Earth & Space Science · free reference

Part 1: Our Planet Earth

Earth's layers, Rocks and minerals, Plate tectonics, Volcanoes, Earthquakes, Landforms, weathering and erosion, Soil and Fossils and Earth's history. Every fact lists its source, and you can share a link to any topic.

#earths-layers

In short: Earth is built in layers: a thin rocky crust, a thick hot mantle, a liquid outer core and a solid inner core.[1][2]

Facts

  • Scientists divide the inside of Earth into four main layers. The inner core is in the very middle.[1]
  • The crust is the outside layer we live on. It is stiff, and it is very thin next to the layers below it.[2]
  • Under the oceans, the crust is usually only about 5 kilometers thick.[2]

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  • Under the continents, the crust is thicker: about 30 kilometers on average, and up to about 100 kilometers under large mountain ranges.[2]
  • Under the crust is the mantle. It is hot, heavy rock that is not fully solid, and it is about 2,900 kilometers thick.[2]
  • Mantle rock has more iron, magnesium and calcium in it than crust rock does.[2]
  • The core has two separate parts: an outer core and an inner core.[2]
  • The outer core is liquid. It is about 2,200 kilometers thick.[2]
  • The inner core is solid. It is about 1,250 kilometers thick.[2]
  • The core, at the center, is packed almost twice as tightly as the mantle.[2]
  • Earth's stiff outer shell of rock is called the lithosphere. Over much of the planet it is 80 kilometers thick or more.[2]
  • Below the lithosphere, scientists think there is a thin part of the mantle that can slowly move. It is called the asthenosphere.[2]

Key words in three languages

(6)
EnglishSpanishPortuguese
crust[2]corteza[3]crosta[4]
mantle[2]manto[3]manto[4]
outer core[2]núcleo externo[3]núcleo externo[4]
inner core[2]núcleo interno[3]núcleo interno[4]
lithosphere[2]litosfera[5]litosfera[4]
asthenosphere[2]astenósfera[6]astenosfera[7]

Each word cites a page that uses it.

Practice this

We do not have a lesson on this yet. The facts above are the teaching here.

Sources (7)
  1. NASA Science · Facts About Earth · science.nasa.gov/earth/facts (page updated Dec 5, 2025; checked Oct 26, 2026)
  2. U.S. Geological Survey · Inside the Earth (This Dynamic Earth) · pubs.usgs.gov/gip/dynamic/inside.html (page updated Jul 11, 2025; checked Oct 26, 2026)
  3. Universidad Complutense de Madrid, Geodivulgar · Ficha didáctica: Capas de la Tierra · ucm.es/geodivulgar/capas-de-la-tierra (checked Oct 26, 2026)
  4. Toda Matéria (Brazilian education reference) · Camadas da Terra: crosta, manto e núcleo · todamateria.com.br/camadas-da-terra (checked Oct 26, 2026)
  5. National Geographic Latinoamérica · ¿Qué son las placas tectónicas y cuántas existen en el planeta? · nationalgeographicla.com/medio-ambiente/2024/12/que-son-las-placas-tectonicas-y-cuantas-existen-en-el-planeta (page updated Dec 9, 2024; checked Oct 26, 2026)
  6. Argentina.gob.ar, Prevención Sísmica (INPRES) · Glosario · argentina.gob.ar/node/344365 (checked Oct 30, 2026)
  7. Universidade Estadual do Norte Fluminense (UENF) · A Terra em Movimento e as Placas Tectônicas · uenf.br/portal/wp-content/uploads/2026/07/A-Terra-em-Movimento-e-as-Placas-Tectonicas-combinado.pdf (checked Oct 30, 2026)

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#rocks-and-minerals

In short: Minerals are the natural building blocks of rocks. Rocks come in three families (igneous, sedimentary and metamorphic), and the rock cycle slowly turns one kind into another.[1][2][3][4][16]

Facts

  • A mineral is a natural, non-living substance. Its tiny building blocks are lined up in a regular pattern, and each mineral has its own recipe, crystal shape and properties.[1]
  • Quartz, feldspar, mica and calcite are minerals you can find in many places.[1]
  • A rock is a solid clump made of one mineral or of several minerals mixed together.[1]

