#Planetary differentiation
How rocky worlds separate into core, mantle and crust, and the meteorites that sample each layer.
When a young asteroid or planet grows large and hot enough, it melts and separates into layers. Dense metal sinks to form a core, and lighter rock floats up to form a mantle and a crust. Earth went through the same process, but its core is far out of reach.
Meteorites give us samples of every layer from small worlds that later broke apart. Iron meteorites are pieces of metal cores. The HED meteorites are crust and deeper rock from the asteroid Vesta. Pallasites, with green olivine crystals set in metal, are thought to come from where metal and rock met.
Studying these rocks shows how quickly the first planets melted and layered, and helps explain how Earth built its own core, mantle and crust.
Part of Meteorites across the sciences.
Lessons (6)
- Achondrites: rocks from melted worldsAchondrites are stony meteorites without chondrules. They come from worlds that melted, and many of them look surprisingly like volcanic roc
- Iron meteorites: cores, cooling and dynamosIron meteorites preserve quantitative records of how asteroid cores crystallised and cooled, and even whether they generated magnetic fields
- Iron meteorites and their hidden patternsIron meteorites are pieces of the metal cores of shattered asteroids. Cut one open and etch it, and many reveal a beautiful crystal pattern
- Primitive achondrites and ureilitesBetween chondrites and fully melted achondrites lie rocks caught in the act of melting. They reveal how differentiation begins.
- Stony-irons: pallasites and mesosideritesStony-iron meteorites are rare mixtures of metal and rock. They include some of the most beautiful objects that fall from the sky.
- The classification frameworkMeteorite classification is a hierarchy built on petrology, bulk chemistry and isotopes.
Courses (4)
- Extinct radionuclides and the first few million yearsSome radioactive isotopes present when the Solar System formed have long since decayed away.
- The metallurgy of iron meteoritesIron meteorites are pieces of asteroid cores that cooled over millions of years. Their crystal structures and nickel distributions record co
- Worlds that meltedSome early asteroids melted and separated into core, mantle and crust, then were shattered.
- Inside a planet: cores, mantles and crustsNobody can drill to Earth's core, but meteorites let us hold pieces of the cores, mantles and crusts of other worlds.
Famous meteorites (2)
Meteorite types (9)
- AchondritesIgneous stones from bodies that melted: asteroids, the Moon and Mars. An achondrite is a stony meteorite without chondrules.
- Asteroidal achondritesFully melted, differentiated rocks from the crusts and mantles of asteroids, Vesta above all.
- AubritesPale, almost iron-free rocks made of enstatite, from an extremely oxygen-poor world.
- DiogenitesPyroxene-rich rocks from deep inside Vesta. Diogenites are coarse-grained rocks made mostly of orthopyroxene, sometimes with olivine.
- Eagle Station pallasitesA tiny grouplet of pallasites with iron-rich olivine and nickel-rich metal, from a separate parent body.
- HED meteorites: pieces of VestaThe howardites, eucrites and diogenites: crust and mantle rocks from the giant asteroid 4 Vesta. The meteorites this site is named after.
- Main-group pallasitesNine in ten pallasites: magnesium-rich olivine in metal related to the IIIAB irons.
- PallasitesGem-like olivine crystals set in iron-nickel metal. Pallasites contain large olive-green crystals of olivine embedded in iron-nickel metal.
- ShergottitesThe most common Martian meteorites: young basaltic and olivine-rich rocks. Shergottites, named after Shergotty in India (fell 1865), make up
Meteorite minerals (1)
- RingwooditeThe dense, spinel-structured form of olivine, made by shock in meteorites and found deep inside Earth.
