Earliest land plants created modern levels of atmospheric oxygen

In the paper

“If instead we assume that buried early plant matter had C/P = 2,000, then given their productivity, even with no effect on weathering fluxes, this increases global organic carbon burial by ∼ 50%, δ 13 C by 1.1 ‰ , and atmospheric O2 by 0.27 PAL (Fig. 3, cyan).”

In the paper

“In the original COPSE model (10), predicted NPP only reaches ∼ 5% of today ' s value in the Late Ordovician and Silurian, but when we assume a stronger Late Ordovician phase of land colonization by nonvascular plants (following ref. 20; SI Materials and Methods ), then COPSE predicts global NPP 30 -40% of today (Fig. 3 A ), consistent with the detailed spatial model.”

What the sources say

• Not checked yetcites [10] source
• Not checked yetcites [20] Lenton TM, Crouch M, Johnson M, Pires N, Dolan L (2012) First plants cooled the Ordovician. Nat Geosci 5(2):86 -89. source

In the paper

“If we include in COPSE an effect of early plants on silicate weathering following ref. 20, assuming C/P = 1,000, this increases organic carbon burial by ∼ 35%, δ 13 C by 0.7 ‰ , and O2 by 0.18 PAL (Fig. 3, magenta).”

What the sources say

• Not checked yetcites [20] Lenton TM, Crouch M, Johnson M, Pires N, Dolan L (2012) First plants cooled the Ordovician. Nat Geosci 5(2):86 -89. source

In the paper

“In COPSE, this advent of early land plants alone, with no assumed effect on weathering fluxes, and assumed C/P = 1,000, increases total organic carbon burial by ∼ 25%, δ 13 C by 0.5 ‰ , and atmospheric O2 by 0.11 PAL (Fig. 3, blue).”

In the paper

“However, we estimate much higher global NPP (Fig. 2) and weathering potential (32).”

What the sources say

• Not checked yetcites [32] Porada P, et al. (2016) High potential for weathering and climate effects of nonvascular vegetation in the Late Ordovician. Nat Commun , 10.1038/ncomms12113. source

In the paper

“Predicted NPP is sensitive to variations in CO2 and climate (Fig. S1), ice sheet cover (Fig. S2), and O 2 (Table S2), but is consistently higher than the 4.3 GtC · y -1 (7% of today) estimated elsewhere (33).”

What the sources say

• Not checked yetcites [33] Edwards D, Cherns L, Raven JA (2015) Could land-based early photosynthesizing ecosystems have bioengineered the planet in mid-Palaeozoic times? Palaeontology 58(5): 803 -837. source

In the paper

“The mean moss biomass in the biotic microcosms was 14.390 mg”

In the paper

“Assuming that early plants caused a sustained 50% increase in phosphorus weathering relative to bulk rock dissolution, with C/P = 1,000, increases total organic carbon burial by ∼ 95%, δ 13 C by 2.2 ‰ , and O2 by 0.74 PAL (to 0.97 PAL at 417 Ma; Fig. 3, yellow).”

In the paper

“Varying the uplift and degassing forcing of the model within plausible bounds only causes ± 0.08 PAL variation in O2 about the initial state (Fig. S4), although it does cause the effect of the same early plant forcing scenario to range over + 0.4 to 1.0 PAL O2 (Table S4).”

In the paper

“The relatively high global NPP results obtained are consistent with present-day cryptogamic covers providing ∼ 7% of global NPP, despite making up only 1% of terrestrial vegetation by mass (90) and being restricted to relatively resource-poor habitats, while also operating in an atmosphere with a low CO2/O2 ratio.”

What the sources say

• Not checked yetcites [90] Elbert W, et al. (2012) Contribution of cryptogamic covers to the global cycles of carbon and nitrogen. Nat Geosci 5(7):459 -462. source

In the paper

“Our model makes additional predictions that can be tested against geochemical data -notably, it predicts a decline in pyrite sulfur burial and associated drop in δ 34 S and increases in seawater SO4 concentration and C/S burial ratio with the rise of the earliest plants (Fig. S5).”