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  • Granite, basalt, limestone and sandstone are well-known rocks.[1]
  • The rock cycle is the long, slow journey in which rocks move and change over time.[16]
  • Rocks keep changing. A metamorphic rock can start out as an igneous, a sedimentary or even an older metamorphic rock.[4]
  • Igneous rocks form when melted rock cools down and hardens. Their name comes from the Latin word for fire.[2]
  • Some igneous rock hardens deep underground, where the magma is trapped. Granite is one example.[2]
  • Other igneous rock hardens after the magma comes out at or near the surface. Basalt and obsidian are examples.[2]
  • Sedimentary rocks are made from bits of older rock or from the remains of things that were once alive. The bits pile up on the surface and slowly become rock.[3]
  • Sandstone, limestone and shale are sedimentary rocks.[3]
  • Shale is a rock made mostly from clay.[3]
  • Weathering loosens pieces of rock. Rivers often carry them away to lakes and oceans.[3]
  • When these bits get buried deep, they are pressed and cemented together into solid rock.[3]
  • A metamorphic rock began as a different kind of rock and was changed a great deal.[4]
  • High heat, high pressure, or both are what change them.[4]
  • Marble, quartzite, schist and gneiss are metamorphic rocks.[4]
  • Marble is a metamorphic rock that people have long used for statues and buildings.[4]
  • Igneous rock forms when hot, melted rock (magma) cools and hardens.[16][2]

Key words in three languages

(14)
EnglishSpanishPortuguese
rock[1]roca[5]rocha[6]
mineral[1]mineral[5]mineral[7]
igneous rock[2]roca ígnea[5]rocha ígnea[7]
sedimentary rock[3]roca sedimentaria[5]rocha sedimentar[7]
metamorphic rock[4]roca metamórfica[5]rocha metamórfica[7]
rock cycle[16]ciclo de las rocas[17]ciclo das rochas[7]
sediment[18]sedimento[5]sedimento[7]
magma[8]magma[9]magma[10]
granite[2]granito[11]granito[7]
basalt[2]basalto[5]basalto[7]
marble[4]mármol[12]mármore[7]
sandstone[3]arenisca[13]arenito[7]
limestone[3]caliza[14]calcário[7]
deposition[18]sedimentación[15]sedimentação[7]

Each word cites a page that uses it.

More practice

(6)

Members-only items are marked. The science game and the worksheets by grade are free.

Sources (18)
  1. U.S. Geological Survey · What is the difference between a rock and a mineral? · usgs.gov/faqs/what-difference-between-a-rock-and-a-mineral (page updated Nov 7, 2024; checked Oct 26, 2026)
  2. U.S. Geological Survey · What are igneous rocks? · usgs.gov/faqs/what-are-igneous-rocks (checked Oct 26, 2026)
  3. U.S. Geological Survey · What are sedimentary rocks? · usgs.gov/faqs/what-are-sedimentary-rocks (checked Oct 26, 2026)
  4. U.S. Geological Survey · What are metamorphic rocks? · usgs.gov/faqs/what-are-metamorphic-rocks (page updated Sep 9, 2026; checked Oct 26, 2026)
  5. Servicio Geológico Colombiano, Museo Geológico José Royo Gómez · Folleto: Rocas · www2.sgc.gov.co/museo-geologico/recursos-educativos/Documents/Folleto_Rocas.pdf (checked Oct 26, 2026)
  6. Toda Matéria (Brazilian education reference) · Intemperismo · todamateria.com.br/intemperismo (checked Oct 26, 2026)
  7. Toda Matéria (Brazilian education reference) · Ciclo das Rochas: o que é e como ocorre · todamateria.com.br/ciclo-das-rochas (checked Oct 26, 2026)
  8. U.S. Geological Survey, Volcano Hazards Program · About Volcanoes · usgs.gov/programs/VHP/about-volcanoes (checked Oct 26, 2026)
  9. Instituto Geográfico Nacional (España) · Glosario de términos volcánicos · ign.es/web/ign/portal/vlc-glosario (checked Oct 26, 2026)
  10. Toda Matéria (Brazilian education reference) · Vulcão: o que é, como se forma e quais suas partes · todamateria.com.br/vulcao (checked Oct 26, 2026)
  11. RAE-ASALE, Diccionario de la lengua española · granito · dle.rae.es/granito (checked Oct 26, 2026)
  12. RAE-ASALE, Diccionario de la lengua española · mármol · dle.rae.es/m%C3%A1rmol (checked Oct 26, 2026)
  13. RAE-ASALE, Diccionario de la lengua española · arenisco · dle.rae.es/arenisco (checked Oct 26, 2026)
  14. RAE-ASALE, Diccionario de la lengua española · calizo · dle.rae.es/calizo (checked Oct 26, 2026)
  15. RAE-ASALE, Diccionario de la lengua española · sedimentación · dle.rae.es/sedimentaci%C3%B3n (checked Oct 26, 2026)
  16. National Park Service, Chesapeake and Ohio Canal · Activity 1: Types of Rocks · nps.gov/choh/learn/kidsyouth/activity-1-types-of-rocks.htm (checked Oct 30, 2026)
  17. Utah Geological Survey (Servicio Geológico de Utah) · El ciclo de las rocas (Public Information Series 101) · ugspub.nr.utah.gov/publications/public_information/PI-101.pdf (checked Oct 30, 2026)
  18. National Park Service · Erosion: Water, Wind & Weather (About) · nps.gov/subjects/erosion/about.htm (page updated Sep 12, 2019; checked Oct 30, 2026)