Glossary (6)
Questions and answers (10)
- Can meteorites tell us what is inside Earth?Yes. Iron meteorites are samples of planetary cores, and chondrites show the raw materials Earth was built from, helping scientists estimate
- How can I teach the origin of the Solar System using meteorites?Meteorites record the sequence from dust and the first solids to planetesimals, melting and differentiation, so pupils can build a timeline
- How can I use meteorites to teach Earth's layers?Iron meteorites model Earth's metal core, pallasites the core-mantle region and stony meteorites the mantle and crust, helping pupils un
- How can meteorites be used in A-level geology?Meteorites illustrate igneous and metamorphic petrology, crystallisation, isotope geochemistry and planetary differentiation, and thin secti
- How do I differentiate meteorite lessons for different abilities?Offer the same core activity with different levels of support and challenge: word banks and picture cards for some, calculations and open in
- What are primitive achondrites?Primitive achondrites are meteorites that were heated enough to partly melt but kept much of their original chondritic chemistry, such as ac
- What is a pallasite and how did it form?A pallasite is a stony-iron meteorite of olivine crystals in iron-nickel metal. Most likely formed where core metal and mantle olivine mixed
- What is a stony-iron meteorite?A stony-iron meteorite is made of roughly equal amounts of iron-nickel metal and silicate rock. The two main kinds are pallasites and mesosi
- What is Vesta?Vesta is the second-largest body in the asteroid belt, about 525 kilometres across.
- Why do iron meteorites come from so many parent bodies?Iron meteorites come from the cores of many small planetesimals that melted early; their strength lets them survive while the rocky outer la
Meteorites (the 60 largest of 2,540)
- HobaIron, IVB · Namibia
- Cape YorkIron, IIIAB · Not recorded
- Campo del CieloIron, IAB-MG · Argentina
- Canyon DiabloIron, IAB-MG · United States
- ArmantyIron, IIIE · China
- GibeonIron, IVA · Namibia
- ChupaderosIron, IIIAB · Mexico
- MundrabillaIron, IAB-ung · Australia
- Sikhote-AlinIron, IIAB · Russia
- BacubiritoIron, ungrouped · Mexico
- MbosiIron, ungrouped · Tanzania
- WillametteIron, IIIAB · United States
- MoritoIron, IIIAB · Mexico
- NantanIron, IAB-MG · China
- CranbourneIron, IAB-MG · Australia
- Santa CatharinaIron, IAB-ung · Brazil
- BendegóIron, IC · Brazil
- BrenhamPallasite, PMG-an · United States
- Vaca MuertaMesosiderite-A1 · Chile
- YoundeginIron, IAB-MG · Australia
- XifuIron, IAB complex · China
- YingdeIron, IVA · China
- TolucaIron, IAB-sLL · Mexico
- Old WomanIron, IIAB · United States
- WabarIron, IIIAB · Saudi Arabia
- HuckittaPallasite, PMG-an · Australia
- NavajoIron, IIAB · United States
- CoahuilaIron, IIAB · Mexico
- ZhaopingIron, IAB complex · China
- HenburyIron, IIIAB · Australia
- CampinorteIron, ungrouped · Brazil
- Santa LuziaIron, IIAB · Brazil
- Odessa (iron)Iron, IAB-MG · United States
- Gebel KamilIron, ungrouped · Egypt
- Casas GrandesIron, IIIAB · Mexico
- BitburgIron, IAB complex · Germany
- Quinn CanyonIron, IIIAB · United States
- CharcasIron, IIIAB · Mexico
- Santa ApoloniaIron, IIIAB · Mexico
- AlkhamasinIron, IIAB · Saudi Arabia
- Goose LakeIron, IAB-sLL · United States
- Kouga MountainsIron, IIIAB · South Africa
- MurnpeowieIron, IC · Australia
- FukangPallasite, PMG · China
- Zacatecas (1792)Iron, ungrouped · Mexico
- BilibinoIron, IIAB · Russia
- Los SaucesIron · Argentina
- TucsonIron, ungrouped · United States
- Cosby's CreekIron, IAB-MG · United States
- ImilacPallasite, PMG · Chile
- ZhiganskIron, IIIAB · Russia
- BondocMesosiderite-B4 · Philippines
- Santa RosaIron, IC · Colombia
- BrahinPallasite, PMG · Belarus
- Red RiverIron, IIIAB · United States
- SardisIron, IAB complex · United States
- Wolf CreekIron, IIIAB · Australia
- EsquelPallasite, PMG · Argentina
- Gladstone (iron)Iron, IAB-MG · Australia
- Mount DoolingIron, IC · Australia