A volcano erupts and sends ash high into the air. The ash spreads over a forest, blocking sunlight, and the trees grow more slowly that year. Which path do these interactions follow?

Loggers clear the trees from a steep hillside. The next storm washes soil down into the river, and the muddy water harms the fish. Which sphere's change started this chain?

Ocean water evaporates, wind carries the moisture inland, and rain later falls on a forest. Which two spheres interact first, before the water ever reaches the trees?

A glacier grinds across bedrock, and its meltwater carries the ground-up rock into a lake. Tiny plants living in the lake then grow faster. Which three spheres does this scenario involve?

Rain from the atmosphere gathers into a river. Over millions of years the river cuts a deep canyon through solid rock, and the sand it drops downstream gives streamside plants a place to take root. Which path do these interactions follow?

Tree roots grow into cracks in a boulder and slowly break it apart. Rain then soaks into the loose pieces, and grasses take root there. Which sphere does the biosphere act on first?

Strong winds lift desert dust and carry it far out over the ocean, where it settles into the water. Which sphere moved the dust, and which sphere received it?

Beavers build a dam across a stream. A pond forms behind it, and mud settles on the pond bottom, slowly changing the shape of the valley floor. Which sphere does the dam change first?

A town restores a wetland. Marsh plants slow the storm runoff, and mud settles out among their roots instead of reaching the river. Why does less mud reach the river?

Deep mountain snow melts each spring and fills the rivers that supply a city. After a warm, dry winter the snowpack is thin. Which sphere's change starts the chain that leads to the city's water shortage?

Rain falls from the sky and soaks into the ground. It is stored as groundwater in the spaces between grains of rock, and later the deep roots of a tree pull it up. Which three spheres does the water pass through, in order?

Dead leaves fall from trees into a stream. Decomposers break them down, and the tiny bits settle into the mud of the streambed. Which spheres does that matter pass through?

A class aims a fan at a tray of sand set beside a pan of water. The moving air lifts sand off the tray, and the sand lands in the water and settles on the bottom of the pan. Which three spheres does this model stand for?

During a two-week heat wave, scientists measured a shallow lake. The surface water warmed from 20 to 29 degrees Celsius, the oxygen in the water fell from 9 units to 5, and the fish crowded near a cool spring. Which three spheres does this link?

When farmers pump water out of an aquifer faster than rain can refill it, the ground above can slowly sink. This chain involves the biosphere, the hydrosphere, and the geosphere.

A rain-soaked landslide that buries a forest involves the atmosphere, the geosphere, and the biosphere.

A long drought dries the soil of a grassland. The bare ground blows into the air as dust, and the dust settles on a mountain snowfield far away, making the snow darker. Which path do these interactions follow?

Coral reefs off a coast are killed by unusually warm ocean water. Without the reef to break the waves, the beach behind it wears away faster each storm. Which three spheres does this scenario involve?

Bark beetles kill large patches of pine forest. The dead trees no longer take up water, so more rain runs off the slope and cuts gullies into the hillside. Which sphere's change started this chain?

Rain falls on a farm field, soaks through the soil picking up fertilizer, and drains into a bay where algae then grow thickly. Which three spheres does that fertilizer pass through, in order?