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Scott M. McLennan

Distinguished Professor
Office: ESS 252
Phone: 631-632-8194
E-mail:  scott.mclennan @

B.Sc.(Hon), University of Western Ontario, 1975
M.Sc., University of Western Ontario, 1977
Ph.D., Australian National University, 1981
Research Fellow, Australian National University, 1981-1986
Faculty member at Stony Brook since 1987

Preserved within sedimentary rocks is a record of planetary history. At any time eroding sediments are providing a sampling of the exposed crust and are being influenced by the contemporaneous climate. Using sedimentary compositions, it is possible to evaluate the tectonic, climatic and geographic conditions under which a sedimentary rock was deposited. Since sediments are present throughout much of the geological histories of both Earth and Mars, it is possible to trace the evolution of the surfaces of these planets. For Mars, although considerable geochemical and mineralogical data for sedimentary rocks are returned from the various missions to that planet, no sedimentary materials are yet available for laboratory analysis on Earth. Accordingly, an additional approach to studying the Martian sedimentary rock cycle is through laboratory experiments that simulate sedimentary conditions on Mars.

The interests of Professor McLennan lie in evaluating the evolution of planetary crusts and surficial processes using the chemical composition of sedimentary rocks and laboratory experiments that simulate a variety of sedimentary processes. It is now clear that there have been active sedimentary environments operating on Mars, especially early in its history. Accordingly, through his involvement with various planetary missions to Mars, Professor McLennan is also involved with evaluating the chemical and mineralogical composition of Martian surface materials in terms of sedimentary provenance, sedimentary processes, and crustal evolution.

Recent research projects include the following:

1.  Mars Mission Support and Research

Professor McLennan is a member of the science teams for the 2011 Mars Science Laboratory mission (Curiosity rover) and the 2018 InSight Lander mission. His role is to support mission planning and operations and to carry out research using the most recently returned data from Mars. He is also on two instrument teams (PIXL and SuperCam) for the Mars2020 Perseverance rover mission. Professor McLennan formerly was a participating scientist on the 2003 Mars Exploration Rover (Spirit and Opportunity rovers) mission and 2001 Mars Odyssey Gamma Ray Spectrometer experiment. He has supervised a number student and post-doctoral collaborators on these missions.

2. Sedimentary Geochemistry on Mars

Chemical analyses of surface rocks (especially sedimentary rocks) and soils returned during the Viking, Pathfinder, Spirit, Opportunity, Phoenix and Curiosity missions, coupled with mineralogical and chemical data from a variety of orbital missions, provide important constraints on the geological history of Mars. Professor McLennan is currently carrying out research to evaluate these results in terms of crustal evolution and the various “source-to-sink” sedimentary processes that may have operated at the Martian surface during its history.

3. Geochemical Evolution of Planetary Crusts

The origin, composition and evolution of planetary crusts remains a long-standing research interest of Professor McLennan, summarized in the book (with S. R. Taylor), Pla netary Crusts: Their Composition, Origin, and Evolution (Cambridge), which won the Geoscience Information Society's 2010 Award for Best Reference Work. With the arrival of the InSight Lander at the surface of Mars in November 2018, Professor McLennan was selected as a Participating Scientist on that mission and began working with InSight geophysical data, coupled with orbital Gamma Ray Spectroscopy from the 2001 Mars Odyssey mission, to refine models for the composition of the Martian crust and mantle and to place the findings into the broader context of better understanding the nature and evolution of terrestrial planets and exoplanets.

Selected Publications

McLennan, S. M. (2020) Composition of planetary crusts and planetary differentiation. In: S. Fagents, T. K. P. Gregg and R. Lopes (Eds.) Planetary Volcanism Across the Solar System. Elsevier. (in press).

Banaerdt, W. B., Smrekar, S. et al. (including S. McLennan) (2020) Initial results from the InSight mission on Mars. Nature Geosci., 13, 183-189.

Wang, A., Yan, Y., Jolliff, B. L., McLennan, S. M., Wang, K., Shi, E. and Farrell, W. M. (2020) Chlorine release from common chlorides by martian dust activity. J. Geophys. Res. – Planets, 125, e2019JE006283.

McLennan, S. M., Grotzinger, J. P., Hurowitz, J. A. and Tosca N. J. (2019) The sedimentary cycle on early Mars. Ann. Rev. Earth Planet. Sci., 47, 91-118.

Jolliff, B. L., Mittlefehldt, D. W., Farrand, W. H., Knoll, A. H., McLennan, S. M. and Gellert, R. (2019) Mars Exploration Rover Opportunity: Water and other volatiles on ancient Mars. In: J. Filiberto and S. P. Schwenzer (Eds.) Volatiles in the Martian Crust. Elsevier (Amsterdam) pp. 285-328.

