Question

how does temperature and pressure varie in earths layer

Answer 1

Short answer: both temperature and pressure increase with depth in Earth, but they do so at different rates in different layers. Pressure rises roughly steadily because of the weight of overlying rock; temperature rises too but the temperature gradient changes (steep in the crust, much gentler through most of the mantle). Those differences control whether material is solid or liquid at a given depth.

Typical approximate values by layer (depths, pressure and temperature are approximate and vary regionally):

- Surface (0 km)
- Pressure: ~0 GPa
- Temperature: ~–10 to +30 °C (surface climate-dependent)

- Crust (oceanic ~0–10 km; continental ~0–35 km, can be 70+ km under some mountains)
- Pressure: ~0 → 1 GPa (≈0–30 MPa/km × depth; ~1 GPa at ~35 km)
- Temperature: ~surface → ~200–600 °C at the base of the crust (geothermal gradient typically ~10–30 °C/km; oceanic crust tends to be hotter at shallow depths because it is thinner)

- Upper mantle / lithosphere-asthenosphere (~35–100/200 km)
- Pressure: ~1 → 3–6 GPa
- Temperature: ~400 → ~1300 °C (the base of the lithosphere is often near the peridotite solidus ≈1200–1400 °C)

- Transition zone (≈410–660 km)
- Pressure: ~13 → ~24 GPa
- Temperature: roughly ~1400 → ~2000 °C (minerals undergo phase changes here)

- Lower mantle (≈660–2900 km)
- Pressure: ~24 → ~136 GPa (pressure rises strongly because density increases with depth)
- Temperature: roughly ~2000 → ~2500–4000 °C (gradual, near-adiabatic temperature increase)

- Core–mantle boundary (≈2900 km)
- Pressure: ~130–140 GPa
- Temperature: ~2500–4000 °C (estimates vary)

- Outer core (≈2900–5150 km)
- Pressure: ~140 → ~330 GPa
- Temperature: ~3500 → ~5000+ °C
- State: liquid (mainly iron–nickel alloy)

- Inner core (≈5150–6371 km, center)
- Pressure: ~330 → ~360 GPa (central pressure ≈330–360 GPa)
- Temperature: ~5000 → ~6000+ °C (estimates often ~5000–6000 °C)
- State: solid iron–nickel

Why the differences matter
- Pressure increases because of the weight of overlying material (roughly 30 MPa per km near the surface on average, but increasing density with depth changes the rate).
- Temperature increases from primordial heat, radioactive decay, and adiabatic compression. The geothermal gradient is steep in the upper crust (so temperature rises quickly with depth there) but becomes much gentler through most of the mantle (an approximately adiabatic profile).
- Whether rock is solid or molten depends on both temperature and pressure: for example the outer core is molten because temperatures exceed the melting point at those pressures, while the inner core is solid because the much higher pressure raises the melting point enough to solidify iron despite higher temperature.

How we know these numbers
- Direct measurements in boreholes only reach a few km. Deeper values come from seismic wave studies (which give densities and phase boundaries), high-pressure laboratory experiments on minerals, and modeling of heat flow and planetary composition.

If you want, I can:
- show a simple depth vs temperature/pressure plot,
- give a more precise table with values from a standard Earth model (e.g., PREM), or
- explain in more detail how seismic data and mineral physics are used to estimate deep temperatures and pressures.