2: Earth Formation and Structure - Geosciences
- 2.1: Early Earth
- Earth in its early stages was like a depiction of hell, scalding rock and choking fumes, due to accretion from cosmic debris. The surface was essentially a magma ocean, much too harsh of conditions for anything to survive. Some water and a very early atmosphere was present, and crustal rocks began to form. But the mantle was convecting and volcanism was intense. Large asteroids kept falling in, producing craters and an overall large-scale disturbance.
- 2.2: Structure of the Earth
- The structure of the earth has been classically divided into four major groups. The crust, the mantel, and the outer and inner cores have all been defined by their unique chemical properties based off of studies of volcanic and seismic activity as well as mass estimates of the earth that have been able to determine the densities of the different layers. The way these layers interact with each other has significant implications to volcanic, seismic, and electromagnetic activity.
- 2.3: Continental Drift
- Continental drift was first conceived by scholars and philosophers named Francis Bacon, George Buffon, and Alexander von Humboldt. As maps grew more accurate the landmasses began appeared as puzzle pieces. The continents once had fit together but had drifted apart after millions of years. The continents now far apart showed similar sediment, rock formation, and vegetation supporting the theory that they were one landmass in the past.
- 2.4: Evidence for Plate Tectonics
- 2.5: Types of Plate Boundaries
- Categorization of plate boundaries is based off of how two plates move relative to each other. There are essentially three types of plate boundaries, which are divergent, convergent, and transform.
- 2.6: Continental Margins and Ocean Basins
- 2.7: Summary
Thumbnail: Diagram of the Earth. (CC-SA-BY 3.0; Kelvinsong).
Bachelor's Degree Programme Geosciences
Are you fascinated by our planet? Would like to explore it more closely? Do you enjoy working and carrying out experiments outdoors? In the bachelor's degree programme Geosciences, you will learn how the Earth and all its lifeforms have developed over the last 4.5 billion years. This allows you to benefit from accessing offers from two excellent universities: TU Graz and the University of Graz.
The Earth’s crust contains structures almost everywhere, and the aims of structural geology are to document and understand these structures. In general, work in structural geology is targeted at three different aims, or levels of understanding.
- Descriptive or Geometric analysis – what are the positions, orientations, sizes and shapes of structures that exist in the Earth’s crust at the present day?
- Kinematic analysis – what changes in position, orientation, size, and shape occurred between the formation of the rocks and their present-day configuration? Together, these changes are called deformation . Changes in size and shape are called strain strain analysis is a special part of kinematic analysis.
- Dynamic analysis – what forces operated and how much energy was required to deform the rocks into their present configuration? Most often in dynamic analysis we are interested in how concentrated the forces were. Stress , or force per unit area, is a common measure of force concentration used in dynamic analysis.
It is important to keep these three distinct. In particular, make sure you can describe structures first, before attempting to figure out what moved where, and avoid jumping to conclusions about force or stress without first understanding both the geometry and the kinematics of the situation.
Much of this book will focus on the descriptive or geometric objective, which is a foundation for further understanding. Once you have thoroughly described structures, you will be able to proceed to kinematic and sometimes dynamic conclusions.
Historical development of alternative conceptions
In 1692 Edmund Halley (in a paper printed in Philosophical Transactions of Royal Society of London) put forth the idea of Earth consisting of a hollow shell about 500 miles thick, with two inner concentric shells around an innermost core, corresponding to the diameters of the planets Venus, Mars, and Mercury respectively. [ 16] Halley's construct was a method of accounting for the (flawed) values of the relative density of Earth and the Moon that had been given by Sir Isaac Newton, in Principia (1687). "Sir Isaac Newton has demonstrated the Moon to be more solid than our Earth, as 9 to 5, " Halley remarked "why may we not then suppose four ninths of our globe to be cavity?" [ 16]
Our home planet Earth is a rocky, terrestrial planet. It has a solid and active surface with mountains, valleys, canyons, plains and so much more. Earth is special because it is an ocean planet. Water covers 70 percent of Earth's surface.
