Category: Backgrounds

Erosion – Background

The landscape around us is a patchwork of mountains and valleys, steep cliffs and gentle slopes, lakes, ponds, and puddles, stitched together with a network of rivers and streams. The features of our landscape tell a story about the process of erosion, in which landforms are worn away and their fragments carried off to another place. Jagged mountains became rolling hills, flat plains became deep river gorges, steep bluffs crumble into the sea.

Erosion is the process by which rocks and sediments are loosened and moved to different places on the Earth’s surface, where they may be deposited and become parts of other landforms, or buried to eventually become solid rock again. The agents of erosion – wind, water, ice, and gravity – are powerful forces constantly at work shaping and reshaping the land. Continue reading Erosion – Background

Rocks and Minerals – Background

Who hasn’t stopped to pick up a pebble, to admire or wonder about its color or texture, or just to toss it in your hand? Rocks speak to us, especially as children, and for some people, like geologists, sculptors, stone masons, and rock hounds, the fascination with rocks lasts a lifetime. Of course rocks can’t really talk, but they can tell us about the history of our rocky planet and its living creatures, if we know where and how to look.

Every pebble we find is part of the geosphere, the rocky covering of our planet. The Earth’s crust is a layer of rock from three to thirty miles thick that underlies Continue reading Rocks and Minerals – Background

Blanket of Air – Background

The Earth’s atmosphere, the layer of air that surrounds the planet, is a protective blanket that shields us from harmful radiation and traps heat energy, storing warmth from the sun and keeping temperatures in a range that makes life possible. Animals need air to breathe, plants need it for photosynthesis, and living things also use air to fly, carry scents and sounds, and keep warm. With its many functions in our lives, it’s worthwhile exploring the nature of air.

Held in place by Earth’s gravity, the atmosphere is an envelope of air that extends outward from the surface for some 500 miles, becoming thinner and sparser with distance. Dry air is composed primarily of three gases, with nitrogen making up 78%, oxygen 21%, and argon just under 1%. The remainder is made up of other gases, such as carbon dioxide, ozone, helium, and hydrogen. Continue reading Blanket of Air – Background

Nature of Sound – Background

If a tree falls in the forest, a bird sings, or a beaver slaps its tail, does it make a sound if no one is there to hear it? To think about this riddle, we need to understand the nature of sound – what it is and how we perceive it. Sound is important in our lives and the lives of other animals. Our sense of hearing helps us learn about and monitor our surroundings. And for animals that chirp, croak, bark, or talk, sound provides a highly effective means of communication.

Sound is what we hear when something is vibrating. Pluck a rubber band or a guitar string, and we hear a sound. How does the sound reach our ears? As the string vibrates, oscillating rapidly back and forth, it pushes or compresses the air Continue reading Nature of Sound – Background

Water – Background

From ice crystals to raindrops, water in its many forms is a remarkable substance that is essential to all living things. Most organisms are made largely of water, many also live in or on the water, and all require water to survive. The Earth’s water is a finite resource but one that is constantly on the move. As it cycles from the Earth’s surface to the atmosphere and back, it changes form. Water evaporates into vapor, condenses into droplets, and precipitates as rain or snow. Much of the water that falls on land is transported back to the air by plants, a process that is only possible because of water’s unique properties.

The Earth’s water was formed billions of years ago as the planet itself was forming, though there is still much to learn about how this came about. Water is Continue reading Water – Background

Wind and Clouds Aloft – Background

Watching the sky can be peaceful or exciting, depending on the day or hour. Sometimes the sky is as still as a painting with snow-white clouds on a deep blue canvas. At other times ragged clouds race across the sky, propelled by high winds aloft. Sky-watching may take us on flights of fancy or lead us to ponder why the wind blows, or how clouds take such different shapes, or what wind and clouds can tell us about the weather.

Winds, or flowing air currents, are caused by warm air rising and cool air flowing in to take its place. Because the sun heats the Earth unequally, the atmosphere is heated unequally too, warming and rising in some parts, cooling and sinking in others. This creates areas of low pressure, where the air has Continue reading Wind and Clouds Aloft – Background

Get Your Bearings – Background

Animals are always on the move, traveling from place to place to look for mates, find food, tend their young, or migrate to and from a faraway winter home. To do so, animals must have a sense of where they are and a way to navigate between destinations. Many aspects of the physical world provide important cues for animals on the go, some that we can sense and others that are outside our range of perception. What environmental cues do animals use to get their bearings, and how do people find their way?

From an early age, we begin to develop a sense of direction, an understanding of where we are inside our homes, which soon expands to school and beyond. One of the ways we orient is by forming a mental map of familiar places – a picture in Continue reading Get Your Bearings – Background

Spiders: Web-Builders and Wanderers – Background

Hanging under eaves, tucked in the cracks on tree bark, hidden in tall grass, spiders and webs can be found nearly everywhere you look in late summer. Not all spiders spin webs, however. Some actively hunt for prey, scurrying over dirt in the garden or ambushing pollinators visiting flowers. Whether wanderers or web weavers, spiders abound in nearly every habitat on Earth, with estimates of one million individuals living in each acre of grassy field. There are about 2,500 spider species in North America, all different and each well adapted to its role as a small but effective predator.

Spiders are arthropods, which means that they have jointed legs and hard exoskeletons, as insects do. Continue reading Spiders: Web-Builders and Wanderers – Background

Tremendous Trees – Background

Towering above us, branches reaching to the sky, trees are a familiar feature of the landscape, whether a forested hillside, a busy city park, or our own backyard. In the summer, trees form a green canopy shading and cooling the ground below. In winter, they stand silently braced against the cold and snow. With some 100,000 different species worldwide, trees come in a variety of shapes and sizes and thrive in a wide range of habitats. But what makes a tree a tree?

By definition, trees are large, woody, perennial plants. From underground roots to leafy branches, each part plays an important role in the survival of the tree. Continue reading Tremendous Trees – Background

Grasses and Grains – Background

Compared with lacy ferns, showy flowers, and towering trees, the grasses seem hardly worth noticing. Yet these modest plants flourish in harsh conditions, cover much of the land masses of the world, support huge populations of grazing animals, and produce prodigious amounts of seeds – the grains that feed our livestock and us. Grasses have fascinating and unique adaptations that make them extremely resilient and set them apart from other kinds of plants.

Grasses grow just about anywhere – in fields, wetlands, saltmarshes, mountaintops, deserts, and even in shady forests. There are ten thousand species worldwide, and – in prairies, savannahs, pampas, and steppes – they cover a quarter of the earth’s land. Grasses dominate in conditions that are challenging for most other plants. They thrive in open plains that are dry and windy, lacking in shade, exposed to rain and snow, blizzards, and tornados. They are also built to survive fire and grazing by hordes of animals, from swarms of insects to herds of elephants. Continue reading Grasses and Grains – Background