Our Changing Earth

• The Earth is made up of different kinds of materials, including rocks. Soil, water, and the gases of the atmosphere.

• Soils have different properties, including texture, the ability to hold water, and the ability to support life.

• A process is a series of events that lead to change. Different processes have helped shape Earth’s surface.

• Scientists are able to use tree growth rings and the layers of sedimentary rock to draw conclusions about Earth’s past.

Changing Earth’s Surface

• Processes that build up the Earth.– Lava flows– Sedimentation– Folding of the Earth’s crust

• Processes that wear down Earth’s surface land forms.– Weathering– Erosion– Earthquakes– Movement of glaciers

Earth’s Materials

• Rocks• Soils• Water• Gases• These materials are all natural resources.

Rocks

• Earth is made of rock.• Near the surface, rock is hard and dense. As you go

deeper into the Earth the temperature rises and the rock becomes molten.

• The outer layer of rock closest to Earth’s surface is the crust.

• A rock is any solid found in the Earth’s crust or below that is made of one or more minerals.

• Rocks are classified by color, size, shape, hardness, mineral crystals, and how the rock was formed.

Water

• Most of Earth’s surface is covered by water.• Most of this water is found in oceans and has salt and

other minerals dissolved in it.• Only 3% of the water is freshwater.• Some freshwater is frozen in ice caps and glaciers.• Groundwater is freshwater (such as rain) that collects

underground.• A small amount of freshwater is found in rivers, lakes,

and streams.

Soil

• Soil is essential to our existence.• Soil is necessary for growing crops to feed

humans and animals.• Soils stores nutrients and provides support for

plant roots and stems.

What is Soil?

• Soil is made up of the material left from rocks due to weathering and then…

• This material mixes with decaying plants and animals to make soil.

• It takes about 100 years to make 1 inch of soil.• Soil is classifies by texture, its own ability to hold

water, and its own ability to support life.

Types of Soil

• Most scientists rely on how much sand, silt, and clay there is in a soil in order to identify it.

• Soil texture is based on how large the pieces of clay and other particles in the soil are, as well as how much decayed plant and animal life there is (humus).

• Soil also has different chemicals that affect a soil’s ability to support life.

• Farmers and homeowners may add humus or special chemicals to aid in crop and plant growth.

The Gases of the Atmosphere

• Our Earth is surrounded by a blanket of air we call the atmosphere.

• This atmosphere reaches almost 350 miles above the surface of the Earth.

• Our atmosphere is a mixture of different gases.• The most common gas is nitrogen.• Humans and animals get oxygen from the atmosphere.• Plants take carbon dioxide from the atmosphere, which

they need for photosynthesis.

Why Do We Need the Atmosphere?

• Life on Earth is supported by the atmosphere.• The gases in the atmosphere absorb energy

from the sun.• It provides a moderate climate for us to live in.• It slows down meteors that might hit Earth.• It protects living things from the harmful effects

of the sun.

Forces Shaping the Earth’s Surface

Constructive Forces

• Folding to build mountains– When Earth’s crust is pushed together over millions of years, the

process can form mountains• Volcanoes and lava flows

– As molten rock comes through a hole in the Earth’s crust, the lava builds up on the ground around a volcano

– The Hawaiian Islands are the tops of volcanoes in the Pacific Ocean.– A lava flow leaves a smooth, flat, rock-hard surface.

• Sedimentation– Sedimentary rocks are made from pieces of sand, mud, and small

pieces of rock or shell that have been pressed together by weight above over time.

Destructive Forces• Weathering—the wearing down of rock by the actions of

wind, water, ice, and living things• Erosion—once a rock is broken down, erosion occurs

when wind, running water, ice, or gravity causes the particles to be moved to another location

• Glaciers—rivers of ice. Glaciers move slowly, scraping Earth’s surface, picking up loose rock, digging holes, wearing down mountains, and moving rocks and soil. Moving glaciers can carve out valleys.

• Earthquakes—movement in the Earth’s crust.An earthquake may tear down or build up. Lava may flow through cracks made by an earthquake.

Earth’s Past: Drawing Conclusions about “What Happened Before”

• People once believed the Earth was only a few thousand years old. In the 1830s, scientists concluded that it is much older than that.

• Scientists use many different ways to determine the age of the Earth– Tree-Growth Rings—each year, a tree adds a new layer of

wood to its trunk underneath the bark. Scientists can tell the age of the tree and also some things about weather conditions from the size of the rings.

– Sedimentary Rocks—Scientists use the layers in these rocks to determine the age of the rocks. They can also tell what type of environment existed when the rocks began forming.