Earth's atmosphere is made mostly of nitrogen and has plenty of oxygen for us to breathe. The atmosphere also protects us from incoming meteoroids, most of which break up before they can hit the surface.
Visit NASA Space Place for more kid-friendly facts .
Like Mars and Venus, Earth has volcanoes, mountains and valleys. Earth's lithosphere, which includes the crust (both continental and oceanic) and the upper mantle, is divided into huge plates that are constantly moving. For example, the North American plate moves west over the Pacific Ocean basin, roughly at a rate equal to the growth of our fingernails. Earthquakes result when plates grind past one another, ride up over one another, collide to make mountains, or split and separate.
Earth's global ocean, which covers nearly 70 percent of the planet's surface, has an average depth of about 2.5 miles (4 kilometers) and contains 97 percent of Earth's water. Almost all of Earth's volcanoes are hidden under these oceans. Hawaii's Mauna Kea volcano is taller from base to summit than Mount Everest, but most of it is underwater. Earth's longest mountain range is also underwater, at the bottom of the Arctic and Atlantic oceans. It is four times longer than the Andes, Rockies and Himalayas combined.
Near the surface, Earth has an atmosphere that consists of 78 percent nitrogen, 21 percent oxygen, and 1 percent other gases such as argon, carbon dioxide and neon. The atmosphere affects Earth's long-term climate and short-term local weather and shields us from much of the harmful radiation coming from the Sun. It also protects us from meteoroids, most of which burn up in the atmosphere, seen as meteors in the night sky, before they can strike the surface as meteorites.
Our planet's rapid rotation and molten nickel-iron core give rise to a magnetic field, which the solar wind distorts into a teardrop shape in space. (The solar wind is a stream of charged particles continuously ejected from the Sun.) When charged particles from the solar wind become trapped in Earth's magnetic field, they collide with air molecules above our planet's magnetic poles. These air molecules then begin to glow and cause aurorae, or the northern and southern lights.
The magnetic field is what causes compass needles to point to the North Pole regardless of which way you turn. But the magnetic polarity of Earth can change, flipping the direction of the magnetic field. The geologic record tells scientists that a magnetic reversal takes place about every 400,000 years on average, but the timing is very irregular. As far as we know, such a magnetic reversal doesn't cause any harm to life on Earth, and a reversal is very unlikely to happen for at least another thousand years. But when it does happen, compass needles are likely to point in many different directions for a few centuries while the switch is being made. And after the switch is completed, they will all point south instead of north.
Earth is the only planet that has a single moon. Our Moon is the brightest and most familiar object in the night sky. In many ways, the Moon is responsible for making Earth such a great home. It stabilizes our planet's wobble, which has made the climate less variable over thousands of years.
Earth sometimes temporarily hosts orbiting asteroids or large rocks. They are typically trapped by Earth's gravity for a a few months or years before returning to an orbit around the Sun. Some asteroids will be in a long &ldquodance&rdquo with Earth as both orbit the Sun.
Some moons are bits of rock that were captured by a planet's gravity, but our Moon is likely the result of a collision billions of years ago. When Earth was a young planet, a large chunk of rock smashed into it, displacing a portion of Earth's interior. The resulting chunks clumped together and formed our Moon. With a radius of 1,080 miles (1,738 kilometers), the Moon is the fifth largest moon in our solar system (after Ganymede, Titan, Callisto and Io).
The Moon is farther away from Earth than most people realize. The Moon is an average of 238,855 miles (384,400 kilometers) away. That means 30 Earth-sized planets could fit in between Earth and the Moon.
Potential for Life
Earth has a very hospitable temperature and mix of chemicals that have made life possible here. Most notably, Earth is unique in that most of our planet is covered in water, since the temperature allows liquid water to exist for extended periods of time. Earth's vast oceans provided a convenient place for life to begin about 3.8 billion years ago.
Chapter 7: Chapter Challenge
In this section you will find materials that support the implementation of EarthComm, Chapter 7: Chapter Challenge.
Evolution of the Earth System
The Archaen Eon and Hadean, Univ. of California Museum of Paleontology
Brief overview of Earth’s early formation.
