Our Home: Earth, a Unique Life Sustaining Planet

About this chapter

Our Home: Earth, a Unique Life Sustaining Planet is the final chapter of Class 8 Curiosity. It pulls together the year's learning to explain why Earth alone, among the eight planets of the Sun's solar system, can sustain life. Life exists on a thin layer — the crust — like the skin of an apple. Earth is in the Sun's habitable zone (Goldilocks zone), where the temperature lets water remain liquid. Venus is hotter than Mercury because its thick carbon-dioxide atmosphere traps heat — the greenhouse effect. Earth's near-circular orbit, just-right size and gravity hold a life-supporting atmosphere; ozone blocks ultraviolet rays and the magnetic field shields against cosmic rays and solar wind. Life is sustained by air, water and sunlight; soil, rocks and minerals make the geosphere; living beings together form the biosphere; water bodies form the hydrosphere; and geodiversity supports many habitats. Reproduction — asexual (binary fission, budding, vegetative propagation) and sexual (gametes, pollination, fertilisation, zygote) — keeps life continuing. The chapter ends with the triple planetary crisis — climate change, biodiversity loss, pollution — and global agreements (Montreal 1987, Earth Summit 1992, Kyoto 2005, Paris 2015). CTET Paper 2 Science tests definitions, the Goldilocks idea, atmosphere-gravity logic, asexual-sexual contrast and pollution-cause reasoning. The four tests — Practice 15, Quiz 15, Hard 15, Mastery 30 — cover these.