UPCAT General Science (Extended) — Universe, Solar System & EarthRevision Notes
Condensed revision notes for Universe, Solar System & Earth, built for the final weeks before the UPCAT 2026. These are the distilled key points you need when there is no time left for full study notes — just the concepts, formulas, and traps University of the Philippines tests.
Exam context
The University of the Philippines College Admission Test is conducted by University of the Philippines and is scheduled for Mid-2026 (announced by UP Admissions). The General Science (Extended) subtest is marked as "Extended coverage for UP Science programs" in the official pattern, and Universe, Solar System & Earth appears in position 3rd of 6 in the UPCAT General Science (Extended) review rotation. Passing mark: UPG ≤ 2.2 typical. Recent UPCAT 2026 papers have drawn roughly 20 questions from this subject.
Universe, Solar System & Earth - Revision notes
This chapter explores the origin and structure of the universe, the formation and characteristics of our solar system, and the unique features that make Earth habitable. Understanding these concepts is crucial for UPCAT and other college entrance exams as they form the foundation of Earth Science and Astronomy. We'll examine the Big Bang Theory, planetary formation, Earth's internal structure, geological processes, and the interconnected systems that sustain life on our planet.
Sections
Formulas
Example
The formation of first stars occurred about 200 million years after the Big Bang
Formula
Age of Universe ≈ 13.8 billion years
Variables
Based on cosmic microwave background measurements
Application
Determining timeline of cosmic events
Exam Tips
- Memorize the major epochs and their temperatures in chronological order
- Understand that the Big Bang created space, time, matter, and energy simultaneously
- Know the current composition percentages of the universe
Key Points
- The Big Bang Theory explains that the universe began from a singularity 13.8 billion years ago
- The universe started as an infinitely hot, dense point and expanded rapidly
- The Radiation Era (first stage) was dominated by high-energy particles and radiation
- Key epochs in Radiation Era: Planck (10^40 K), Grand Unification, Inflationary, Electroweak, Quark, Hadron, Lepton, and Nuclear
- The Matter Era began when matter became dominant, leading to atom formation and galaxy development
- Universe composition: 4.6% ordinary matter, 24% dark matter, 71.4% dark energy
- Evidence includes cosmic microwave background radiation and redshift of distant galaxies
Definitions
Term
Singularity
Definition
An infinitely hot and dense point from which the universe originated
Importance
Represents the initial condition before the Big Bang expansion
Term
Recombination
Definition
The epoch when electrons combined with nuclei to form neutral atoms
Importance
Allowed light to travel freely, making the universe transparent
Term
Dark Matter
Definition
Matter that doesn't emit light but has gravitational effects
Importance
Makes up 24% of the universe and affects galaxy formation
Section Title
Formation of the Universe: Big Bang Theory
Common Mistakes
- Confusing the Big Bang as an explosion in space rather than an expansion of space itself
- Mixing up the order of epochs in the Radiation Era
- Thinking the universe has a center or edge
Formulas
Example
Jupiter is approximately 5.2 AU from the Sun
Formula
1 AU = 150 million km
Variables
AU = Astronomical Unit (Sun-Earth distance)
Application
Measuring distances within the solar system
Exam Tips
- Use mnemonics like 'My Very Educated Mother Just Served Us Nachos' for planet order
- Remember that density decreases as you move outward from the Sun (generally)
- Know the age of the solar system (4.568 billion years)
Key Points
- Solar system formed approximately 4.568 billion years ago from a stellar explosion
- Nebular hypothesis explains formation from a rotating disk of gas and dust
- Inner terrestrial planets formed from heavier materials near the Sun
- Outer gas giants formed from lighter materials in cooler regions
- Solar winds pushed lighter elements outward during formation
- Asteroid belt between Mars and Jupiter contains remnants of failed planet formation
- Kuiper belt (beyond Neptune) and Oort cloud mark outer boundaries
Definitions
Term
Terrestrial Planets
Definition
Rocky planets with solid surfaces (Mercury, Venus, Earth, Mars)
Importance
Located in inner solar system, made of silicates and metals
Term
Gas Giants
Definition
Large planets composed mainly of hydrogen and helium (Jupiter, Saturn, Uranus, Neptune)
Importance
Located in outer solar system, have thick atmospheres and many moons
Term
Goldilocks Zone
Definition
The habitable zone where liquid water can exist on a planet's surface
Importance
Earth's position in this zone allows for liquid water and life
Section Title
Formation of the Solar System
Common Mistakes
- Confusing the order of planets from the Sun
- Mixing up characteristics of terrestrial vs gas giant planets
- Forgetting that Pluto is now classified as a dwarf planet
Formulas
Example
The core's high density explains why it contains iron and nickel
Formula
Density increases with depth: Crust (2.7 g/cm³) < Mantle (4.5 g/cm³) < Core (10-13 g/cm³)
Variables
g/cm³ = grams per cubic centimeter
Application
Understanding Earth's layered structure
Exam Tips
- Remember the two classification systems: compositional (core, mantle, crust) and structural (lithosphere, asthenosphere, etc.)