Impact Processes on the Early Earth, Univ. of Vienna
Describes the impact processes that occurred during the period of late heavy bombardment.
Earth’s Formation and its Interior Structure, University of Wisconsin-Madison
Overview of Earth’s formation, including the bombardment by meteoric debris.
Evolution of Continents and Oceans, Indiana University
Overview of the processes that form new crust and consume old crust. Also looks at the evolution and features of continental crust, including shields and platforms.
The Precambrian Era, Michigan State University
Describes the geologic history of Earth, including its formation and the evolution of its early crust.
The Evolution of Continental Crust, University of Washington
Examines the conditions required for the formation of continents. Compares the planets and the extent to which those conditions exist.
The Magnetosphere: Our Shield in Space, NASA
Describes Earth’s magnetic field and its relationship to solar wind.
Origin of the Earth's Atmosphere, Eastern Illinois University
Describes the compositions of Earth’s atmospheres and how they were produced.
How did Earth’s atmosphere and oceans form?, The University of Michigan
Looks at Earth’s early atmosphere and how it was formed by the release of gases trapped in Earth’s interior.
The Carbon Cycle and Earth's Climate, Columbia University
Describes the cycling of carbon through the Earth system and the role carbon plays in the weathering of rocks.
Banded Iron Formation, University of Oregon
Examines the formation of banded iron formations.
From Soup to Cells—the Origin of Life, University of California Museum of Paleontology
Looks at the evidence of Earth’s earliest life forms. Considers where and how life originated.
How did life originate?, University of California Museum of Paleontology
Examines the series of steps that led to the formation of multicellular life forms.
Studying the origin of life, University of California Museum of Paleontology
Considers the role of RNA and DNA in the evolution of living things.
Origin of Life: The Panspermia Theory, Sonali S. Joshi
Overview of the panspermia theory, which suggests that life on Earth was transported to Earth from somewhere else in the universe.
Origins of Life on Earth, Fulton-Montgomery Community College
Overview of various theories for how life on Earth originated and evolved to multicellular forms.
Cyanobacteria: Fossil Record, University of California Museum of Paleontology
Examines the formation of stromatolites from cyanobacteria and the fossil evidence they contain of early life forms.
Stromatolites, Carleton College
Overview of stromatolites. Includes several images of different stromatolite forms.
Geologic History, The Virtual Fossil Museum
Looks at the geologic time scale and major events that occurred in different periods.
Geologic Timeline, San Diego Natural History Museum
In-depth descriptions of common life forms present in the subdivisions of geologic time.
Mass Extinctions, Hooper Virtual Paleontological Museum
Provides a short discussion about mass extinctions.
Causes of Mass Extinctions, Penn State University
Detailed website offering information on the causes of extinctions and possible future events.
The Matlab files used for statistical distribution of the isotopic data are available from the corresponding author upon request.
Burke, K., Steinberger, B., Torsvik, T. H. & Smethurst, M. A. Plume generation zones at the margins of large low shear velocity provinces on the core–mantle boundary. Earth Planet. Sci. Lett. 265, 49–60 (2008).
Dziewonski, A. M., Lekic, V. & Romanowicz, B. A. Mantle anchor structure: an argument for bottom up tectonics. Earth Planet. Sci. Lett. 299, 69–79 (2010).
Li, Z.-X. & Zhong, S. Supercontinent–superplume coupling, true polar wander and plume mobility: plate dominance in whole-mantle tectonics. Phys. Earth Planet. Inter. 176, 143–156 (2009).
Anderson, D. L. Superplumes or supercontinents? Geology 22, 39–42 (1994).
Bunge, H.-P. et al. Time scales and heterogeneous structure in geodynamic Earth models. Science 280, 91–95 (1998).
McNamara, A. K. & Zhong, S. Thermochemical structures beneath Africa and the Pacific Ocean. Nature 437, 1136–1139 (2005).
Li, Z. X. et al. Assembly, configuration, and break-up history of Rodinia: a synthesis. Precambrian Res. 160, 179–210 (2008).
