Proteins persist longer in the fossil record than DNA, but the longevity, survival mechanisms and substrates remain contested. Here, we demonstrate the role of mineral binding in preserving the protein sequence in ostrich (Struthionidae) eggshell, including from the palaeontological sites of Laetoli (3.8 Ma) and Olduvai Gorge (1.3 Ma) in Tanzania. By tracking protein diagenesis back in time we find consistent patterns of preservation, demonstrating authenticity of the surviving sequences. Molecular dynamics simulations of struthiocalcin-1 and -2, the dominant proteins within the eggshell, reveal that distinct domains bind to the mineral surface. It is the domain with the strongest calculated binding energy to the calcite surface that is selectively preserved. Thermal age calculations demonstrate that the Laetoli and Olduvai peptides are 50 times older than any previously authenticated sequence (equivalent to ~16 Ma at a constant 10°C).DOI: http://dx.doi.org/10.7554/eLife.17092.001

Isoprene is the most abundant non-methane biogenic volatile organic compound (BVOC), but the processes governing secondary organic aerosol (SOA) formation from isoprene oxidation are only beginning to become understood and selective quantification of the atmospheric particulate burden remains difficult. Organic aerosol above a tropical rainforest located in Danum Valley, Borneo, Malaysia, a high isoprene emission region, was studied during Summer 2008 using Aerosol Mass Spectrometry and offline detailed characterisation using comprehensive two dimensional gas chromatography. Observations indicate that a substantial fraction (up to 15% by mass) of atmospheric sub-micron organic aerosol was observed as methylfuran (MF) after thermal desorption. This observation was associated with the simultaneous measurements of established gas-phase isoprene oxidation products methylvinylketone (MVK) and methacrolein (MACR). Observations of MF were also made during experimental chamber oxidation of isoprene. Positive matrix factorisation of the AMS organic mass spectral time series produced a robust factor which accounts for an average of 23% (0.18 μg m⁻³), reaching as much as 53% (0.50 μg m⁻³) of the total oraganic loading, identified by (and highly correlated with) a strong MF signal. Assuming that this factor is generally representative of isoprene SOA, isoprene derived aerosol plays a significant role in the region. Comparisons with measurements from other studies suggest this type of isoprene SOA plays a role in other isoprene dominated environments, albeit with varying significance

Abstract. The effect of photochemical ageing and initial precursor concentration on the composition and hygroscopic properties of secondary organic aerosol (SOA) formed during the chamber photo-oxidation of β-caryophyllene/NOx mixtures were investigated. Nucleation of β-caryophyllene SOA particles occurred almost immediately after oxidation was initiated and led to the formation of fresh SOA with a relatively simpler composition than has been reported for monoterpenes. The SOA yield values ranged from 9.5–26.7% and 30.4–44.5% using a differential mobility particle sizer (DMPS) and an aerosol mass spectrometer (AMS) mass based measurements, respectively. A total of 20 compounds were identified in the SOA by LC-MS/MS, with the most abundant compounds identified as β-caryophyllonic acid and β-caryophyllinic acid/β-nocaryophyllonic acid. The O:C and H:C elemental ratios of products identified in the condensed phase ranged from 0.20 to 1.00 and 1.00 to 2.00, with average values of 0.39 and 1.58, respectively. The increase in the O:C ratio was associated with a decrease in the saturation concentration of the identified compounds. The compounds identified in the lower initial concentration experiments were more oxidised compared to those that were found to be more abundant in the higher initial concentration experiments with average O:C ratios of 0.51 and 0.27, respectively. Photochemical ageing led to a more complex SOA composition with a larger contribution coming from lower molar mass, higher generation products, where both double bonds had been oxidised. This effect was more evident in the experiments conducted using the lower initial precursor concentration; a finding confirmed by the temporal behaviour of key organic mass fragment measured by an Aerosol Mass Spectrometer. Although the composition changed with both initial precursor concentration and ageing, this had no significant measurable effect on the hygroscopic properties of the SOA formed. The latter finding might have been influenced by the difference in pre-treatment of the semivolatile-containing particles prior to their measurements.

Abstract. The use of β-caryophyllene secondary organic aerosol particles as seeds for smog chamber simulations has been investigated. A series of experiments were carried out in the Manchester photochemical chamber as part of the Aerosol Coupling in the Earth System (ACES) project to study the effect of seed particles on the formation of secondary organic aerosol (SOA) from limonene photooxidation. Rather than use a conventional seed aerosol containing ammonium sulfate or diesel particles, a method was developed to use in-situ chamber generated seed particles from β-caryophyllene photo-oxidation, which were then diluted to a desired mass loading (in this case 4-13 µg m −3 ). Limonene was then introduced into the chamber and oxidised, with the formation of SOA seen as a growth in the size of oxidised organic seed particles from 150 to 325 nm mean diameter. The effect of the partitioning of limonene oxidation products onto the seed aerosol was assessed using aerosol mass spectrometry during the experiment and the percentage of m/z 44, an indicator of degree of oxidation, increased from around 5 to 8 %. The hygroscopicity of the aerosol also changed, with the growth factor for 200 nm particles increasing from less than 1.05 to 1.25 at 90 % RH. The detailed chemical composition of the limonene SOA could be extracted from the complex β-caryophyllene matrix using two-dimensional gas chromatography (GC × GC) and liquid chromatography coupled to mass spectrometry. High resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS) was used to determine exact molecuCorrespondence to: J. F. Hamilton (jfh2@york.ac.uk) lar formulae of the seed and the limonene modified aerosol. The average O:C ratio was seen to increase from 0.32 to 0.37 after limonene oxidation products had condensed onto the organic seed.

Isoprene is the most abundant non-methane biogenic volatile organic compound (BVOC), but the processes governing secondary organic aerosol (SOA) formation from isoprene oxidation are only beginning to become understood and selective quantification of the atmospheric particulate burden remains difficult. Organic aerosol above a tropical rainforest located in Danum Valley, Borneo, Malaysia, a high isoprene emission region, was studied during Summer 2008 using Aerosol Mass Spectrometry and offline detailed characterisation using comprehensive two dimensional gas chromatography. Observations indicate that a substantial fraction (up to 15% by mass) of atmospheric sub-micron organic aerosol was observed as methylfuran (MF) after thermal desorption. This observation was associated with the simultaneous measurements of established gas-phase isoprene oxidation products methylvinylketone (MVK) and methacrolein (MACR). Observations of MF were also made during experimental chamber oxidation of isoprene. Positive matrix factorisation of the AMS organic mass spectral time series produced a robust factor which accounts for an average of 23% (0.18 μg m⁻³), reaching as much as 53% (0.50 μg m⁻³) of the total oraganic loading, identified by (and highly correlated with) a strong MF signal. Assuming that this factor is generally representative of isoprene SOA, isoprene derived aerosol plays a significant role in the region. Comparisons with measurements from other studies suggest this type of isoprene SOA plays a role in other isoprene dominated environments, albeit with varying significance