Earth as a Planet Overview

Study Notes

The Earth is a rocky planet, one astronomical unit from the Sun.
Its diameter is 13,000 km.
It has five main layers.
The outer layer is a thin atmosphere/ocean.
The breathable part of the atmosphere is only 3-5 km.
The ocean's maximum depth is about 8km.
Rocky layers are either liquid or solid, depending on pressure, temperature, and elements present.
Pressure increases with depth, increasing melting points.
Temperature increases with depth.
Temperature must be higher than pressure-related melting point for a layer to melt.
Silicate rock melts at a lower temperature than iron rich material.
The outer layer is the crust.
Land crust is approximately 80 km thick, thinner under oceans at about 8 km.
The crust is mainly composed of silicate rock rich in lighter elements (calcium, magnesium, aluminium).
The mantle lies beneath the crust and is approximately 2800 km thick.
It is solid near the bottom, and behaves like a liquid in lower pressure areas.
The bottom of the crust and top of the mantle are linked by the Mohorovicic discontinuity (Moho).
It is marked by a change in chemical composition.
The mantle is partially melted in nature.
Heat rises in the mantle via convection plumes, pushing tectonic plates.
Heat plumes cause volcanoes.
The outer core is mainly iron and liquid.
The inner core is pure iron under immense pressure, not melting despite the high temperature.
Approximately 5,000°C.

Stars are extremely distant from Earth.
Apparent angle to stars changes very little.
Measuring the Moon's orbit against fixed stars gives a 27.3-day period (sidereal period).
Measuring the Moon's orbit against Earth-Sun positions gives a 29.5-day period (synodic period).
This difference is due to the Earth's movement.
The Earth orbits the Sun in 365.25 days (sidereal).
Orbit movement is approximately 1 degree per day.
The Sun appears to move westwards from daily perspective due to Earth's rotation.
Culmination is the Sun at its highest point(local noon).
The Earth must rotate an extra degree to account for the Sun's movement, taking ~4 minutes.
A sidereal day is 23 hours and 56 minutes.
A synodic day is exactly 24 hours.

The Moon formed from ejected material from a collision between Earth and a Mars-sized body (Theia).
Evidence includes dehydrated lunar soil (regolith), imbalances in isotopes, and kreep-rich rocks.
The Moon's visible surface shows a contrast between dark, flat seas (maria) and lighter, rough highlands.
Highlands are primarily overlapping craters, formed from high-speed impacts.
The craters are mostly circular due to shockwave travel from impact.
Craters are categorized by size (simple, complex, basins).
Larger craters have terraced walls, flat bottoms (basins) and central peaks.
Impact basins are huge and fill with molten lava, creating flat maria.
Some additional features include rilles (linear features), wrinkle ridges, and mountain ranges.
These features are associated with past cratering and cooling.
Apollo missions have mapped the lunar surface.
Some specific sites (e.g., Sea of Tranquility, Ocean of Storms, Tycho) are notable.