Mitchell, R. N., Kilian, T. M. & Evans, D. A. D. Supercontinent cycles and the calculation of absolute palaeolongitude in deep time. Nature 482, 208–211 (2012).
Evans, D. A. True polar wander, a supercontinental legacy. Earth Planet. Sci. Lett. 157, 1–8 (1998).
Gamal El Dien, H., Doucet, L. S., Li, Z.-X., Cox, M. C. & Mitchell, R. N. Global geochemical fingerprinting of plume intensity suggests coupling with the supercontinent cycle. Nat. Commun. 10, 5270 (2019).
Doucet, L. S. et al. Coupled supercontinent–mantle plume events evidenced by oceanic plume record. Geology 48, 159–163 (2020).
Jackson, M. G. et al. Evidence for the survival of the oldest terrestrial mantle reservoir. Nature 466, 853–856 (2010).
White, W. M. Isotopes, DUPAL, LLSVPs, and anekantavada. Chem. Geol. 419, 10–28 (2015).
Class, C. & Goldstein, S. L. Evolution of helium isotopes in the Earth’s mantle. Nature 436, 1107–1112 (2005).
Dupré, B. & Allègre, C. J. Pb–Sr isotope variations in Indian Ocean basalts and mixing phenomena. Nature 303, 142–146 (1983).
Hart, S. R. A large-scale anomaly in the Southern Hemisphere mantle. Nature 309, 753–757 (1984).
Staudigel, H. et al. The longevity of the South Pacific isotopic and thermal anomaly. Earth Planet. Sci. Lett. 102, 24–44 (1991).
Castillo, P. The Dupal anomaly as a trace of the upwelling lower mantle. Nature 336, 667–670 (1988).
Jackson, M., Becker, T. & Konter, J. Geochemistry and distribution of recycled domains in the mantle inferred from Nd and Pb isotopes in oceanic hot spots: implications for storage in the large low shear wave velocity provinces. Geochem. Geophys. Geosyst. 19, 3496–3519 (2018).
French, S. W. & Romanowicz, B. Broad plumes rooted at the base of the Earth’s mantle beneath major hotspots. Nature 525, 95–99 (2015).
Torsvik, T. H., Steinberger, B., Ashwal, L. D., Doubrovine, P. V. & Trønnes, R. G. Earth evolution and dynamics—a tribute to Kevin Burke. Can. J. Earth Sci. 53, 1073–1087 (2016).
Hager, B. H., Clayton, R. W., Richards, M. A., Comer, R. P. & Dziewonski, A. M. Lower mantle heterogeneity, dynamic topography and the geoid. Nature 313, 541–545 (1985).
Courtillot, V., Davaille, A., Besse, J. & Stock, J. Three distinct types of hotspots in the Earth’s mantle. Earth Planet Sci. Lett. 205, 295–308 (2003).
Jackson, M. G., Konter, J. G. & Becker, T. W. Primordial helium entrained by the hottest mantle plumes. Nature 542, 340–343 (2017).
Becker, T. W. & Boschi, L. A comparison of tomographic and geodynamic mantle models. Geochem. Geophys. Geosyst. 3, 1003 (2002).
Jackson, M. G. et al. The return of subducted continental crust in Samoan lavas. Nature 448, 684–687 (2007).
Boschi, L., Becker, T. & Steinberger, B. Mantle plumes: dynamic models and seismic images. Geochem. Geophys. Geosyst. 8, Q10006 (2007).
Druken, K., Kincaid, C., Griffiths, R., Stegman, D. & Hart, S. Plume–slab interaction: the Samoa–Tonga system. Phys. Earth Planet. Inter. 232, 1–14 (2014).
Cottaar, S. & Lekic, V. Morphology of seismically slow lower-mantle structures. Geophys. J. Int. 207, 1122–1136 (2016).
Bebout, G. E., Bebout, A. E. & Graham, C. M. Cycling of B, Li, and LILE (K, Cs, Rb, Ba, Sr) into subduction zones: SIMS evidence from micas in high-P/T metasedimentary rocks. Chem. Geol. 239, 284–304 (2007).