- Know that temperature and pressure increase with depth
- Understand that the magnetic field is generated by the liquid outer core
Key Points
- Earth formed through accretion of dust and debris about 4.568 billion years ago
- Differentiation created layers: core (iron/nickel), mantle (silicates), crust (lightest materials)
- Moon formed from debris after collision with planet-sized object called Theia
- Earth's magnetic field generated by liquid outer core protects from solar radiation
- Atmosphere developed through outgassing and later modified by life processes
- Water likely delivered by comets and contained in original materials
Definitions
Term
Differentiation
Definition
Process where materials separate based on density, with heavier materials sinking toward the center
Importance
Explains Earth's layered structure and core composition
Term
Lithosphere
Definition
Rigid outer layer including crust and upper mantle
Importance
Forms tectonic plates that move and cause geological activity
Term
Asthenosphere
Definition
Semi-fluid layer in upper mantle beneath lithosphere
Importance
Allows tectonic plates to move and provides material for volcanism
Section Title
Formation and Structure of Earth
Common Mistakes
- Confusing the inner core (solid) with outer core (liquid)
- Mixing up compositional vs structural layers of Earth
- Thinking the mantle is liquid throughout
Exam Tips
- Know Wegener's four main pieces of evidence by heart
- Understand that plate tectonics explains the 'how' that continental drift couldn't
- Remember that earthquakes occur at all three types of plate boundaries
Key Points
- Alfred Wegener proposed Continental Drift Theory in 1915
- Evidence includes continental fit, fossil correlation, rock correlation, and paleoclimate data
- Pangaea was the supercontinent that existed 250 million years ago
- Seafloor spreading explains mechanism of continental movement
- Plate tectonics theory explains earthquakes, volcanoes, and mountain formation
- Three types of plate boundaries: divergent, convergent, and transform
- Convection in mantle drives plate movement
Definitions
Term
Continental Drift
Definition
Theory that continents move slowly across Earth's surface over geological time
Importance
Explains distribution of fossils, rocks, and ancient climates
Term
Seafloor Spreading
Definition
Process where new oceanic crust forms at mid-ocean ridges and spreads outward
Importance
Provides mechanism for continental drift and explains ocean floor age patterns
Term
Subduction
Definition
Process where oceanic plate descends beneath another plate into the mantle
Importance
Recycles oceanic crust and creates deep ocean trenches and volcanic activity
Section Title
Continental Drift and Plate Tectonics
Common Mistakes
- Confusing the evidence types for continental drift
- Not understanding the difference between divergent and convergent boundaries
- Forgetting that oceanic crust is denser than continental crust
Formulas
Example
If P-waves arrive 3 minutes before S-waves, the earthquake is approximately 1,800 km away
Formula
P-wave velocity > S-wave velocity
Variables
P-waves arrive first at seismic stations
Application
Determining earthquake epicenter location using time difference
Exam Tips
- Remember: P-waves are Primary (first), S-waves are Secondary (second)
- Know that S-waves cannot travel through liquids (important for studying Earth's core)
- Understand the relationship between wave types and damage potential
Key Points
- Earthquakes result from sudden energy release along faults
- Focus (hypocenter) is the underground origin point; epicenter is directly above on surface
- Four types of seismic waves: P-waves, S-waves, Love waves, and Rayleigh waves
- P-waves are fastest and can travel through solids and liquids
- S-waves are slower and only travel through solids
- Surface waves (Love and Rayleigh) cause most earthquake damage
- Richter scale measures earthquake magnitude from 1-9
Definitions
Term
Focus (Hypocenter)
Definition
The actual location underground where an earthquake begins
Importance
Determines the depth and intensity distribution of earthquake effects
Term
Epicenter
Definition
The point on Earth's surface directly above the focus
Importance
Usually experiences the strongest shaking and most damage
Term
Seismograph
Definition
Instrument that detects and records seismic waves
Importance
Allows scientists to locate earthquake epicenters and study Earth's interior
Section Title
Earthquakes and Seismic Waves
Common Mistakes
- Confusing focus and epicenter locations
- Thinking S-waves travel faster than P-waves
- Not understanding that surface waves cause the most damage
Exam Tips
- Know examples of each rock type and their formation processes
- Understand that the rock cycle is continuous and multi-directional
- Remember key processes: crystallization, weathering, lithification, metamorphism
Key Points
- Three main rock types: igneous, sedimentary, and metamorphic
- Rock cycle shows transformation between rock types