Zhao, Y.-Y. S., McLennan, S. M., Jackson, A. W. and Karunatillake, S. (2018) Photochemical controls on chlorine and bromine geochemistry at the Martian surface. Earth Planet. Sci. Lett. 497, 102-112.

McLennan, S. M. (2018) Lanthanide rare earths. In:  W. M. White (Ed.)  Encyclopedia of Geochemistry, 2 nd Ed .  Springer-Verlag (Switzerland), doi:10.1007/978-3-319-39193-9_96-1.

Hurowitz, J. A., Grotzinger, J. P., Fischer, W. W., Milliken, R. E., Stein, N., Vasavada, A. R., Blake, D. F., Dehouck, E., Eigenbrode, J. L., Fairen, A. G., Frydenvang, J., Gellert, R., Grant, J. A., Gupta, S., Herkenhoff, K. E., McLennan, S. M., Ming, D. W., Rampe, E. B., Schmidt, M. E., Siebach, K., Stack-Morgan, K., Sumner, D. Y. and Wiens, R. C. (2017) Redox stratification of an ancient lake in Gale Crater, Mars. Science, 356, eaah6849, doi:10.1126/science.aah6849.

Siebach, K. L., Baker, M. B., Grotzinger, J. P., McLennan, S. M., Gellert, R., Thompson, L. M. and Hurowitz, J. A. (2017) Sorting out compositional trends in sedimentary rocks of the Bradbury Group (Aeolus Palus), Gale Crater, Mars. J. Geophys. Res. – Planets, 122, doi:10.1002/2016JE005195.

Cino, C. D., Dehouck, E. and McLennan, S. M. (2017) Geochemical constraints on the presence of clay minerals in the Burns Formation, Meridiani Planum, Mars. Icarus, 281, 137-150.

Dehouck, E., McLennan, S. M., Sklute, E. C. and Dyar, M. D. (2017) Stability and fate of ferrihydrite during episodes of water/rock interactions on early Mars:  Experimental approach. J. Geophys. Res. – Planets, 122, doi:10.1002/2016JE005222.

McLennan, S. M., Anderson, R. B. and 48 others (2014) Elemental geochemistry of sedimentary rocks in Yellowknife Bay, Gale Crater, Mars. Science, 343, doi:10.1126/science.1244734.

Grotzinger, J P., Sumner, D. Y., Kah, L. C., Stack, K., Gupta, S., Edgar, L., Rubin, D., Lewis, K., Schieber, J., Mangold, N., Milliken, R., Conrad, P., DesMarais, D., Farmer, J., Siebach, K.,Calef III, F., Hurowitz, J., McLennan, S. M. and 52 others (2014) A habitable fluvio-lacustrine environment at Yellowknife Bay, Gale Crater, Mars. Science, 343, doi:10.1126/science.1242777.

Dehouck, E., McLennan, S. M., Meslin, P.-Y. and Cousin, A. (2014) Constraints on abundance, composition and nature of X-ray amorphous components of soils and rocks at Gale crater, Mars .  J. Geophys. Res. 119, 2640-2657, doi:10.1002/2014JE004716.

Zhao, Y.-Y. S., McLennan, S. M. and Schoonen, M. A. A. (2014) Behavior of bromide, chloride and phosphate during low temperature aqueous Fe(II) oxidation processes on Mars. J. Geophys. Res.-Planets, 119, doi:10.1002/2013JE004417.

McSween Jr., H. Y. and McLennan, S. M. (2014) Mars. In: H. D. Holland and K. Turekian, eds., Treatise on Geochemistry, 2 nd Ed .; Vol. 2, A. M. Davis, ed., Planets, Asteroids, Comets and The Solar System (Elsevier, Amsterdam) pp. 251-300.

Karunatillake, S., Zhao, Y.-Y. S., McLennan, S. M., Skok, J. R. and Button, N. E. (2013) Does Martian soil release reactive halogens to the atmosphere? Icarus, 226, 1438-1446.

Grotzinger, J. P., Hayes, A. G., Lamb, M. P. and McLennan, S. M. (2013) Sedimentary processes on Earth, Mars, Titan and Venus. In: S. J. Mackwell et al., eds., Comparative Climatology of Terrestrial Planets, pp. 439-472. Univ. Arizona Press, Tucson.

