ACT Science vocabulary: earth, space and environment.
20 terms the ACT Science section expects you to already know when a passage turns to earth, space and environment — each with a definition, an example sentence, and a memory cue.
ACT Science does not test whether you can define these words — it tests whether you can read a figure fast enough, and an unfamiliar term is what stops you. The section gives you well under a minute per question, so the goal here is recognition, not recall: you want to meet these terms in a question stem and know immediately what they point to.
Read the definition, then the example, then the memory cue. Come back a few days later and cover the definitions — recalling a term cold is what fixes it, and rereading it is not.
The 20 terms
Alphabetical. Everything in the Earth, Space & Environment guide.
01
acreagenoun
An area of land, typically measured in acres
The disputed acreage along the border became the flashpoint for a decades-long territorial conflict.
Memory cueAcreage measures how many acre-sized squares cover a piece of land.
02
aquifernoun
A body of permeable rock that can contain or transmit groundwater
The massive aquifer beneath the Great Plains supplies drinking water to millions but is being depleted faster than it recharges.
Memory cueAn aquifer is an underground rocky sponge storing and transmitting water.
03
aridadjective
extremely dry (often describing climate or land); lacking in interest or excitement.
Only drought-resistant shrubs survived in the arid valley, where rain had not fallen for months.
Memory cueAn arid landscape is cracked and extremely dry; an arid lecture feels equally lifeless.
04
atmospherenoun
The layer or collection of gases surrounding a planet or other celestial body.
Earth's atmosphere absorbs some harmful radiation while retaining heat needed for liquid water at the surface.
Memory cueThe atmosphere is a planet's enormous gas blanket wrapped around its surface.
05
climatenoun
The long-term pattern of weather conditions typical of a region or the planet.
The region's climate became drier across decades even though individual years still included severe storms.
Memory cueWeather is today's outfit; climate is the whole long-term wardrobe.
06
crateredadjective
Having craters (bowl-shaped depressions) on the surface
The cratered surface of the moon preserves a record of billions of years of asteroid impacts.
Memory cueA cratered moon wears bowl-shaped dents across its surface.
07
desiccateverb
to dry out thoroughly; to remove moisture from.
Weeks of intense heat desiccated the unprotected soil until deep cracks appeared, providing concrete clues from which a careful reader can infer the unfamiliar term.
Memory cueDesiccate a leaf until all moisture leaves and it becomes dry and brittle.
08
erosionnoun
The removal and transport of rock or soil by water, wind, ice, or gravity.
Riverbank erosion accelerated when flooding carried loosened soil downstream after vegetation had been removed.
Memory cueErosion is Earth's slow conveyor belt carrying worn material away from its source.
09
fallowadjective
(Of farmland) plowed and harrowed but left unsown for a period to restore its fertility
The farmer left the eastern fields fallow for a season, allowing the depleted soil to recover its nutrients.
Memory cueA fallow field rests unsown so its fertility can recover.
10
glaciersnoun (plural)
Massive, slow-moving bodies of ice formed from compacted snow on land
As glaciers retreat due to rising temperatures, they expose landscapes that have been buried under ice for millennia.
Memory cueGlaciers are immense rivers of compacted ice moving slowly across land.
11
inundateverb
To overwhelm someone with things to be dealt with; to flood
After the announcement, the office was inundated with phone calls from concerned citizens.
Memory cueTo inundate an inbox, flood it with more messages than manageable.
12
meteorologynoun
The scientific study of the atmosphere and weather
Advances in meteorology have dramatically improved the accuracy of weather forecasts over the past fifty years.
Memory cueMeteorology studies the atmosphere’s weather, winds, clouds, and storms.
13
orbitnoun
The curved path an object follows around another body because of gravity.
The satellite remained in orbit because gravity continually bent its forward motion toward Earth.
Memory cueAn orbit is a gravity-curved racetrack looping around a larger body.
14
parchedadjective
extremely dry; thirsty.
After crossing the exposed ridge, the parched hikers eagerly refilled their empty water bottles.
Memory cueA parched throat and cracked ground both desperately need water.
15
radiocarbonnoun/adjective
Relating to carbon-14 dating, a method of determining the age of organic materials
Radiocarbon dating placed the artifacts at approximately 3,000 years old, consistent with the Bronze Age settlement.
Memory cueRadiocarbon dating reads carbon-14’s clock to estimate organic material’s age.
16
sedimentaryadjective
Relating to or formed from sediment (material deposited by water, wind, or glaciers)
Fossils are most commonly found in sedimentary rock, where layers of sand and mud preserved organisms over millennia.
Memory cueSedimentary rock forms as deposited layers of sediment press together.
17
tectonicadjective
Relating to the structure and movement of large sections of Earth's crust.
Tectonic motion along the plate boundary produced frequent earthquakes and slowly raised the mountain range.
Memory cueTectonic plates are giant moving tiles fitted across Earth's outer shell.
18
temperateadjective
Relating to moderate climatic regions between the tropics and the poles
The temperate forests of the Pacific Northwest support some of the tallest trees and most diverse fungal communities on Earth.
Memory cueTemperate climates occupy the moderate zones between tropics and poles.
19
unearthedverb (past participle)
Dug up from the ground; discovered through excavation
Construction workers accidentally unearthed a cache of Roman coins buried beneath the foundation of a medieval church.
Memory cueArchaeologists unearthed the artifact by digging it out of the ground.
20
unvegetatedadjective
Having no vegetation; bare of plant life
The unvegetated slopes above the treeline are subject to severe erosion during heavy rainstorms.
Memory cueUnvegetated ground is bare soil with no plant cover.
Knowing the words is step one — reading the figure is step two.
Test Ninjas puts these terms back into real Science passages — full-length ACT practice tests, a complete Science course, and an explanation on every question.