In the paper

“Assuming that buried early plant matter had a higher C/P = 2,000 causes larger increases in total organic carbon burial ∼ 60%, δ 13 C + 1.2 ‰ , and atmospheric O2 + 0.35 PAL (Fig. 3, green).”

In the paper

“the amplification factors for Ca = 1.4 and Mg = 1.5 from granite”

In the paper

“Including an additional negative feedback on O2, from increased marine organic C/P burial ratios under anoxic waters (37), increases its initial early Paleozoic level to 0.54 PAL and reduces the effect of the same biological forcing scenarios on O2 by ∼ 10 -30%, giving a maximum increase of + 0.63 PAL (Table S5).”

What the sources say

• Not checked yetcites [37] Van Cappellen P, Ingall ED (1996) Redox stabilization of the atmosphere and oceans by phosphorus-limited marine productivity. Science 271:493 -496. source

In the paper

“Assuming a sustained 25% increase in phosphorus weathering relative to bulk rock and C/P = 2,000 increases organic carbon burial by ∼ 90%, δ 13 C by 2.1 ‰ , and O2 by 0.67 PAL (Fig. 3, red).”

In the paper

“which assuming 0.43 gC/g biomass and C/P = 2,000 (Table S3) suggests 0.26 μ mol P in biomass, or for C/P = 1,000 -4,000, 0.13 -0.52 μ mol P in biomass”

In the paper

“Subsequent experiments (21) with the modern liverwort Marchantia paleacea found a 2.5- to 7-fold amplification of Ca weathering and a 9- to 13-fold amplification of P weathering from basalt.”

What the sources say

• Not checked yetcites [21] Quirk J, et al. (2015) Constraining the role of early land plants in Palaeozoic weathering and global cooling. Proc Biol Sci , 10.1098/rspb.2015.1115.

In the paper

“Furthermore, Early Devonian coaly shales indicate extensive peatlands 410 -400 Ma and have C/N of 44 -119 (28), comparable to that in modern peatlands where N/P and C/P ratios tend to increase with depth to C/P > 3,000 (34).”

What the sources say

• Not checked yetcites [28] Kennedy KL, et al. (2013) Lower Devonian coaly shales of northern New Brunswick, Canada: Plant accumulations in the early stages of Terrestrial colonization. J Sediment Res 83(12):1202 -1215. source
• Not checked yetcites [34] Wang M, Moore TR, Talbot J, Richard PJH (2014) The cascade of C:N:P stoichiometry in an ombrotrophic peatland: from plants to peat. Environ Res Lett 9(2):024003. source

In the paper

“The evolution of land plants is the obvious candidate”

In the paper

“Here we show that neither scenario is correct.”

In the paper

“However, plants and their associated mycorrhizal fungi can increase phosphorus weathering (20 -22), and this could be sustained on longer timescales if they preferentially weather phosphorus relative to alkalinity.”

What the sources say

• Not checked yetcites [20] Lenton TM, Crouch M, Johnson M, Pires N, Dolan L (2012) First plants cooled the Ordovician. Nat Geosci 5(2):86 -89. source
• Not checked yetcites [21] Quirk J, et al. (2015) Constraining the role of early land plants in Palaeozoic weathering and global cooling. Proc Biol Sci , 10.1098/rspb.2015.1115.
• Not checked yetcites [22] Lenton TM, Watson AJ (2000b) Redfield revisited: 2. What regulates the oxygen content of the atmosphere? Global Biogeochem Cycles 14(1):249 -268. source

In the paper

“The COPSE model we adapt here (10) predicts Early Paleozoic pO2 ∼ 0.2 -0.5 PAL consistent with redox proxy data but, like the other models (7, 8), it does not predict a rise in oxygen until the advent of forests starting ∼ 385 Ma, and continuing until ∼ 300 Ma, which is too late to explain marked changes in geochemical data that occur before ∼ 390 Ma (Fig. 1).”

What the sources say

• Not checked yetcites [10] source

In the paper

“Given that earlier plants developed peatlands (28), and had rock-weathering capabilities (20, 21), they could also have affected the global carbon cycle (18, 20).”