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#plate-tectonics

In short: Earth's outer shell is broken into giant plates that move very slowly. Where they pull apart, push together or slide past each other, the land changes.[1][2]

Facts

  • Earth's outer shell is cracked into giant pieces, a bit like a puzzle. The pieces are tectonic plates, and their edges are plate boundaries.[1]
  • Plate edges are rough, so they can catch on each other while the rest of each plate keeps going.[1]
  • Most of the action happens in narrow strips where plates meet.[2]

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  • At a divergent boundary, two plates pull away from each other.[2]
  • At a convergent boundary, two plates push toward each other, and old crust gets recycled.[2]
  • At a transform boundary, two plates grind past each other sideways.[2]
  • Iceland sits where the North American and Eurasian Plates are spreading apart, so the island is slowly splitting.[2]
  • The Mid-Atlantic Ridge spreads open by about 2.5 centimeters each year on average.[2]
  • The Pacific Plate has been sliding past the North American Plate for about 10 million years.[2]
  • Long ago the continents were joined as one huge landmass called Pangaea. In Greek, the name means "all lands."[3]
  • Pangaea started to come apart between about 225 and 200 million years ago.[3]
  • The idea that continents drift was first put forward by Alfred Wegener, a German weather scientist.[3]
  • At that time, most scientists thought continents and oceans never moved.[3]

Key words in three languages

(8)
EnglishSpanishPortuguese
lithosphere[4]litosfera[5]litosfera[6]
asthenosphere[4]astenósfera[8]astenosfera[9]
plate tectonics[2]tectónica de placas[5]tectônica de placas[9]
tectonic plate[1]placa tectónica[5]placa tectônica[6]
divergent boundary[2]límite divergente[5]limite divergente[7]
convergent boundary[2]límite convergente[5]limite convergente[9]
transform boundary[2]límite transformante[5]limite transformante[9]
Pangaea[3]Pangea[10]Pangeia[7]

Each word cites a page that uses it.

More practice

(3)

Members-only items are marked. The science game and the worksheets by grade are free.

Sources (10)
  1. U.S. Geological Survey, Earthquake Hazards Program · The Science of Earthquakes · usgs.gov/programs/earthquake-hazards/science-earthquakes (checked Oct 26, 2026)
  2. U.S. Geological Survey · Understanding plate motions (This Dynamic Earth) · pubs.usgs.gov/publications/text/understanding.html (page updated Sep 15, 2014; checked Oct 26, 2026)
  3. U.S. Geological Survey · Historical perspective (This Dynamic Earth) · pubs.usgs.gov/gip/dynamic/historical.html (page updated Aug 7, 2012; checked Oct 26, 2026)
  4. U.S. Geological Survey · Inside the Earth (This Dynamic Earth) · pubs.usgs.gov/gip/dynamic/inside.html (page updated Jul 11, 2025; checked Oct 26, 2026)
  5. National Geographic Latinoamérica · ¿Qué son las placas tectónicas y cuántas existen en el planeta? · nationalgeographicla.com/medio-ambiente/2024/12/que-son-las-placas-tectonicas-y-cuantas-existen-en-el-planeta (page updated Dec 9, 2024; checked Oct 26, 2026)
  6. Toda Matéria (Brazilian education reference) · Camadas da Terra: crosta, manto e núcleo · todamateria.com.br/camadas-da-terra (checked Oct 26, 2026)
  7. Toda Matéria (Brazilian education reference) · Placas tectônicas · todamateria.com.br/placas-tectonicas (checked Oct 26, 2026)
  8. Argentina.gob.ar, Prevención Sísmica (INPRES) · Glosario · argentina.gob.ar/node/344365 (checked Oct 30, 2026)
  9. Universidade Estadual do Norte Fluminense (UENF) · A Terra em Movimento e as Placas Tectônicas · uenf.br/portal/wp-content/uploads/2026/07/A-Terra-em-Movimento-e-as-Placas-Tectonicas-combinado.pdf (checked Oct 30, 2026)
  10. USGS, La Tierra Dinámica (Kious y Tilling), versión en español en LibreTexts · Perspectiva histórica · espanol.libretexts.org/Bookshelves/Geociencias/Geolog%C3%ADa/La_Tierra_Din%C3%A1mica_(Kious_y_Labranza)/01%3A_Perspectiva_hist%C3%B3rica (checked Oct 30, 2026)

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#volcanoes

In short: A volcano is an opening where lava, small rocks and steam come out. Magma collects in a chamber, rises through vents and comes out as lava. Shield volcanoes, cinder cones and stratovolcanoes have different shapes.[1][2][3]

