JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II FUNDAMENTALS OF GEOLOGY Previous Question Paper (March - 2021 - R15/R13)

The age of the Earth is determined using various geochronological methods, primarily based on the principles of radioactivity and the study of terrestrial and extraterrestrial materials. The most important methods include:

1. Radiometric Dating: This is the most accurate method, involving the measurement of the decay of long-lived radioactive isotopes. Key systems include Uranium-Lead (U-Pb), Rubidium-Strontium (Rb-Sr), and Potassium-Argon (K-Ar) dating.
2. Lead-Lead (Pb-Pb) Dating: By analyzing the ratios of lead isotopes in meteorites and Earth rocks, scientists can determine the time elapsed since the formation of the solar system, which is approximately 4.54 billion years.
3. Meteorite Analysis: Since Earth's original crust has been recycled through plate tectonics, scientists date chondritic meteorites, which are considered primordial remnants of the solar nebula that formed simultaneously with the Earth.
4. Zircon Dating: Zircon crystals are highly resistant to chemical weathering and metamorphism. Analyzing the oldest known zircon grains (such as those from the Jack Hills in Australia) provides a minimum age for the Earth's crust.

Volcanoes are classified based on their mode of eruption, frequency of activity, and physical structure. The primary classifications are:

1. Classification by Periodicity (Frequency of Eruption):
   • Active Volcanoes: Those that are currently erupting or have erupted in recent history (e.g., Mount Etna).
   • Dormant (Sleeping) Volcanoes: Those that are currently inactive but have the potential to erupt again (e.g., Mount Fuji).
   • Extinct (Dead) Volcanoes: Those that have not erupted in human history and show no signs of future activity due to the cessation of their magma supply.
2. Classification by Mode of Eruption:
   • Explosive Type: Characterized by highly viscous, gas-rich magma that causes violent eruptions (e.g., Plinian or Vulcanian eruptions).
   • Quiet Type: Characterized by low-viscosity, basaltic lava that flows easily, resulting in effusive eruptions (e.g., Hawaiian eruptions).
3. Classification by Structure:
   • Shield Volcanoes: Broad, gently sloping volcanoes formed by the accumulation of fluid basaltic lava flows.
   • Composite Volcanoes (Stratovolcanoes): Steep-sided, conical structures built from alternating layers of lava flows, volcanic ash, and pyroclastic debris.
   • Cinder Cones: Small, simple volcanoes built primarily from loose pyroclastic fragments ejected from a central vent.