How North America Almost Separated Into Two Pieces

What is the Midcontinent Rift?

• A mountain range

• A deep ocean trench

• A huge scar across the land

• A volcanic island chain

What causes slight variations in the strength of gravity from place to place on Earth?

• The amount of water in the soil

• The density of rocks beneath the surface

• The height of mountains

• The speed of Earth's rotation

How are flood basalts formed?

• When glaciers melt and deposit sediment

• When massive amounts of magma erupt from the Earth's mantle

• When tectonic plates slide past each other

• When rivers carry sediment to the ocean

What is the first step in the Wilson Cycle when a continent begins to break apart?

• A subduction zone forms

• Continents collide to form mountains

• A rift forms and hot material rises from the mantle

• New seafloor is created at a mid-ocean ridge

What happened when the continent Amazonia broke away from Laurentia?

• It caused a new supercontinent to form.

• It pulled and stretched Laurentia from the side.

• It immediately created a new ocean.

• It caused the Grenville orogeny.

What is 'passive rifting'?

• When a hot plume from the Earth's mantle rises and melts the crust.

• When two continents collide, forming mountain ranges.

• When a sideways force pulls a continent apart.

• When glaciers erode the surface of the Earth.

What causes 'active rifting' in the Earth's crust?

• A sideways force pulling the continent apart.

• A hot plume from the mantle rising, heating, and melting the crust.

• The collision of two tectonic plates.

• The erosion of rocks by rivers and glaciers.

What is a unique characteristic of the Mid-continent Rift compared to other rifts?

• It formed the deepest ocean on Earth.

• It is the deepest known rift on Earth that did not form an ocean.

• It was caused by a collision with another landmass.

• It is still actively spreading today.