Facts

  • A volcano is an opening in Earth's surface where lava, small bits of rock and steam burst out.[1]
  • Melted rock that is still underground is called magma.[1]
  • When magma comes out of a volcano, we call it lava.[2]

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More facts

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  • Magma weighs less than the solid rock around it, so it rises and gathers in underground pools called magma chambers.[2]
  • Some of the magma finally forces its way up through openings and cracks to the surface.[2]
  • A vent is any opening in the ground where magma or volcanic gas comes out.[4]
  • At the top of many volcanoes there is a bowl-shaped dip called a crater. It shows where the vent is.[1]
  • A stratovolcano usually has many vents. Some of them open on the sides of the mountain, not only at the top.[3]
  • A lava flow is a river of melted rock that spills or creeps out of a vent.[5]
  • On gentle slopes, most lava flows creep along at less than 1 kilometer per hour, slow enough for people to move out of the way.[5]
  • Volcanic ash is made of tiny pieces of broken rock, each smaller than 2 millimeters.[6]
  • Big explosive eruptions can blast ash so high that it reaches the stratosphere.[6]
  • An eruption column is the tall tower of gas and rock bits that shoots straight up from a vent. Higher up, it spreads sideways into an ash cloud.[7]
  • Not every eruption is a big blast. Some are explosive and some are calm.[2]
  • Shield volcanoes are built almost completely from runny lava flows.[1]
  • They are broad and shaped like a shield, and they grow from one runny-lava eruption after another.[8]
  • Kīlauea, on the Island of Hawaiʻi, is a shield volcano.[9]
  • Cinder cones are the simplest kind of volcano.[1]
  • A cinder cone is a steep, cone-shaped hill made of hardened lava pieces that rain down around the vent during one eruption.[10]
  • Parícutin, a famous cinder cone in Mexico, started growing in a farmer's cornfield in 1943.[10]
  • Stratovolcanoes (also called composite volcanoes) are tall, steep cones built from thick lava, rock pieces and hot flows of ash and gas.[3]
  • Some of the biggest, most famous mountains on Earth are stratovolcanoes.[1]
  • Scientists at the USGS keep watch on more than 160 volcanoes in the United States that are active or could become active.[1]

Key words in three languages

(14)
EnglishSpanishPortuguese
magma[1]magma[11]magma[12]
volcano[1]volcán[11]vulcão[12]
lava[2]lava[11]lava[13]
magma chamber[2]cámara magmática[11]câmara magmática[13]
vent (main vent)[2]chimenea[14]chaminé[13]
side vent (flank vent)[3]chimenea secundaria[15]chaminé secundária[16]
crater[1]cráter[14]cratera[12]
lava flow[5]colada de lava[11]derrame de lava[13]
volcanic ash[6]ceniza volcánica[11]cinzas vulcânicas[13]
eruption column (ash cloud)[7]columna eruptiva[17]coluna eruptiva[18]
shield volcano[1]volcán en escudo[17]vulcão-escudo[13]
cinder cone[1]cono de escoria[11]cone de cinzas[13]
stratovolcano (composite volcano)[3]estratovolcán[17]estratovulcão[13]
eruption[2]erupción[11]erupção[13]

Each word cites a page that uses it.

More practice

(6)

Members-only items are marked. The science game and the worksheets by grade are free.