Rizo, H. et al. Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts. Science 352, 809–812 (2016).
Mundl, A. et al. Tungsten-182 heterogeneity in modern ocean island basalts. Science 356, 66–69 (2017).
Rizo, H. et al. 182 W evidence for core-mantle interaction in the source of mantle plumes. Geochemical Perspect. Lett. 11, 6–11 (2019).
Wang, X.-C. et al. Identification of an ancient mantle reservoir and young recycled materials in the source region of a young mantle plume: implications for potential linkages between plume and plate tectonics. Earth Planet. Sci. Lett. 377-378, 248–259 (2013).
Li, Z. X. et al. Decoding Earth’s rhythms: modulation of supercontinent cycles by longer superocean episodes. Precambrian Res. 323, 1–5 (2019).
Willbold, M. & Stracke, A. Formation of enriched mantle components by recycling of upper and lower continental crust. Chem. Geol. 276, 188–197 (2010).
Doubrovine, P. V., Steinberger, B. & Torsvik, T. H. A failure to reject: testing the correlation between large igneous provinces and deep mantle structures with EDF statistics. Geochem. Geophys. Geosyst. 17, 1130–1163 (2016).
Zindler, A. & Hart, S. Chemical geodynamics. Annu. Rev. Earth Planet Sci. 14, 493–571 (1986).
Matthews, K. J. et al. Global plate boundary evolution and kinematics since the late Paleozoic. Glob. Planet. Change 146, 226–250 (2016).
Le Bas, M. IUGS reclassification of the high-Mg and picritic volcanic rocks. J. Petrol. 41, 1467–1470 (2000).
Olierook, H. K., Jiang, Q., Jourdan, F. & Chiaradia, M. Greater Kerguelen large igneous province reveals no role for Kerguelen mantle plume in the continental breakup of eastern Gondwana. Earth Planet. Sci. Lett. 511, 244–255 (2019).
Botev, Z. I., Grotowski, J. F. & Kroese, D. P. Kernel density estimation via diffusion. Ann. Stat. 38, 2916–2957 (2010).
Spencer, C. J. et al. Deconvolving the pre-Himalayan Indian margin—tales of crustal growth and destruction. Geosci. Front. 10, 863–872 (2019).
Asmerom, Y. & Jacobsen, S. B. The Pb isotopic evolution of the Earth: inferences from river water suspended loads. Earth Planet. Sci. Lett. 115, 245–256 (1993).
Simmons, N. A., Forte, A. M., Boschi, L. & Grand, S. P. GyPSuM: a joint tomographic model of mantle density and seismic wave speeds. J. Geophys. Res. Solid Earth 115 (2010).
Houser, C., Masters, G., Shearer, P. & Laske, G. Shear and compressional velocity models of the mantle from cluster analysis of long-period waveforms. Geophys. J. Int. 174, 195–212 (2008).
Ritsema, J., Deuss, A. A., Van Heijst, H. & Woodhouse, J. S40RTS: a degree-40 shear-velocity model for the mantle from new Rayleigh wave dispersion, teleseismic traveltime and normal-mode splitting function measurements. Geophys. J. Int. 184, 1223–1236 (2011).
Kustowski, B., Ekström, G. & Dziewoński, A. Anisotropic shear‐wave velocity structure of the Earth’s mantle: a global model. J. Geophys. Res. Solid Earth 113 (2008).
Mégnin, C. & Romanowicz, B. The three‐dimensional shear velocity structure of the mantle from the inversion of body, surface and higher‐mode waveforms. Geophys. J. Int. 143, 709–728 (2000).
Müller, R. D., Royer, J.-Y. & Lawver, L. A. Revised plate motions relative to the hotspots from combined Atlantic and Indian Ocean hotspot tracks. Geology 21, 275–278 (1993).
Gibson, S., Thompson, R. & Day, J. Timescales and mechanisms of plume–lithosphere interactions: 40 Ar/ 39 Ar geochronology and geochemistry of alkaline igneous rocks from the Paraná–Etendeka large igneous province. Earth Planet. Sci. Lett. 251, 1–17 (2006).
