Muons penetrate much further than X-rays, they do essentially zero damage, and they are provided for free by the cosmos.
Image credit: Science Source/Digital Globe.
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Edited by Robert A. Berner, Yale University, New Haven, CT, and approved August 6, 2002 (received for review May 21, 2002)
Article Figures & SI
Figures
- Figure 1
Relationship between SI (fraction of epidermal cells that are stomata) and atmospheric CO2 partial pressure of different tropical populations of L. cernuum. Solid line denotes the linear regression, dotted lines indicate the ±95% confidence limits. Central America (●), South America (□), and Asia (●) (n = 21, r2 = 0.73, P < 0.01). All leaves were obtained from the herbarium of the Natural History Museum, London. SI measurements were made on cleared leaves (n = 5–8 per date) of each species collected over the past 150 years of CO2 increase. Corresponding mean global atmospheric CO2 concentrations were determined from ice core studies (13) or instrumental records (available at http://cdiac.esd.ornl.gov), after appropriate correction for altitude.
- Figure 2
Comparison of the carbon isotope discrimination (▵) of modern (□) and extinct (■) lycopsids. Each box delineates the 25th and 75th percentiles, errors bars show the fifth and 95th percentiles, the horizontal line represents the median value of the sample set. Δ calculated for herbarium leaf sequences of L. cernuum (Central America populations, n = 9, 1868–1995; South American populations, n = 8, 1853 – 1987; Asian populations, n = 12, 1822–1981). Changes in Δ were not correlated with historical atmospheric CO2 increase in the extant lycopsid species. Therefore, intraspecific variations reflect differences in microhabitats and interannual climate fluctuations.
- Figure 3
Late Palaeozoic evidence for ice (summarized from refs. 23, 25, and 27) and atmospheric CO2 concentrations reconstructed from paleosols and predicted by a geochemical model of the long-term global carbon cycle (solid line). Red boxes indicate CO2 estimates from the current study. The dashed horizontal line indicates the threshold atmospheric CO2 level above which theoretical studies predict deglaciation on Pangea and the maintenance of an ice-free state (24).
Tables
- Table 1
Stomatal characteristics of fossil Carboniferous (C) and Permian (P) lycopsid microphyll leaves and leaf bases
Fossil specimen Period Stage Age, Myr ago Organ SI*, % Atmospheric CO2 concentration (ppm) ± 95% cls Lepidodendron rhodianum C Namurian 331–318 Leaf scars 4.9 385 ± 
L. veltheimii C Namurian 331–318 Leaf cushions 4.0 392 ± Lepidophloios grangeri C Namurian 331–318 Leaf cushions 8.1 359 ± Bothrodendron minutifolium C Westphalian 318–303 Leaves 9.4 348 ± Lepidodendron aculeatum C Westphalian 318–303 Leaf cushions 9.0 351 ± L. arberi C Westphalian 318–303 Leaf cushions 10.9 336 ± L. dichotomum C Westphalian 318–303 Leaf cushions 14.4 308 ± L. feistmantelii C Westphalian 318–303 Leaf cushions 9.2 350 ± L. mannabachense C Westphalian 318–303 Leaf scars 7.3 366 ± L. peachii C Westphalian 318–303 Leaf scars 6.9 368 ± L. subdichotomum C Westphalian 318–303 Leaf cushions 8.2 358 ± Lepidophloios acadianus C Westphalian 318–303 Leaf cushions 15.0 303 ± L. acerosus C Westphalian 318–303 Leaf cushions 7.1 367 ± L. laricinus C Westphalian 318–303 Leaf cushions 9.2 350 ± L. macrolepidotus C Westphalian 318–303 Leaf cushions 2.9 401 ± Ulodendron landsbergii C Westphalian 318–303 Leaf cushions 17.0 287 ± U. landsbergii C Westphalian 318–303 Leaves 14.0 311 ± U. majus C Westphalian 318–303 Leaf cushions 17.3 284 ± U. majus C Westphalian 318–303 Leaves 12.3 325 ± Synchysidendron sp. P Kazanian 268 Leaf cushions 10.1 342 ± Paralycopodites sp. P Kazanian 266 Leaf cushions 12.1 326 ± Dispersed cuticles P Kazanian 263 Leaf cushions (?) 16.6 290 ± Synchysidendron baodeense P Kazanian 260 Leaf cushions 10.1 343 ± Dispersed cuticles P Kazanian 260 Leaf cushions (?) 19.6 266 ± -
↵* Calculated as (SD/(SD + ED) × 100), where SD is stomatal density (mm−2), measured directly on fossil cuticles, and ED is epidermal cell density, calculated from cell dimensions for the Carboniferous plant cuticles.
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- Table 2
Carbon isotope characteristics of Carboniferous compression fossil lycopsid shoots
Fossil specimen Specimen number Organ δpcorr, ‰ Δ, ‰ ci/ca, unitless Bothrodendraceae Bothrodendron minutifolium RC2872 Leafy shoot −23.5 22.0 0.78 B. minutifolium 51813 Leafy shoot −24.0 22.5 0.80 B. minutifolium 1292 Leafy shoot −23.4 21.9 0.77 B. minutifolium 1300 Leafy shoot −22.9 21.4 0.75 B. minutifolium 1201 Leafy shoot −23.6 22.1 0.78 Lepidodendraceae Lepidostrobophyllum alatum RC4838 Reproductive shoot −23.1 21.6 0.76 L. lanceolatum RC3134 Reproductive shoot −22.9 21.4 0.75 Lepidophyllum sp. 6127 Reproductive shoot −23.0 21.5 0.76 Lepidodendron ophiurus 5284 Leafy shoot −23.3 21.8 0.77 L. lanceolatum JP218 Leafy shoot −23.9 22.4 0.80 L. lycopodioides 18239 Leafy shoot −23.2 21.7 0.77 Lepidostrobus sp. 6276 Reproductive shoot −24.1 22.6 0.81 Sigillariaceae Sigillariostrobus rhombibracteatus 1177 Cone −23.0 21.5 0.76 Sigillariostrobus sp. 1656 Cone −23.7 22.2 0.79 Sigillaria mamillaris RC2875 Leafy shoot −22.7 21.2 0.74 Other lycopsids Cyperites bicarinatus 4907 Leafy shoot −24.7 23.3 0.84 C. bicarinatus RG4477 Leafy shoot −24.3 22.9 0.80 C. ciliatum 76313 Leafy shoot −24.5 23.1 0.83 -
All specimens are of Westphalian age (303–318 Myr BP) and held at the British Geological Survey, Keyworth, United Kingdom.
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Low atmospheric CO2 levels during the Permo- Carboniferous glaciation inferred from fossil lycopsids
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