Johnson, C., McLennan, S. M., McSween, H. Y. and Summons, R. E. (2013) Smaller, better, more: Five decades of advances in geochemistry. In Bickford, M. E., ed. The Web of Geological Sciences: Advances, Impacts, and Interactions, Geol. Soc. Am. Spec Paper 500, 1-44, doi:10.1130/2013.2500(08).

McLennan, S. M. and Taylor, S. R. (2012) Geology, geochemistry and natural abundances of the rare earth elements. In: D. A. Atwood (Ed.) The Rare Earth Elements: Fundamentals and Applications. John Wiley & Sons (Chichester, UK), pp.1-19.

McLennan, S. M. (2012) Geochemistry of sedimentary processes on Mars. In: J. P. Grotzinger and R. E. Milliken (eds.) Mars Sedimentology, SEPM Spec. Publ. 102, 119-138.

McLennan, S. M., Sephton, M. A. and 20 others (2012) Planning for Mars Returned Sample Science:  Final report of the MSR End-to-End International Science Analysis Group (E2E-iSAG): A report requested by the Mars Exploration Program Analysis Group (MEPAG). Astrobiology, 12, 175-230.

Hahn, B. C., McLennan, S. M. and Klein, E. C. (2011) Martian surface heat production and crustal heat flow from Mars Odyssey gamma-ray spectrometry. Geophys. Res. Lett. 38, L14203, doi:10.1029/2011GL047345.

Karunatillake, S., McLennan, S. and Herkenhoff, K. (2010) Regional and grain size influences on the geochemistry of soil at Gusev Crater, Mars. J. Geophys. Res., 115, E00F04, doi:10.1029/2010JE003637.

King, P. L. and McLennan, S. M. (2010) Sulfur on Mars. Elements, 6, 107-112.

Taylor, S. R. and McLennan, S. M. (2009) Planetary Crusts: Their Composition, Origin, and Evolution. Cambridge University Press (Cambridge) 378pp.

Tosca, N. J. and McLennan, S. M. (2009) Experimental constraints on the evaporation of partially oxidized acid-sulfate waters at the martian surface. Geochim. Cosmochim. Acta, 73, 1205-1222.

Tosca, N. J., Knoll, A. H. and McLennan, S. M. (2008) Water activity and the challenge for life on early Mars. Science, 320, 1204-1207.

McLennan, S. M. and Grotzinger, J. P. (2008) The sedimentary rock cycle of Mars. In: J. F. Bell III (ed.) The Martian Surface: Composition, Mineralogy, and Physical Properties. Cambridge Univ. Press (Cambridge), pp. 541-577.

Tosca, N. J., McLennan, S. M., Dyar, M. D., Sklute, E. C. and Michel, F. M. (2008) Fe oxidation processes at Meridiani Planum and implications for secondary Fe mineralogy on Mars. J. Geophys. Res.,113, E05005, doi:10.1029/2007JE003019.

Hurowitz, J. A. and McLennan, S. M. (2007) A ~3.5 Ga record of water-limited, acidic conditions on Mars. Earth Planet. Sci. Lett., 260, 432-443.

McLennan, S. M., Taylor, S. R. and Hemming, S. R. (2006) Composition, differentiation, and evolution of continental crust: Constraints from sedimentary rocks and heat flow. In: M. Brown and T. Rushmer, eds. Evolution and Differentiation of the Continental Crust. Cambridge Univ. Press, pp. 92-134.

Tosca, N. J. and McLennan, S. M. (2006) Chemical divides and evaporite assemblages on Mars. Earth Planet. Sci. Lett. 241, 21-31.

McLennan, S. M., Bell III, J. F., Calvin, W. and 29 others (2005) Provenance and diagenesis of the evaporite-bearing Burns formation, Meridiani Planum, Mars. Earth Planet. Sci. Lett. 240, 95-121.

Tosca, N. J., McLennan, S. M. et al. (2005) Geochemical modeling of evaporation processes on Mars: Insight from the sedimentary record at Meridiani Planum. Earth Planet. Sci. Lett. 240, 122-148.

Hurowitz, J. A., McLennan, S. M., Tosca, N. J., Arvidson, R. E., Michalski, J. R., Ming, D. W., Schöder, C. and Squyres, S. W. (2005) In-situ and experimental evidence for acidic weathering on Mars. J. Geophys. Res. 111, E02S19, doi:10.1029/2005JE002515.

Tosca, N. J., McLennan, S. M., Lindsley, D. H. and Schoonen, M. A. A. (2004) Acid-sulfate weathering of synthetic Martian basalt: The acid fog model revisited. J. Geophys. Res., 109, E05003, doi:10.1029/2003JE002218.