Gibson, S., Thompson, R., Leonardos, O., Dickin, A. & Mitchell, J. The limited extent of plume–lithosphere interactions during continental flood-basalt genesis: geochemical evidence from Cretaceous magmatism in southern Brazil. Contrib. Mineral. Petrol. 137, 147–169 (1999).
Johansson, L., Zahirovic, S. & Müller, R. D. The interplay between the eruption and weathering of large igneous provinces and the deep‐time carbon cycle. Geophys. Res. Lett. 45, 5380–5389 (2018).
Hilton, D., Barling, J. & Wheller, G. Effect of shallow-level contamination on the helium isotope systematics of ocean-island lavas. Nature 373, 330–333 (1995).
Coffin, M. F. et al. Kerguelen hotspot magma output since 130 Ma. J. Petrol. 43, 1121–1137 (2002).
Doucet, S. et al. Primitive neon and helium isotopic compositions of high-MgO basalts from the Kerguelen Archipelago, Indian Ocean. Earth Planet Sci. Lett. 241, 65–79 (2006).
Storey, B. C. The role of mantle plumes in continental breakup: case histories from Gondwanaland. Nature 377, 301–308 (1995).
Graham, D., Lupton, J., Albarède, F. & Condomines, M. Extreme temporal homogeneity of helium isotopes at Piton de la Fournaise, Réunion Island. Nature 347, 545–548 (1990).
Stroncik, N., Niedermann, S., Schnabel, E. & Erzinger, J. Determining the geochemical structure of the mantle from surface isotope distribution patterns? Insights from Ne and He isotopes and abundance ratios. AGU Fall Meeting 2011 abstr. V51B-2519 (AGU, 2011).
Poreda, R., Schilling, J.-G. & Craig, H. Helium isotope ratios in Easter microplate basalts. Earth Planet. Sci. Lett. 119, 319–329 (1993).
Head, J. W. & Coffin, M. F. in Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism (eds Mahoney, J. J. & Coffin, M. F.) 411–438 (AGU, 1997).
Kurz, M. D., Jenkins, W. J., Hart, S. R. & Clague, D. Helium isotopic variations in volcanic rocks from Loihi Seamount and the Island of Hawaii. Earth Planet. Sci. Lett. 66, 388–406 (1983).
Kurz, M., Jenkins, W. & Hart, S. Helium isotopic systematics of oceanic islands and mantle heterogeneity. Nature 297, 43–47 (1982).
Olierook, H. K., Jourdan, F. & Merle, R. E. Age of the Barremian–Aptian boundary and onset of the Cretaceous Normal Superchron. Earth Sci. Rev. 197, 102906 (2019).
Graham, D. W. et al. Helium isotope composition of the early Iceland mantle plume inferred from the Tertiary picrites of West Greenland. Earth Planet Sci. Lett. 160, 241–255 (1998).
Storey, M., Duncan, R. A. & Tegner, C. Timing and duration of volcanism in the North Atlantic Igneous Province: implications for geodynamics and links to the Iceland hotspot. Chem. Geol. 241, 264–281 (2007).
Lawver, L. A. & Müller, R. D. Iceland hotspot track. Geology 22, 311–314 (1994).
Torsvik, T. H. et al. Continental crust beneath southeast Iceland. Proc. Natl Acad. Sci. USA 112, E1818–E1827 (2015).
Werner, R. et al. Drowned 14-my-old Galápagos archipelago off the coast of Costa Rica: implications for tectonic and evolutionary models. Geology 27, 499–502 (1999).
Jackson, M. G., Kurz, M. D. & Hart, S. R. Helium and neon isotopes in phenocrysts from Samoan lavas: evidence for heterogeneity in the terrestrial high 3 He/ 4 He mantle. Earth Planet. Sci. Lett. 287, 519–528 (2009).
Hoernle, K. et al. Existence of complex spatial zonation in the Galápagos plume. Geology 28, 435–438 (2000).