- Igneous rocks form from cooling magma/lava (intrusive vs extrusive)
- Sedimentary rocks form from weathering, erosion, deposition, and lithification
- Metamorphic rocks form from heat and pressure on existing rocks
- Key processes: weathering, erosion, deposition, compaction, metamorphism
- Any rock type can transform into any other rock type
Definitions
Term
Weathering
Definition
Physical, chemical, or biological breakdown of rocks at Earth's surface
Importance
First step in sedimentary rock formation and soil development
Term
Lithification
Definition
Process of converting loose sediments into solid sedimentary rock
Importance
Involves compaction and cementation of sediments
Term
Metamorphism
Definition
Transformation of existing rocks due to heat, pressure, and chemical reactions
Importance
Creates new minerals and rock textures without melting
Section Title
Rock Cycle and Rock Types
Common Mistakes
- Thinking rocks can only transform in one direction
- Confusing intrusive and extrusive igneous rocks
- Not understanding that metamorphic rocks don't melt during formation
Formulas
Example
Increase in CO₂ from 0.03% to 0.04% has significant climate effects
Formula
Atmospheric composition: N₂ (78%) + O₂ (21%) + Ar (0.93%) + CO₂ (0.04%) + trace gases
Variables
Percentages by volume at sea level
Application
Understanding atmospheric composition for climate and life processes
Exam Tips
- Know the characteristics of each atmospheric layer
- Understand examples of sphere interactions (like water cycle involving all four spheres)
- Remember the three Philippine UNESCO Biosphere Reserves
Key Points
- Four main Earth spheres: lithosphere, atmosphere, hydrosphere, biosphere
- Atmosphere has five layers: troposphere, stratosphere, mesosphere, thermosphere, exosphere
- Hydrosphere includes all water in liquid, solid, and gas phases (97% saltwater, 3% freshwater)
- Biosphere contains all living organisms and has existed for 3.8 billion years
- Greenhouse effect keeps Earth warm enough for life
- Water cycle connects all spheres and distributes heat and moisture
- Human activities affect all Earth systems, especially through greenhouse gas emissions
Definitions
Term
Greenhouse Effect
Definition
Process where atmospheric gases trap heat from the sun, warming Earth's surface
Importance
Natural process essential for life; enhanced by human activities
Term
Hydrologic Cycle
Definition
Continuous movement of water through evaporation, condensation, precipitation, and collection
Importance
Distributes heat and moisture globally, shapes landscapes
Term
Biosphere Reserve
Definition
Protected area that conserves biodiversity while allowing sustainable human activities
Importance
Philippines has three UNESCO Biosphere Reserves: Albay, Palawan, Puerto Galera
Section Title
Earth's Spheres and Interactions
Common Mistakes
- Confusing the order of atmospheric layers
- Not understanding how the spheres interact with each other
- Thinking greenhouse effect is entirely bad (it's natural and necessary)
Connections
- Universe formation connects to stellar evolution and element formation in stars
- Plate tectonics relates to earthquake distribution and volcanic activity patterns
- Rock cycle demonstrates matter conservation and energy transformation principles
- Earth's spheres show system interactions similar to ecosystem relationships in biology
- Greenhouse effect connects to climate change and environmental chemistry
- Seismic waves relate to wave properties studied in physics
- Planetary formation connects to gravitational principles and orbital mechanics
Exam Strategy
Focus on understanding processes rather than just memorizing facts. Practice identifying cause-and-effect relationships, especially in geological processes. Know the evidence for major theories (Big Bang, Continental Drift, Plate Tectonics). Memorize key numbers (ages, compositions, measurements) as they frequently appear in multiple choice questions. Draw diagrams to visualize Earth's layers, plate boundaries, and sphere interactions. Connect concepts across topics - for example, how plate tectonics explains earthquake distribution and volcanic activity. Pay special attention to Philippine examples like the three UNESCO Biosphere Reserves.
Quick Review Questions
What evidence supports the Big Bang Theory?
These observations confirm the universe is expanding and was once much hotter and denser
What are Wegener's four pieces of evidence for Continental Drift?
These show that continents were once connected and have moved over geological time
Which seismic waves arrive first and can travel through liquids?
P-waves are compressional waves that travel fastest and can move through both solids and liquids
What makes Earth habitable compared to other planets?
These factors combine to create conditions suitable for liquid water and life as we know it
What drives plate tectonic movement?
Hot material rises and cool material sinks, creating circulation patterns that move tectonic plates
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