils of such large age indicates that life pretty much popped up as soon as it possibly could have on the early Earth. This raises the question – how? While the origin of life was not discussed, several presenters looked at the origins of organic materials.

In a presentation by Jennifer Blank, the “Modeling of Comet-Earth Collisions to Assess Survivability of Organic Materials During Imact” was addressed. Her team did simulations of a1 km sphere of pure water impacting the Earth and a variety of angles. They studied the peak temperature of the material during impact, how the water behaves, and estimated final temperature ejected material that made it to (and stayed on) Earth.

Their simulations used the Lawrence Livermore Labs GEODYN Hydrocode. They found that for a 11.2km/s of a impact, pretty much nothing stayed a temperatures that would allow life (this is a head on collision, and really, those are bad). At more oblique angles, such as 30 degrees between ground and impact and 15 degrees the ejecta are cooler with a higher area of material distribution.

She did some neat things with her simulation. One movie she showed traced just the location of liquid water in the impacting comet. You could see it space and  you can do things like “turn on” liquid water, showing only where materials at certain temperatures are distributed. The material is heated via both shock heating deceleration (largely frictional) heating. Based on conservation of Mass, Momentum and Energy, the model can sort out the amount of mass surviving at different temperatures. They found that with the lowest impact angles (15 degrees), 79% of the mass didn’t get lost (generally splashed back up at vaporized), and of this 25% of the material condensed, 55% was at temperatures <870K, and 44% <373K. This last fraction is most important. That 44% at <373K could carry organics – and life – on a comet successfully to the Earth’s surface. This surviving material is highly dispersed, often over 1000s of km.

Continuing the theme of impacts, the next talk looked at HCN class organic molecules from impacts. Presented by K. Hurosawa, new research found that oblique impacts (those with small angles between the ground and impact), produce fine grained impact fragments that actively interact with an ambient atmosphere due to aerodynamic ablation – this means there is a downrange moving vapor cloud from the impact that is filled with N2, CN C2 and C-rich organics layers in fragments. These layered grains can undergo surface organic material formation. To estimate the yield of HCN during impact, the team needed to look at CO2 densities, pressures, and other properties in vapor clouds. In large vapors, C, H, and N diffusion works more slowly, and high impact velocities are have a negative impact or organic molecule formation. In general, HCN is more stable at lower temperatures. The question is, during impacts can HCNs form? This team used lasers to simulate the energies of impact using laser ablation. The laser targeted sintered graphite targets in a gas mixture rich in N, C, H, and I think there was also O listed (slides are flying fast and furious). They found a HCN column density of 10 mol/m^2 spread over 10^2 km^2 for a Carbonaceous Chontrite impactor 300 m in diameter that is an oblique impactor. A large dispersion of fragments is required for efficient HCN production and this is possible with shallow impact angles. This process may cause a significant concentration of HCN on the Early Earth.

Bottom-line of the morning: Life has been around a long time and both comets and asteroids can deliver and/or create organics to the Earth’s surface.

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