Sources (18)
  1. U.S. Geological Survey, Volcano Hazards Program · About Volcanoes · usgs.gov/programs/VHP/about-volcanoes (checked Oct 26, 2026)
  2. U.S. Geological Survey · How do volcanoes erupt? · usgs.gov/faqs/how-do-volcanoes-erupt (checked Oct 26, 2026)
  3. U.S. Geological Survey, Volcano Hazards Program Glossary · Stratovolcano · volcanoes.usgs.gov/vsc/glossary/stratovolcano.html (page updated Jul 8, 2015; checked Oct 26, 2026)
  4. U.S. Geological Survey, Volcano Hazards Program Glossary · Vent · volcanoes.usgs.gov/vsc/glossary/vent.html (page updated Aug 16, 2011; checked Oct 26, 2026)
  5. U.S. Geological Survey, Volcano Hazards Program · Lava flows destroy everything in their path · usgs.gov/programs/VHP/lava-flows-destroy-everything-their-path (checked Oct 26, 2026)
  6. National Park Service · Volcanic Ash, Tephra Fall, and Fallout Deposits · nps.gov/articles/000/volcanic-ash-tephra-fall-and-fallout-deposits.htm (page updated Apr 18, 2023; checked Oct 26, 2026)
  7. U.S. Geological Survey, Volcano Hazards Program Glossary · Eruption column · volcanoes.usgs.gov/vsc/glossary/eruption_column.html (checked Oct 26, 2026)
  8. U.S. Geological Survey, Volcano Hazards Program Glossary · Shield volcano · volcanoes.usgs.gov/vsc/glossary/shield_volcano.html (page updated Sep 19, 2013; checked Oct 26, 2026)
  9. U.S. Geological Survey · Kīlauea · usgs.gov/volcanoes/kilauea (checked Oct 26, 2026)
  10. U.S. Geological Survey, Volcano Hazards Program Glossary · Cinder cone · volcanoes.usgs.gov/vsc/glossary/cinder_cone.html (page updated Jun 30, 2015; checked Oct 26, 2026)
  11. Instituto Geográfico Nacional (España) · Glosario de términos volcánicos · ign.es/web/ign/portal/vlc-glosario (checked Oct 26, 2026)
  12. Toda Matéria (Brazilian education reference) · Vulcão: o que é, como se forma e quais suas partes · todamateria.com.br/vulcao (checked Oct 26, 2026)
  13. InfoEscola (Brazilian education reference) · Erupção vulcânica · infoescola.com/geologia/erupcao-vulcanica (checked Oct 26, 2026)
  14. Universidad Complutense de Madrid, Geodivulgar · El volcán · ucm.es/geodivulgar/el-volcan (checked Oct 26, 2026)
  15. EcoExploratorio, Museo de Ciencias de Puerto Rico · Estructura (Volcanes, Amenazas naturales) · ecoexploratorio.org/amenazas-naturales/volcanes/estructura (page updated Aug 12, 2022; checked Oct 26, 2026)
  16. Universidade Federal do Pampa (UNIPAMPA), Repositório Institucional · Sequência didática com a temática vulcão: uma proposta de ensino de ciências para o ensino fundamental (A. S. Zeidler, TCC, 2018) · repositorio.unipampa.edu.br/bitstreams/4f5ff3ba-acb2-4f1e-854a-79d37d334420/download (checked Oct 26, 2026)
  17. SEGEMAR, Observatorio Argentino de Vigilancia Volcánica (Argentina) · Cuando hablamos de volcanes (glosario) · oavv.segemar.gob.ar/descargas/GLOSARIO%20OAVV-SEGEMAR.pdf (checked Oct 26, 2026)
  18. Serviço Geológico do Brasil (SGB-CPRM), SGBeduca · Os Vulcões (Caderno do Professor, M. L. Besser) · sgbeduca.sgb.gov.br/media/professores/osvulcoes.pdf (checked Oct 26, 2026)

See something we should correct about “Volcanoes”? Tell us.

#earthquakes

In short: Earthquakes happen when blocks of rock suddenly slip along a fault. Scientists measure them with seismographs, and families can practice Drop, Cover, Hold On.[1][2]

Facts

  • An earthquake happens when two huge blocks of ground suddenly slip past each other.[1]
  • The crack where the blocks slip is called a fault.[1]
  • The spot underground where an earthquake begins is the hypocenter.[1]

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  • The place on the surface right above that spot is the epicenter.[1]
  • Scientists record earthquakes with instruments called seismographs.[1]
  • How big an earthquake is gets described by a number called its magnitude.[1]
  • Sometimes small quakes, called foreshocks, come before a bigger one in the same place.[1]
  • Smaller quakes that come after the main one, in the same area, are called aftershocks.[1]
  • If the ground shakes: get down on your hands and knees, protect your head and neck with your arms, and hold on to something sturdy until the shaking ends.[2]
  • Do not stand in a doorway, and do not run outside during the shaking.[2]
  • If you are in bed, stay there and put a pillow over your head and neck.[2]

Key words in three languages

(7)
EnglishSpanishPortuguese
earthquake[1]terremoto / sismo[3]terremoto / sismo[4]
fault[1]falla[5]falha[4]
epicenter[1]epicentro[3]epicentro[4]
hypocenter[1]hipocentro[3]hipocentro[4]
seismograph[1]sismógrafo[3]sismógrafo[6]
magnitude[1]magnitud[3]magnitude[4]
aftershock[1]réplica[3]réplica[7]

Each word cites a page that uses it.

More practice

(3)

Members-only items are marked. The science game and the worksheets by grade are free.

Sources (7)
  1. U.S. Geological Survey, Earthquake Hazards Program · The Science of Earthquakes · usgs.gov/programs/earthquake-hazards/science-earthquakes (checked Oct 26, 2026)
  2. FEMA, Ready.gov · Earthquakes · ready.gov/earthquakes (checked Oct 26, 2026)
  3. Argentina.gob.ar, Prevención Sísmica (SEGEMAR) · Glosario · argentina.gob.ar/node/344365 (checked Oct 26, 2026)
  4. Toda Matéria (Brazilian education reference) · Terremoto · todamateria.com.br/terremoto (checked Oct 26, 2026)
  5. RAE-ASALE, Diccionario de la lengua española · falla · dle.rae.es/falla (checked Oct 26, 2026)
  6. Dicionário Priberam da Língua Portuguesa · sismógrafo · dicionario.priberam.org/sism%C3%B3grafo (checked Oct 26, 2026)
  7. Dicionário Priberam da Língua Portuguesa · réplica · dicionario.priberam.org/r%C3%A9plica (checked Oct 26, 2026)