Adam, C., Vidal, V. & Escartín, J. 80-Myr history of buoyancy and volcanic fluxes along the trails of the Walvis and St. Helena hotspots (South Atlantic). Earth Planet. Sci. Lett. 261, 432–442 (2007).
Graham, D. W., Humphris, S. E., Jenkins, W. J. & Kurz, M. D. Helium isotope geochemistry of some volcanic rocks from Saint Helena. Earth Planet. Sci. Lett. 110, 121–131 (1992).
Merle, R. E., Jourdan, F., Chiaradia, M., Olierook, H. K. & Manatschal, G. Origin of widespread Cretaceous alkaline magmatism in the Central Atlantic: a single melting anomaly? Lithos 342, 480–498 (2019).
Geldmacher, J., Hoernle, K., van den Bogaard, P., Duggen, S. & Werner, R. New age and geochemical data from seamounts in the Canary and Madeira volcanic provinces: a contribution to the “Great Plume Debate”. AGU Fall Meeting 2004 abstr. V51B 0562 (AGU, 2004).
Moreira, M., Doucelance, R., Kurz, M. D., Dupré, B. & Allègre, C. J. Helium and lead isotope geochemistry of the Azores Archipelago. Earth Planet. Sci. Lett. 169, 189–205 (1999).
Doucelance, R., Escrig, S., Moreira, M., Gariepy, C. & Kurz, M. D. Pb–Sr–He isotope and trace element geochemistry of the Cape Verde Archipelago. Geochim. Cosmochim. Acta 67, 3717–3733 (2003).
Day, J. M. & Hilton, D. R. Origin of 3 He/ 4 He ratios in HIMU-type basalts constrained from Canary Island lavas. Earth Planet. Sci. Lett. 305, 226–234 (2011).
Clouard, V. & Bonneville, A. How many Pacific hotspots are fed by deep-mantle plumes? Geology 29, 695–698 (2001).
Castillo, P., Scarsi, P. & Craig, H. He, Sr, Nd, and Pb isotopic constraints on the origin of the Marquesas and other linear volcanic chains. Chem. Geol. 240, 205–221 (2007).
Hanyu, T. & Kaneoka, I. The uniform and low 3 He/ 4 He ratios of HIMU basalts as evidence for their origin as recycled materials. Nature 390, 273–276 (1997).
Garapić, G. et al. A radiogenic isotopic (He–Sr–Nd–Pb–Os) study of lavas from the Pitcairn hotspot: implications for the origin of EM-1 (enriched mantle 1). Lithos 228, 1–11 (2015).
Moreira, M. & Allègre, C. Helium isotopes on the Macdonald seamount (Austral chain): constraints on the origin of the superswell. C. R. Geosci. 336, 983–990 (2004).
2. Why are geophysical patterns interesting?
The Earth is not in thermodynamic equilibrium. Heat flows from the molten core to the crust, through a convecting mantle. Winds blow, rain falls and mountains erode, as the Sun's energy is processed and re-radiated to the cooler background of space. Life happens, and in doing so, changes the world. The means that shaped the geography that we see today are dynamic, complex, non-equilibrium and nonlinear. These are the natural conditions in which to expect self-organization, and the patterns that can be found tell us about the physics of these systems. Further, pattern-forming mechanisms can be very robust they are not only seen in controlled laboratory situations, but also survive (and can even thrive on) the noise of real-world geomorphic environments.