What the sources say

• Not checked yetcites [28] Kennedy KL, et al. (2013) Lower Devonian coaly shales of northern New Brunswick, Canada: Plant accumulations in the early stages of Terrestrial colonization. J Sediment Res 83(12):1202 -1215. source
• Not checked yetcites [20] Lenton TM, Crouch M, Johnson M, Pires N, Dolan L (2012) First plants cooled the Ordovician. Nat Geosci 5(2):86 -89. source
• Not checked yetcites [21] Quirk J, et al. (2015) Constraining the role of early land plants in Palaeozoic weathering and global cooling. Proc Biol Sci , 10.1098/rspb.2015.1115.

In the paper

“Though there are many subsequent δ 13 C fluctuations, including drops back to 0 ‰ , for example, at ∼ 400 Ma, the long-term mean δ 13 C remains ∼ 2 ‰ throughout the rest of the Paleozoic, the Mesozoic, and the Early Cenozoic (17), indicating a sustained increase in global organic carbon burial.”

What the sources say

• Not checked yetcites [17] Saltzman MR, Thomas E (2012) Carbon isotope stratigraphy. The Geologic Time Scale , eds Gradstein FM, Schmitz JGOD, Ogg GM (Elsevier, Boston), pp 207 -232. source

In the paper

“The persistent oxygenation of the ocean and appearance of charcoal can be explained by a rise in atmospheric oxygen occurring by ∼ 400 Ma”

In the paper

“Land plants typically have a much higher molar C/P ratio ( ∼ 1,000) than marine organic matter ( ∼ 100) due to carbon-rich but phosphorus-poor structural compounds such as sporopollenin, lignin, and, in their fungal mycorrhizal symbionts, chitin; therefore, they can support an increased organic carbon burial flux for the same P weathering flux.”

In the paper

“The P weathering flux is partly tied to bulk silicate weathering, for example, due to the dissolution of apatite inclusions in silicate rocks, and the silicate weathering flux of alkalinity is in turn set by negative feedback in the longterm carbon cycle, so is ultimately controlled by the degassing input of CO2 on timescales ≥ 1 My (7, 10).”

What the sources say

• Not checked yetcites [7] source
• Not checked yetcites [10] source

In the paper

“Instead, the earliest plants, which colonized the land from 470 Ma onward, first increased atmospheric oxygen to present levels by 400 Ma, and this instigated fire-mediated feedbacks that have stabilized high oxygen levels ever since, shaping subsequent evolution.”

In the paper

“This ocean oxygenation is also supported by a Silurian increase in the C/S ratio of shales (15), and a shift in iron speciation data sometime during 435 -387 Ma (6).”

What the sources say

• Not checked yetcites [15] Berner RA, Raiswell R (1983) Burial of organic carbon and pyrite sulfur in sediments over phanerozoic time: A new theory. Geochim Cosmochim Acta 47(5):855 -862. source
• Not checked yetcites [6] source

In the paper

“The early charcoal record (Table S1) was compiled from the literature (11, 12, 28, 44 -72) using existing compilations (12, 44 -47) and checking them where possible against the original sources.”

What the sources say

• Not checked yetcites [11] source
• Not checked yetcites [12] source
• Not checked yetcites [28] Kennedy KL, et al. (2013) Lower Devonian coaly shales of northern New Brunswick, Canada: Plant accumulations in the early stages of Terrestrial colonization. J Sediment Res 83(12):1202 -1215. source

In the paper

“This finding is broadly consistent with the sulfur isotope ( δ 34 S) record (38 -40), which shows a marked decline through the Silurian -Early Devonian from ∼ 30 to ∼ 18 ‰ , although available data also suggest an earlier Late Ordovician -Early Silurian rise from ∼ 25 to ∼ 30 ‰ , which the present model does not capture.”