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#landforms-weathering-erosion

In short: Weathering breaks rock apart, erosion carries the pieces away, and deposition drops them somewhere new. Over time this shapes mountains, valleys, canyons and plains.[20][1]

Facts

  • A landform is a shape of the land surface. Mountains, hills, plateaus, plains, valleys and canyons are all landforms.[1]
  • A hill rises above the land around it, but it is smaller than a mountain. There is no official rule for how tall a hill can be before it is called a mountain.[1][27]
  • A plateau is a big, fairly flat area that sits higher than the land around it.[26]

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  • A plain is a large area of flat land.[1]
  • A valley is a long, low stretch of land between hills or mountains.[1]
  • A canyon is a deep, narrow valley with steep walls.[1][28]
  • Many mountain ranges, like the Himalayas and the Andes, were pushed up where tectonic plates collide.[21]
  • Weathering is when bits of rock are loosened but stay in place.[20]
  • Rock can be loosened in two ways: mechanically (broken into pieces) or chemically (changed by chemicals).[20]
  • Once the loose bits are moved away by flowing water, wind or ice, it is called erosion.[20]
  • Water, wind, ice and gravity are the forces that wear down the land and move it.[20]
  • Rivers carry sediment and drop it in lakes and oceans.[22]
  • Wind can move loose bits of rock and soil too.[20]
  • Flowing ice, like a glacier, can carry rock away too.[20]
  • Rock and soil can also move down a slope, pulled by gravity. Scientists call this mass wasting.[23]
  • Deposition is when eroded sediment drops out of the moving water, wind or ice and builds up in a new place.[20]
  • A river delta forms where a river drops sediment at its mouth faster than waves and tides can carry it away.[24]
  • The Colorado River carved the Grand Canyon. It has been cutting into the rock for the past five to six million years.[25]

Key words in three languages

(11)
EnglishSpanishPortuguese
sediment[20]sedimento[2]sedimento[3]
landform[1]relieve[4]forma de relevo[5]
mountain[21]montaña[6]montanha[5]
plateau[26]meseta[7]planalto[5]
plain[1]llanura[8]planície[5]
valley[1]valle[9]vale[10]
canyon[25]cañón[11]cânion[12]
weathering[20]meteorización[13]intemperismo[14]
erosion[20]erosión[15]erosão[5]
deposition[20]sedimentación[16]sedimentação[3]
glacier[17]glaciar[18]geleira[19]

Each word cites a page that uses it.

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(8)

Members-only items are marked. The science game and the worksheets by grade are free.

