(a) Define species and explain how paleontological species are different from biological species. (10 marks) (b) Discuss the…

(a) Species and paleospecies. A species is a basic unit of biological classification; in Mayr's biological species concept, it is a group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. This definition depends on living organisms, gene flow, and observable reproductive barriers. Paleontological species are inferred from fossils, where interbreeding cannot be tested directly. They are therefore usually defined as morphospecies, based on consistent anatomical, shell, tooth, or skeletal differences, and as chronospecies when a lineage changes through time. The temporal dimension is central: a paleospecies is a name given to a fossil form within a defined stratigraphic interval, and its boundaries may be revised as new fossils appear. This distinction is important in fossil records where only hard parts are preserved. Palaeontologists must also allow for ontogenetic growth, sexual dimorphism and ecophenotypic variation, and they use stratigraphic position as an additional criterion; a fossil population from one horizon and locality is called a palaeodeme. Thus, biological species stress reproductive isolation among living populations, while paleontological species stress morphology, ancestry, and time, with less certainty about gene flow.

(b) Dharwar subcratons. The Dharwar Craton is subdivided into Western and Eastern Dharwar Craton using structural, lithological, and geochronological parameters. The Western Dharwar Craton is dominated by older 3.0–3.4 Ga tonalite–trondhjemite–granodiorite gneisses, with associated greenstone belts that are largely NNW–SSE trending (older Sargur-type belts, ~3.3–3.0 Ga). It represents an older crustal block with thick volcano-sedimentary greenstone successions. The Eastern Dharwar Craton is characterised by younger 2.5–2.7 Ga juvenile crust, with N–S trending structures, younger Kolar–Hutti-type greenstone belts (~2.7–2.55 Ga) and a different lithological assemblage. The Kolar schist belt lies in this eastern part and records later deformation and metamorphism. The contrast in age, trend, and rock type shows that the two subcratons are not merely regional variations but distinct crustal domains separated by a major structural boundary. In practice, the boundary is traced along the Chitradurga shear zone, and where zircon ages shift from older TTG to younger granitoid ages. Other parameters support the division: the western greenstone belts (Bababudan, Chitradurga) are sediment-rich, while the eastern belts (Kolar, Hutti, Ramagiri) are dominantly volcanic; the western crust is thicker (about 40–45 km against 33–38 km) and preserves older Nd model ages. Some recent studies recognise a third, central block between the two. The boundary is commonly marked by the ~2.5 Ga Closepet granite and the Chitradurga shear zone; the Eastern Ghats Mobile Belt lies to the east of the craton and is not the WDC–EDC divide.

(c) Cretaceous volcanic province. The Cretaceous volcanic province in India is the Deccan Traps, a large flood-basalt province developed near the Cretaceous–Paleogene (K–Pg) boundary, about 66 Ma (current estimates span about 67–64 Ma). It covers large parts of Maharashtra, Gujarat, Madhya Pradesh, Karnataka and Telangana and is petrologically dominated by tholeiitic basalts. The stratigraphy is commonly divided into three subgroups: the Lower Kalsubai subgroup, the Middle Lonavala subgroup, and the Upper Wai subgroup. These subgroups show variations in lava thickness, flow type, and minor volcanic units, but together form a thick sequence of stacked basalt flows. The three subgroups are described from their vertical succession and lithological changes. The province is distinct from the older (~118–115 Ma) Rajmahal and Sylhet traps, which are Kerguelen-plume basalts, whereas the Deccan is linked to the Réunion plume and to India–Seychelles rifting at ~62.5 Ma. The province covers about 500,000 km² today (original extent up to ~1.5 million km²), exceeds 2 km in thickness in the Western Ghats and has a volume of the order of 5 × 10^5 km³; intertrappean beds between flows carry freshwater fossils. Other Cretaceous volcanic units in India are the Early Cretaceous Rajmahal–Sylhet traps and the ~90 Ma rhyolites of St. Mary's Islands (Karnataka), linked to the Marion hotspot and India–Madagascar separation. The Deccan Traps are therefore described as a major Cretaceous–Paleogene volcanic province with broad areal extent, tholeiitic composition, and a threefold stratigraphic subdivision.

(d) Darcy's law and Reynolds' number. Darcy's law describes laminar flow of water through porous media. It is written as v = -(kρg/μ) × dh/dl, where v is flow velocity, k is intrinsic permeability, ρg is the unit weight of water, μ is fluid viscosity, and dh/dl is the hydraulic gradient. The negative sign shows that flow is from higher to lower hydraulic head. In aquifers, Darcy's law is useful because groundwater usually moves slowly through pore spaces, so the flow is laminar and proportional to the head difference. Reynolds' number, Re = ρvd/μ, is used to test whether that assumption is valid. It compares inertial forces to viscous forces, using fluid density ρ, characteristic velocity v, particle or pore diameter d, and viscosity μ. In groundwater flow, laminar conditions are generally maintained when Re is below the critical range of about 1–10. Above this range, flow may become transitional or turbulent, and Darcy's linear relation may no longer describe the aquifer accurately; non-linear (Forchheimer) laws then apply, as in gravels, karst conduits and near pumping wells. The Darcy velocity is a specific discharge q. By convention, Reynolds number in groundwater uses q and a representative grain diameter, while the average linear velocity (q/n_e, where n_e is the effective porosity) is used to estimate travel times.

(e) Landslide rehabilitation. Rehabilitation of a landslide-affected area is described in stages that restore both the community and the ecology. Structural measures are used first to stabilise the slope: retaining walls, check dams, drainage channels, slope grading, and anchoring reduce pore pressure and prevent further movement. Bioengineering measures are then applied to bind the soil and rebuild vegetation, using vetiver grass, shrubs, and native afforestation suited to the local slope and rainfall. Prevention also requires landslide susceptibility zonation and hazard mapping (following GSI and NDMA guidelines) and land-use regulation that keeps construction off steep slopes and drainage lines. In Western Ghats or Himalayan cases, these measures are combined with terracing, plantation of native species, and protection of residual soil. Community restoration includes safe resettlement, access roads, water supply, livelihood support, and early warning systems so that people can return or relocate safely. After the July 2024 Wayanad landslides (Mundakkai–Chooralmala), for example, Kerala planned model townships for resettlement away from the debris-flow path. Ecological restoration is completed by re-establishing native plant cover, protecting water sources, and monitoring slope stability and vegetation recovery over time. Rehabilitation therefore proceeds stage-wise: emergency stabilisation → slope treatment → community restoration → ecological recovery, with monitoring (piezometers, inclinometers) to verify stability.