What the sources say

• Not checked yetcites [38] Prokoph A, Shields GA, Veizer J (2008) Compilation and time-series analysis of a marine carbonate δ 18O, δ 13C, 87Sr/86Sr and δ 34S database through Earth history. Earth Sci Rev 87(3 -4):113 -133. source
• Not checked yetcites [39] Gill BC, Lyons TW, Saltzman MR (2007) Parallel, high-resolution carbon and sulfur isotope records of the evolving Paleozoic marine sulfur reservoir. Palaeogeogr Palaeoclimatol Palaeoecol 256(3 -4):156 -173. source
• Not checked yetcites [40] Jones DS, Fike DA (2013) Dynamic sulfur and carbon cycling through the end-Ordovician extinction revealed by paired sulfate -pyrite δ 34S. Earth Planet Sci Lett 363: 144 -155. source

In the paper

“Sensitivity analyses ( SI Materials and Methods ) indicate that our results are robust.”

In the paper

“Uncertainties shown in Fig. 1 represent 2 SD of the mean (analytical precision) plus the propagated uncertainty from matching in-house reference materials to the universal standard NIST SRM 3136 where seawater display δ 98/95 Mo = 2.3 ‰ (75, 76).”

What the sources say

• Not checked yetcites [75] Goldberg T, et al. (2013) Resolution of inter-laboratory discrepancies in Mo isotope data: An intercalibration. J Anal At Spectrom 28(5):724 -735. source
• Not checked yetcites [76] Nägler TF, et al. (2014) Proposal for an international molybdenum isotope measurement standard and data representation. Geostand Geoanal Res 38(2):149 -151. source

In the paper

“The δ 13 C record suggests this increase in organic carbon burial was essentially permanent, producing a new dynamically stable state for atmospheric O2.”

In the paper

“new fire-mediated negative feedbacks on O2 were instigated that have played a key role in stabilizing atmospheric O2 concentration up to the present day (22, 43).”

What the sources say

• Not checked yetcites [22] Lenton TM, Watson AJ (2000b) Redfield revisited: 2. What regulates the oxygen content of the atmosphere? Global Biogeochem Cycles 14(1):249 -268. source
• Not checked yetcites [43] Kump LR (1988) Terrestrial feedback in atmospheric oxygen regulation by fire and phosphorus. Nature 335:152 -154. source

In the paper

“The model is consistent with proxy reconstructions of seawater SO4 concentration, which suggest an Ordovician -Silurian rise from ∼ 6 to ∼ 10 mM (41), and with a Silurian increase in the molar C/S ratio of shales from ∼ 5 to ∼ 16 (15).”

What the sources say

• Not checked yetcites [41] Algeo TJ, Luo GM, Song HY, Lyons TW, Canfield DE (2015) Reconstruction of secular variation in seawater sulfate concentrations. Biogeosciences 12(7):2131 -2151. source
• Not checked yetcites [15] Berner RA, Raiswell R (1983) Burial of organic carbon and pyrite sulfur in sediments over phanerozoic time: A new theory. Geochim Cosmochim Acta 47(5):855 -862. source

In the paper

“We explored the sensitivity of predicted global NPP to variations in atmospheric CO2 and corresponding climate state (Fig. S1), to constraining vegetation cover with extensive Late Ordovician ice sheet cover (Fig. S2), and to varying O2 in combination with CO2 (Table S2).”

In the paper

“In this new steady state, oxidative weathering was increased (becoming less sensitive to variations in O2)”

In the paper

“In our previously reported (20) weathering experiments with granite, the mean amounts of phosphate weathered into aqueous solution were as follows: control microcosms = 0.0137 μ mol P, biotic microcosms = 0.0726 μ mol P.”

What the sources say

• Not checked yetcites [20] Lenton TM, Crouch M, Johnson M, Pires N, Dolan L (2012) First plants cooled the Ordovician. Nat Geosci 5(2):86 -89. source

In the paper

“Then, in a sensitivity analysis, we considered uncertainty in geologic forcing (91), and alternative initial conditions (altering the feedback structure of the model).”

What the sources say

• Not checked yetcites [91] Royer DL, Donnadieu Y, Park J, Kowalczyk J, Goddéris Y (2014) Error analysis of CO2 and O2 estimates from the long-term geochemical model GEOCARBSULF. Am J Sci 314(9):1259 -1283. source