Gravity, Biosphere, Atmosphere, Hydrosphere, and Lithosphere Help

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


If the Earth is spinning, then what force keeps us and everything else in place? Gravity .

In 1666, English scientist, Sir Isaac Newton (the guy who had an apple fall off a tree and land on his head) said the objects on a spinning Earth must be affected by centrifugal force. He thought the objects on the Earth would fly off unless there was a stronger force holding them on. This line of thinking led Newton to come up with the Universal Law of Gravitational Attraction .

Newton described the law in the following mathematical way:

Planet Earth

where F is the force of gravitational attraction, M 1 and M 2 are the masses of two attracting bodies, and d is the distance between the center of M 1 and the center of M 2 . The larger M 1 and M 2 are, and the smaller d is, then the greater the F (force of attraction) will be. So, since the Earth is huge compared to a horse or a human or volleyball, the force of attraction to the Earth is huge. When planets are heavy and close together, they will be attracted to each other!

Newton also realized that since gravity pulls all objects toward the Earth’s center (known as a radial force ), the centrifugal force (the force of the object pulling away as it spins) is greater the farther away the object from the axis of spin. In other words, the centrifugal force is greatest at the equator and less at the poles. The interaction of the two forces causes the Earth to be flatter at the poles and a bit wider at the waistline (equator). This is measured at the Earth’s radius as 6357 km at the poles, but bulges at the equator to 6378 km. The Earth is so big though that it still looks like a perfect sphere from space.


All of life on the Earth is contained in the biosphere . All the plants and animals of the Earth live in this layer which is measured from the ocean floor to the top of the atmosphere. It includes all living things, large and small, grouped into species or separate types. The main compounds that make up the biosphere contain carbon, hydrogen, and oxygen. These elements interact with other Earth systems.

The biosphere includes the hydrosphere, crust, and atmosphere. It is located above the deeper layers of the Earth.

Life is found in many hostile environments on this planet, from extremely hot temperatures near volcanic spouts rising from the ocean floor to polar subzero extremely cold temperatures. The Earth’s biodiversity is truly amazing. Everything from exotic and fearsome deep-ocean creatures to sightless fish found in underground caverns and lakes are part of the biosphere. There are sulfur-fixing bacteria that thrive in sulfur-rich, boiling geothermal pools, and there are frogs that dry out and remain barely alive in desert soils until infrequent rains bring them back to life. It makes the study of Earth Science fascinating to people of many cultures, geographies, and interests.

However, the large majority of biosphere organisms that grow, reproduce, and die are found in a narrower range. The majority of the Earth’s species live in a thin section of the total biosphere. This section is found at temperatures above zero, a good part of the year, and upper ocean depths to which sunlight is able to penetrate.

The vertical section that contains the biosphere is roughly 20,000 m high. The section most populated with living species is only a fraction of that. It includes a section measured from just below the ocean’s surface to about 1000 m above it. Most living plants and animals live in this narrow layer of the biosphere. Figure 1-5 gives an idea of the size of the biosphere.

Planet Earth

Fig. 1-5. Life exists in a very narrow range.

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