One strength of the modern approach to patterns is its universality. The same instability can appear in a great variety of situations. Turing's seminal paper on ‘The chemical basis of morphogenesis’, for example, outlined the conditions necessary for generating a linear instability in a system with two reacting, diffusing, chemical morphogens . In general, it applies to any two (or by a straightforward generalization, more) interacting fields u and v, where
This simple system is unstable to periodic stripes, or spots, when the ratio of diffusivities is sufficiently high, and the interaction terms f and g are alternatively excitatory (e.g. ∂f/∂uϠ) and inhibitory (∂g/∂vπ). Furthermore, the values of these terms, which can be derived from microscopic interactions, predict a most unstable length scale, at which patterns arise. This mechanism directly underlies about a third of the articles in this Theme Issue. L'Heureux  applies a form of it, close to its original intent, to show how periodic precipitation patterns are found in a variety of rocks. This banding is thus a permanent chemical record of the dynamical processes of its formation and can be read only with an appropriate understanding of the nonlinear feedbacks and instabilities of the system. The interacting variables can, however, be more subtle. Zelnik et al.  study the process of desertification in a series of models of dry-land vegetation, where moisture and biomass interact to give rise either to patterns of vegetative spots or bare soil. Penny et al.  share an observational study of a similar pattern, where symmetry is broken by hills, and the downslope drainage of the water leads to oriented stripes. Finally, Da Lio et al.  describe wetlands, where interactions between sediment flux and biomass stabilize a series of stepped vegetated platforms.
The universality of pattern-forming systems can also be a challenge. The patterned ground of permafrost soils has evident structure. Detailed numerical models can reproduce the shapes of this terrain well. However, as discussed by Hallet , such models can generate a similar pattern as the result of either frost heave or ground water convection. The frost-heave model is now preferred, but only as the result of cycles of prediction and validation. In another example, certain labyrinthine patterns in grasses look superficially like the reaction𠄽iffusion-based vegetation patterns of larger plants, but may result from the entirely different mechanism of porous-media convection . Similarity of form alone, no matter how beautiful, is insufficient for proof𠅊 useful model of pattern formation is necessarily quantitative, and describes additional features such as wavelength selection, scaling, rates or the location of bifurcation points between patterns in parameter space. In turn, these quantitative details guide further testing of models against field measurements and aid in the design of meaningful analogue experiments. Once an understanding is gained and tested, one can turn to interpretation, and here patterns can be powerful diagnostics of conditions that no longer exist or which (e.g. other planets, long time scales) are difficult to access directly.
The NAWI Graz Geocenter, and the master’s programme in Geosciences, combine basic research, applied research and engineering science in an integrated approach that is unique in the German-speaking countries. This programme is taught in English, reflecting its international perspective.
Is this degree programme right for you?
Interests that are a good basis for this study programme
You should have an interest in experimental and analytical laboratory activities, and enjoy both classic geological fieldwork, and computer-based modelling. A basic prerequisite for this master’s programme is a subject-relevant first degree.
About the study programme
Geosciences at the University of Graz
In this degree programme you will investigate the formation and structure of the Earth and life on it, and the safeguarding and use of natural resources. Research topics range from global processes (e.g. plate tectonics, oceanography, evolution) to geo- and hydrochemical processes on micro and nano levels, or the development of aquifers, to geotechnical applications. Für die Zulassung ist ein facheinschlägiges Vorstudium notwendig.
Doctoral Programme of Natural Sciences
The Doctoral Programme of Natural Sciences allows you to develop your own research interests further and to perfect your methodological skills. You will work independently to investigate academic questions and contribute to the development of knowledge and innovation in your subject area.
Preparation for a wide range of career paths
As a graduate of this master’s programme you will have a wide range of options for employment in academic and applied roles in the geosciences. Typical fields of work include the construction industry, water management, geotechnics, environmental and resource management, materials and chemical industries, geotechnics-oriented engineering consultancies, or museums and public authorities. You will also be able to work in basic and applied research in universities and non-university institutions.
Note on registration
Admission to the master’s programme is selective for anyone who is not a graduate of the subject-relevant bachelor’s programme at the University of Graz.
Get the exceptional preparation you need for a career as a geologist. In the SRU Geology program you won't just be sitting in the classroom, you'll be learning in the laboratory and field. You'll also have access to a number of exciting career development opportunities-including research, internships, and professional networking.
If you want a career that combines scientific inquiry with travel and the opportunity to work on real-world problems, the Geology program at Slippery Rock University is an excellent choice for you. There is a lot of demand for professional geologists across industries and SRU's program will give you the knowledge and skills you need to be one of them. Geology is a perfect fit if you have a strong interest in the physical history of the Earth and the changes it continues to undergo.