(a) Compare the major morphological characters which differentiate Hominidae from ape-like primates. Discuss the evolutionary…

(a) Hominidae versus ape-like primates, and hominid evolution (20 marks)

Comparison. Here Hominidae means the human family, the bipedal hominins.

• Locomotion: hominins are habitually bipedal, with a foramen magnum placed forward under the skull, an S-shaped spine, a short broad pelvis, valgus knees and an arched foot with a non-opposable big toe. Apes are quadrupedal or knuckle-walkers, with a backward foramen magnum, a C-shaped spine, a long narrow pelvis and a grasping foot.
• Brain: about 400–500 cc in apes, rising from about 450 cc in Australopithecus to about 1350 cc in modern humans, with a high forehead.
• Teeth and jaw: hominins have small canines with no diastema, a parabolic dental arch and thick enamel; apes have large canines, a diastema and a U-shaped arch.
• Face and skull: the hominin face is flat (orthognathous) with a chin and reduced brow ridges; ape faces are prognathous, with a sagittal crest and no chin.
• Limbs and hand: hominin legs are longer than arms, and the hand has a precision grip. Apes have long arms.

Evolutionary trend. The sequence runs from Ardipithecus and Australopithecus through Homo habilis and Homo erectus to archaic and modern Homo sapiens, with increasing brain size, perfected bipedalism, reduction of face and teeth, and growing use of tools, fire and speech.

Indian evidence. The Siwalik Miocene–Pliocene beds (Haritalyangar, Ramnagar) yielded Sivapithecus (once called Ramapithecus), a ground-adapted ape, now regarded as related to the orangutan rather than as a hominin ancestor, and the giant ape Gigantopithecus. The hominin record in India begins with the Acheulian tools of Attirampakkam and the Narmada skull cap of Hathnora (an archaic Homo, about 0.2–0.5 million years old).

(b) Continental flood basalt, stratigraphy of the Deccan Trap and inter-trappean beds (15 marks)

Continental flood basalt (CFB). A CFB is a very large volume of basalt lava (up to millions of cubic kilometres), poured out from fissures onto the continent in a geologically short time, often about a million years, covering hundreds of thousands of square kilometres. The flows are mainly tholeiitic, low in viscosity, nearly horizontal and stacked, forming stepped "trap" plateaus, with columnar jointing, vesicular and amygdaloidal tops, red boles between flows, and dyke swarms as feeders. They are linked with mantle plumes and continental break-up. Examples are the Deccan Traps (66 Ma), Siberian Traps (252 Ma), Columbia River Basalts, Paraná–Etendeka, Karoo–Ferrar and Ethiopian Traps.

Stratigraphy of the Deccan Trap. The classical division is into Lower, Middle and Upper Traps. In the Western Ghats it is the Sahyadri Group, which is divided from bottom to top into three subgroups.

• Kalsubai: Jawhar, Igatpuri, Neral, Thakurvadi and Bhimashankar Formations.
• Lonavala: Khandala and Bushe Formations.
• Wai: Poladpur, Ambenali and Mahabaleshwar Formations.

Inter-trappean beds. These thin freshwater sedimentary beds (limestone, chert, shale, clay) formed in the pauses between eruptions. Their importance is that they contain fossils (plants, molluscs, ostracods, fish, frogs), which give the age (Late Cretaceous to Early Paleocene) and the humid palaeoenvironment, show the gaps between flows, and act as marker horizons and local aquifers.

(c) Hydrogeological properties of rock types and their role in groundwater studies (15 marks)

Properties. Porosity is the fraction of void space; permeability, measured as hydraulic conductivity K, is the ease of flow; specific yield Sy is the volume of water that drains by gravity per unit volume of aquifer; transmissivity T = Kb is the flow through the full thickness b; and storativity S is the water released per unit area per unit fall of head (S ≈ Sy in an unconfined aquifer, and 10⁻⁵–10⁻³ in a confined one).

Rock types.

• Unconsolidated sand and gravel: porosity 25–40%, high K, Sy 15–30%, excellent aquifers. Clay has high porosity but negligible K, so it is an aquitard.
• Sandstone: porosity 5–30%, moderate K and Sy 5–15%, a good aquifer, with fractures adding to flow.
• Shale: low porosity and K, so an aquiclude unless fractured.
• Limestone: low primary porosity, but solution channels and joints in karst give very high K and yields.
• Crystalline hard rock: primary porosity below 1%. Groundwater lies in the weathered layer and in fractures, Sy is 0.5–3%, and yields are small and variable.
• Basalt: groundwater lies in vesicular flow tops, joints, weathered layers and inter-trappean beds; yields are low to moderate.

Use. These properties allow aquifers to be identified and wells sited and designed, T and S to be found by pumping tests, flow to be computed from Darcy's law, recharge and resources to be estimated (Sy × area × water-table fluctuation), and recharge structures to be designed.