The upper portion of the Earth is known as:
- (a)Lithosphere
- (b)Mesosphere
- (c)Troposphere
- (d)Stratosphere
Answer
Why
Correct — A. The question asks for the upper portion of the solid Earth, and that outermost rigid shell is the lithosphere — the crust together with the rigid top of the mantle.
It is the layer you stand on, and it is broken into the tectonic plates that carry the continents. Below it lies the softer, slowly deforming asthenosphere.
Read against this option set, the other three name layers of the atmosphere — troposphere, stratosphere, mesosphere, in that order upward. Option (a) is the only one that answers a question about rock.
Why the others are wrong
- (b)Mesosphere — The mesosphere is the atmospheric layer above the stratosphere, where most meteors burn up. It is a layer of air, not the Earth's solid outer shell.
- (c)Troposphere — The troposphere is the lowest layer of the atmosphere and holds almost all weather and water vapour. It sits above the lithosphere rather than being it.
- (d)Stratosphere — The stratosphere lies above the troposphere and carries the ozone layer. Like the other rejected names it describes air, not the Earth's outermost rock.
Concept
The solid Earth is layered by composition into crust, mantle and core. A second scheme layers the same rock by how it behaves: the rigid lithosphere on top, then the weak, slowly flowing asthenosphere beneath it.
So the lithosphere is not a synonym for the crust. It is the crust plus the uppermost rigid mantle, and its fragmentation into plates is what makes plate tectonics possible.
The atmosphere has its own family of "-sphere" names, and SSC leans on that collision of vocabulary.
The stem's wording, upper portion of the Earth, is loose — it means the outermost solid shell, not the outermost layer of air.
Read the options before the stem here: three of them name atmospheric layers and one names a layer of rock.
One caveat on mesosphere. The word does double duty — in the older rheological scheme for the Earth's interior it is a name for the lower mantle, so it is not purely an air word.
That sense does not rescue option (b) either: the lower mantle is the deep interior, and the stem asks for the upper portion.
Key facts
- The lithosphere is the crust plus the rigid uppermost part of the mantle.
- The asthenosphere lies directly below the lithosphere and deforms plastically.
- Troposphere, stratosphere and mesosphere are layers of the atmosphere, in that order upward.
- The lithosphere is broken into the tectonic plates.
Study next
Common traps
- Treating lithosphere and crust as the same thing, when the lithosphere also includes the rigid top of the mantle.
- Picking an atmospheric layer because the stem says upper — the question is about the Earth's body, not its air.
SSC tests Earth structure by naming a position and asking for the layer. The same blank with a different adjective ran at 18 Sep 2024, 9:00, GA Q.5 — the outermost part of the Earth, keyed the crust against core, mantle and volcano.
One stem says outermost and keys crust, this one says upper portion and keys lithosphere. Read the option set before you answer, because it decides which of the two schemes is in play.
Related PYQs
No directly related past PYQ was found.