Sources (28)
  1. National Park Service, Scotts Bluff National Monument · Geologic Landforms · nps.gov/scbl/learn/nature/geologic-landforms.htm (page updated Aug 17, 2026; checked Oct 30, 2026)
  2. Servicio Geológico Colombiano, Museo Geológico José Royo Gómez · Folleto: Rocas · www2.sgc.gov.co/museo-geologico/recursos-educativos/Documents/Folleto_Rocas.pdf (checked Oct 26, 2026)
  3. Toda Matéria (Brazilian education reference) · Ciclo das Rochas: o que é e como ocorre · todamateria.com.br/ciclo-das-rochas (checked Oct 26, 2026)
  4. RAE-ASALE, Diccionario de la lengua española · relieve · dle.rae.es/relieve (checked Oct 26, 2026)
  5. Toda Matéria (Brazilian education reference) · Formas de relevo · todamateria.com.br/formas-de-relevo (checked Oct 26, 2026)
  6. RAE-ASALE, Diccionario de la lengua española · montaña · dle.rae.es/monta%C3%B1a (checked Oct 26, 2026)
  7. RAE-ASALE, Diccionario de la lengua española · meseta · dle.rae.es/meseta (checked Oct 26, 2026)
  8. RAE-ASALE, Diccionario de la lengua española · llanura · dle.rae.es/llanura (checked Oct 26, 2026)
  9. RAE-ASALE, Diccionario de la lengua española · valle · dle.rae.es/valle (checked Oct 26, 2026)
  10. Dicionário Priberam da Língua Portuguesa · vale · dicionario.priberam.org/vale (checked Oct 26, 2026)
  11. RAE-ASALE, Diccionario de la lengua española · cañón · dle.rae.es/ca%C3%B1%C3%B3n (checked Oct 26, 2026)
  12. Dicionário Priberam da Língua Portuguesa · cânion · dicionario.priberam.org/c%C3%A2nion (checked Oct 26, 2026)
  13. RAE-ASALE, Diccionario de la lengua española · meteorización · dle.rae.es/meteorizaci%C3%B3n (checked Oct 26, 2026)
  14. Toda Matéria (Brazilian education reference) · Intemperismo · todamateria.com.br/intemperismo (checked Oct 26, 2026)
  15. RAE-ASALE, Diccionario de la lengua española · erosión · dle.rae.es/erosi%C3%B3n (checked Oct 26, 2026)
  16. RAE-ASALE, Diccionario de la lengua española · sedimentación · dle.rae.es/sedimentaci%C3%B3n (checked Oct 26, 2026)
  17. National Snow and Ice Data Center (University of Colorado Boulder) · Glaciers · nsidc.org/learn/parts-cryosphere/glaciers (checked Oct 26, 2026)
  18. U.S. Geological Survey · El Ciclo del Agua (General Information Product 146) · water.usgs.gov/edu/watercyclekids/download/watercycle-kids-spanish.pdf (checked Oct 26, 2026)
  19. U.S. Geological Survey, Water Science School · O Ciclo d'água (The Water Cycle, Portuguese) · usgs.gov/water-science-school/science/o-ciclo-dagua-water-cycle-portuguese (page updated Oct 4, 2019; checked Oct 26, 2026)
  20. National Park Service · Erosion: Water, Wind & Weather (About) · nps.gov/subjects/erosion/about.htm (page updated Sep 12, 2019; checked Oct 30, 2026)
  21. U.S. Geological Survey · Understanding plate motions (This Dynamic Earth) · pubs.usgs.gov/gip/dynamic/understanding.html (page updated Jul 11, 2025; checked Oct 30, 2026)
  22. U.S. Geological Survey · What are sedimentary rocks? · usgs.gov/faqs/what-are-sedimentary-rocks (checked Oct 30, 2026)
  23. National Park Service · Mass Wasting · nps.gov/subjects/erosion/mass-wasting.htm (page updated Sep 11, 2019; checked Oct 30, 2026)
  24. National Park Service · Delta Landforms · home.nps.gov/articles/delta-landforms.htm (page updated Mar 20, 2019; checked Oct 30, 2026)
  25. National Park Service, Grand Canyon National Park · Geology · nps.gov/grca/learn/nature/grca-geology.htm (page updated Sep 16, 2026; checked Oct 30, 2026)
  26. National Park Service, National Natural Landmarks Program · Plateaus and Mesas · nps.gov/subjects/nnlandmarks/plateaus-and-mesas.htm (page updated Dec 3, 2025; checked Oct 30, 2026)
  27. U.S. Geological Survey · What is the difference between “mountain”, “hill”, and “peak”; “lake” and “pond”; or “river” and “creek?” · usgs.gov/faqs/what-difference-between-mountain-hill-and-peak-lake-and-pond-or-river-and-creek (checked Oct 30, 2026)
  28. National Park Service · Canyons & Canyonlands · nps.gov/subjects/canyons/index.htm (page updated Feb 5, 2019; checked Oct 30, 2026)

See something we should correct about “Landforms, weathering and erosion”? Tell us.

#soil

In short: Soil is a living mix of minerals, water, air and once-living material. It forms in layers called horizons and is what plants grow in.[1]

Facts

  • Soil is a mix of minerals, water, air, bits of once-living things, and huge numbers of tiny living things.[1]
  • Soil forms on top of the land, so scientists sometimes call it the skin of the Earth.[1]
  • If you dig down, soil comes in layers called horizons. Most soils have three main ones, named A, B and C, and some also have an O layer on top.[1]

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(5)
  • The A horizon is topsoil: mostly minerals, mixed with material from living things.[1]
  • The O horizon is mostly rotting leaves and other once-living material, also called humus.[1]
  • Plants grow in soil, and life on Earth depends on it.[1]
  • Soil recycles nutrients, such as carbon, so living things can use them again and again.[1]
  • Soil works like a living filter that cleans water before it reaches underground stores of water.[1]

Key words in three languages

(3)
EnglishSpanishPortuguese
soil[1]suelo[2]solo[3]
humus[1]humus[4]húmus[5]
aquifer[1]acuífero[6]aquífero[7]

Each word cites a page that uses it.

More practice

(3)

Members-only items are marked. The science game and the worksheets by grade are free.

