Grade 8 Science Vocabulary

Shaping Earth’s Surface & Geologic Time

The forces that build up and wear down land, and how rock layers and fossils record Earth’s history.

Ohio science standards in this unit

8.ESS.3 · Shaping the surfaceA combination of constructive and destructive geologic processes formed Earth's surface.
8.ESS.4 · Geologic recordEvidence of the dynamic changes of Earth's surface through time is found in the geologic record.

Definitions are written in plain language to support WIDA's Standard 4 (Science) English Language Development standard.

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constructive force: A process that builds up land, like volcanoes or deposition.
destructive force: A process that wears down land, like erosion or weathering.
hydrosphere: All the water on and near Earth’s surface.
lithosphere: Earth’s solid outer layer: the crust and the top of the mantle.
topography: The shape and height of the land’s surface.
floodplain: Flat land next to a river that is covered with water when the river floods.
discharge: The amount of water flowing past a point in a stream in a certain time.
gradient: How steep a stream or slope is.
velocity: How fast something moves and in what direction.
moraine: A ridge of rock and soil left behind by a glacier.
outwash: Sand and gravel carried and dropped by meltwater flowing from a glacier.
till: A mix of clay, sand, and rocks dropped directly by a melting glacier.
kettle: A hollow that forms where a block of glacier ice melts. It often fills with water to make a lake.
esker: A long, winding ridge of sand and gravel left by a stream that flowed under a glacier.

geologic record: The history of Earth stored in rock layers and fossils.
uniformitarianism: The idea that the same natural processes we see today also shaped Earth in the past.
relative age: Whether a rock or event is older or younger than another.
absolute age: The age of a rock or fossil in years.
superposition: In undisturbed rock layers, the oldest layer is at the bottom and the youngest is on top.
cryosphere: All the frozen water on Earth, such as glaciers, ice sheets, and sea ice.
index fossil: A fossil of a species that lived for a short time over a wide area. It helps date rock layers.
crosscutting relationships: A fault or intrusion is younger than the rock layers it cuts through.
radiometric dating: Finding the age of a rock by measuring how much of its radioactive elements has broken down.
ice core: A long tube of ice drilled from a glacier. Its layers record past climate.

Words from earlier grades that help with this unit.