Squyres, S. W., Grotzinger, J. P., Arvidson, R. E., Bell III, J. F., Christensen, P. R., Clark, B. C., Crisp, J. A., Farrand, W. H., Herkenhoff, K. E., Johnson, J. R., Klingelhöfer, G., Knoll, A. H., McLennan, S. M. and 5 others (2004) In-situ evidence for an ancient aqueous environment on Mars. Science, 306, 1709-1714.

McLennan, S. M. (2003) Sedimentary silica on Mars. Geology, 31, 315-318.

McLennan, S. M. (2001) Relationships between the trace element composition of sedimentary rocks and upper continental crust.  Geochem. Geophys. Geosys. 2, 2000GC000109.

McLennan, S. M. (2001) Crustal heat production and the thermal evolution of Mars. Geophys. Res. Lett., 28, 4019-4022.

McLennan, S. M., Bock, B., Compston, W., Hemming, S. R. and McDaniel, D. K. (2001) Detrital zircon geochronology of Taconian and Acadian foreland sedimentary rocks in New England. J. Sed. Res., 71, 305-317.

McLennan, S. M. (2000) Chemical composition of Martian soil and rock: Complex mixing and sedimentary transport. Geophys. Res. Lett., 27, 1335-1338.

Lev, S. M., McLennan, S. M. and Hanson, G. N. (1999) Mineralogic controls on REE mobility during black-shale diagenesis. J. Sed. Res., 69, 1071-1082.

Taylor, S. R. and McLennan, S. M. (1995) The geochemical evolution of the continental crust. Rev. Geophys. , 33, 241-265.

Hemming, S. R., McLennan, S. M. and Hanson, G. N. (1994) Lead isotopes as a provenance tool for quartz: Examples from plutons and quartzite, northeastern Minnesota. Geochim. Cosmochim. Acta, 58,4455-4464.

McLennan, S. M., Hemming, S., McDaniel, D. K. and Hanson, G. N. (1993) Geochemical approaches to sedimentation, provenance and tectonics. In: M. J. Johnsson and A. Basu (Eds.) Processes Controlling the Composition of Clastic Sediments. Geol. Soc. Amer. Spec. Paper 284, 21-40.

McLennan, S. M. (1993) Weathering and global denudation.  J. Geol. 101, 295-303.

McLennan, S.M., Taylor, S.R., McCulloch, M.T. and Maynard, J.B. (1990) Geochemical and Nd-Sr isotopic composition of deep sea turbidites: Crustal evolution and plate tectonic associations. Geochim. Cosmochim. Acta 54, 2015-2050.

McLennan, S.M. (1989) Rare earth elements in sedimentary rocks: Influence of provenance and sedimentary processes. Rev. Mineral. 21, 169-200.

Taylor, S. R. and McLennan, S. M. (1985). The Continental Crust: Its Composition and Evolution. Blackwell (Oxford), 312pp.

Externally Funded Research

"Sedimentary Petrology at Aeolis Mons: Provenance, Processes and Paleoclimates": NASA/JPL Mars Science Laboratory Participating Scientist Program (2012-2023)

 “InSight Geophysical Constraints on the Composition of the Martian Crust-Mantle System and Implications for Planetary Differentiation”: NASA/JPL InSight Participating Scientist Program (2018-2022)

“Mars 2020 SuperCAM Co-Investigator”: NASA/JPL (2016-2023).

“Mars 2020 PIXL Co-Investigator”: NASA/JPL (2020-2023)

Recent Students and Post-Doctoral Fellows

Dr. Rebecca Smith (Ph.D., Arizona State Univ.), Post-doctoral Fellow 2018-present

Laura Martínez Parro (Universidad Complutense de Madrid) “Heat Flow Constraints on the Geochemistry of the Martian Crust”, Visiting Ph.D. Student (Aug.-Nov., 2017).

Dr. Kirsten Siebach (Ph.D., Caltech), Post-doctoral Fellow 2016-2017.

Christie Cino, “Geochemical Constraints and Modeling on the Presence of Clay Minerals in the Burns Formation, Meridiani Planum, Mars”, B.S. Honors (2015).

Dr. Erwin Dehouck (Ph.D., Nantes), Post-doctoral Fellow 2013-2015.

Yu-yan (Sara) Zhao, "Trace Element (Ni, Zn, Cr) and Halogen Geochemistry During Surficial Processes on Mars", Ph.D. (2014).

Dr. Suniti Karunatillake (Ph.D., Cornell), Post-doctoral Fellow 2008-2011 (Assistant Professor, Louisiana State University).