Sources (7)
  1. Soil Science Society of America, Soils 4 Kids · All About Soil · soils4kids.org/about (checked Oct 26, 2026)
  2. RAE-ASALE, Diccionario de la lengua española · suelo · dle.rae.es/suelo (checked Oct 26, 2026)
  3. Toda Matéria (Brazilian education reference) · Intemperismo · todamateria.com.br/intemperismo (checked Oct 26, 2026)
  4. RAE-ASALE, Diccionario de la lengua española · humus · dle.rae.es/humus (checked Oct 26, 2026)
  5. Dicionário Priberam da Língua Portuguesa · húmus · dicionario.priberam.org/h%C3%BAmus (checked Oct 26, 2026)
  6. U.S. Geological Survey · El Ciclo del Agua (General Information Product 146) · water.usgs.gov/edu/watercyclekids/download/watercycle-kids-spanish.pdf (checked Oct 26, 2026)
  7. U.S. Geological Survey, Water Science School · O Ciclo d'água (The Water Cycle, Portuguese) · usgs.gov/water-science-school/science/o-ciclo-dagua-water-cycle-portuguese (page updated Oct 4, 2019; checked Oct 26, 2026)

See something we should correct about “Soil”? Tell us.

#fossils-and-earths-history

In short: Fossils are remains or traces of ancient life, usually buried quickly in sediment. Rock layers stack up like pages of a history book, with the oldest at the bottom.[9][1]

Facts

  • Fossils are the remains or traces of living things from long ago.[9]
  • Fossils of real body parts, such as bones, shells or leaves, are called body fossils.[9][10]
  • Trace fossils, such as footprints and burrows, record what a living thing did, not the living thing itself.[9]

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  • The most important step to become a fossil is to be buried quickly after death, usually in layers of sediment.[9][10]
  • Over time, minerals in groundwater can replace the original shell or bone.[9]
  • Scientists who study fossils are paleontologists.[9]
  • Sediment settling on the bottom of a lake or sea can bury animals and plants, and their skeletons and pieces can turn into fossils.[1]
  • Sedimentary rocks form in layers, and each layer is like a page in Earth's history book.[1]
  • In a stack of rock layers, a lower layer is older than the layers above it.[1]
  • This rule lets scientists tell which layers, and which fossils in them, are older or younger.[1]
  • Scientists estimate that Earth is about 4.54 billion years old.[2]
  • To work this out, they assume Earth formed at the same time as the other solid objects in the solar system, such as meteorites.[2]

Key words in three languages

(4)
EnglishSpanishPortuguese
sedimentary rock[3]roca sedimentaria[4]rocha sedimentar[5]
sediment[10]sedimento[4]sedimento[5]
fossil[9]fósil[4]fóssil[6]
paleontologist[9]paleontólogo[7]paleontólogo[8]

Each word cites a page that uses it.

More practice

(6)

Members-only items are marked. The science game and the worksheets by grade are free.

Sources (10)
  1. U.S. Geological Survey · Rocks and Layers (Fossils, Rocks, and Time) · pubs.usgs.gov/gip/fossils/rocks-layers.html (page updated Aug 14, 1997; checked Oct 26, 2026)
  2. U.S. Geological Survey · Age of the Earth (Geologic Time) · pubs.usgs.gov/gip/geotime/age.html (page updated Jul 9, 2007; checked Oct 26, 2026)
  3. U.S. Geological Survey · What are sedimentary rocks? · usgs.gov/faqs/what-are-sedimentary-rocks (checked Oct 26, 2026)
  4. Servicio Geológico Colombiano, Museo Geológico José Royo Gómez · Folleto: Rocas · www2.sgc.gov.co/museo-geologico/recursos-educativos/Documents/Folleto_Rocas.pdf (checked Oct 26, 2026)
  5. Toda Matéria (Brazilian education reference) · Ciclo das Rochas: o que é e como ocorre · todamateria.com.br/ciclo-das-rochas (checked Oct 26, 2026)
  6. Dicionário Priberam da Língua Portuguesa · fóssil · dicionario.priberam.org/f%C3%B3ssil (checked Oct 26, 2026)
  7. RAE-ASALE, Diccionario de la lengua española · paleontólogo · dle.rae.es/paleont%C3%B3logo (checked Oct 26, 2026)
  8. Dicionário Priberam da Língua Portuguesa · paleontólogo · dicionario.priberam.org/paleont%C3%B3logo (checked Oct 26, 2026)
  9. National Park Service, National Fossil Day · Frequently Asked Questions · nps.gov/subjects/fossilday/faq.htm (checked Oct 30, 2026)
  10. USDA Forest Service · Paleontology: Traces of Past Life (FS-1058) · fs.usda.gov/sites/default/files/media_wysiwyg/paleontology-traces-of-past-life.pdf (checked Oct 30, 2026)

See something we should correct about “Fossils and Earth's history”? Tell us.

Free printables for this part

Printables that go with the topics on this page.

Printables with a black and white button also come in a low-ink version, good for coloring and filling in.

  • Label the layers of the Earth

    Free PDFGrades 3–5

    Color

  • The rock cycle

    Free PDFGrades 4–7

    Color

  • Label the parts of a volcano

    Free PDFGrades 3–5

    Color

  • Color a volcano cutaway

    Free PDFGrades 2–4

    Color