Gravity, Biosphere, Atmosphere, Hydrosphere, and Lithosphere Help (page 2)

By — McGraw-Hill Professional
Updated on Aug 30, 2011


The atmosphere of the Earth is the key to life development on this planet. Other planets in our solar system either have hydrogen, methane, and ammonia atmospheres (Jupiter, Saturn), a carbon dioxide and nitrogen atmosphere (Venus, Mars), or no atmosphere at all (Mercury).

The atmosphere of the Earth, belched out from prehistoric volcanoes, extends nearly 563 kilometers (350 miles out) from the solid surface of the Earth. It is made up of a mixture of different gases that combine to allow life to exist on the planet. In the lower atmosphere, nitrogen is found in the greatest amounts, 78%, followed by oxygen at 21%. Carbon dioxide, vital to the growth of plants, is present in trace levels of atmospheric gases along with argon and a sprinkling of neon and other minor gases. Figure 1-6 shows the big differences between the amounts of gases present.

Planet Earth

Fig. 1-6. The Earth’s atmosphere is made up of various gases.

Oxygen, critical to human life, developed as microscopic plants and algae began using carbon dioxide in photosynthesis to make food. From that process, oxygen is an important by-product.

The mixture of gases we call, air, penetrates the ground and most openings in the Earth not already filled with water. The atmosphere is the most active of the different “spheres.” It presents an ever changing personality all across the world. Just watch the nightly weather report in your own area to see what I mean. In fact, you can see what the weather is doing around the world by visiting the following websites:


The global ocean, the Earth’s most noticeable feature from space, makes up the largest single part the planet’s total covering. The Pacific Ocean, the largest of Earth’s oceans, is so big that all the landmass of all the continents could be fit into it. The combined water of the oceans makes up nearly 97% of the Earth’s water. These oceans are much deeper on average than the Earth is high. This large mass of water is part of the hydrosphere .

The hydrosphere describes the ever changing total water cycle that is part of the closed environment of the Earth.

The hydrosphere is never still. It includes the evaporation of oceans to the atmosphere, raining back on the land, flowing to streams and rivers, and finally flowing back to the oceans. The hydrosphere also includes the water from underground aquifers, lakes, and streams.

The cryosphere is a subset of the hydrosphere. It includes all the Earth’s frozen water found in colder latitudes and higher elevations in the form of snow and ice. At the poles, continental ice sheets and glaciers cover vast wilderness areas of barren rock with hardly any plant life. Antarctica makes up a continent two times the size of Australia and contains the world’s largest ice sheet.


The crust and the very top part of the mantle are known as the lithosphere ( lithos is Greek for “stone”). This layer of the crust is rigid and brittle acting as an insulator over the mantle layers below. It is the coolest of all the Earth’s layers and thought to float or glide over the layers beneath it. Table 1-1 lists the amounts of different elements in the Earth’s crust.

The lithosphere is about 65–100 km thick and covers the entire Earth.

Scientists have determined that around 250 million years ago, all the landmass was in one big chunk or continent. They named the solid land, Pangea that means “all earth.” The huge surrounding ocean was called Panthalassa that means “all seas.” But that wasn’t the end of the story, things kept changing. About 50 million years later, hot interior magma broke through Pangea and formed two continents, Gondwana (the continents of Africa, South America, India, Australia, New Zealand, and Antarctica) and Laurasia (Eurasia, North America, and Greenland). Scientists are still trying to figure out why the super continents split up, but “hot spots” in the Earth’s mantle seem to help things along.

Table 1-1 The variety of elements in the Earth’s crust make it unique.

Elements of the Earth’s crust





















By nearly 65 million years ago, things had broken apart even more to form the continental shapes we know and love today, separated by water.

Practice problems of this concept can be found at: Planet Earth Practice Test

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