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Biosphere: Definition & Explanation

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  • 0:00 Introduction
  • 0:27 What a Biosphere Isn't
  • 1:10 What a Biosphere Is
  • 2:03 Biospheres in the…
  • 2:46 Importance of Biospheres
  • 3:25 How Biospheres are Changing
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Lesson Transcript
Instructor: Jennifer Szymanski

Jen has taught biology and related fields to students from Kindergarten to University. She has a Master's Degree in Physiology.

All organisms, from the tiniest bacterium to the largest blue whale, need a place to live. The 'place on Earth's surface where life dwells' is called the biosphere. But what does this really mean? In this lesson, we'll look at the definition of the biosphere and examine how human activity is changing this important part of our planet.

Introduction

Life is everywhere - in the oceans, beneath the soil, and even inside your body. In 1875, geologist Eduard Suess was the first scientist to use the term biosphere to describe the part of the earth where life exists. Is the biosphere the same thing as a biome? And how do ecosystems fit into the picture? Let's start by looking at what the biosphere is not.

What the Biosphere Isn't

Because the earth is so big, there are almost limitless ways to study it. One of the simplest means by which science categorizes different aspects of the earth is by dividing it into 'spheres':

  • The lithosphere consists of the earth's crust and upper part of its mantle.
  • The atmosphere is what we call 'the air,' or the mixture of gases held around the earth by its gravitational pull.
  • The hydrosphere is the sum total of all of earth's water in any form, whether it's on the ground as liquid or ice, or in the clouds as water vapor.

All of these spheres interact with one another through many different means, such as the water cycle and biogeochemical cycles like the carbon and nitrogen cycles.

What the Biosphere Is

The biosphere is the fourth sphere, and consists of the places where life can be found. Since life exists in the air, on and in the earth, and on and in water, the biosphere overlaps, connects, and influences all of the other spheres - and they all affect the biosphere.

Considering the sheer number of organisms on earth, however, the biosphere is actually fairly small in size. Most of the biosphere's life is found between 500 meters below the surface of the ocean and six kilometers above the surface of the earth, although there are organisms, especially microorganisms, able to live at much higher and lower depths. The biosphere is quite old; its creation coincides with the appearance of the first bacteria, about 3.5 billion years ago. As life has changed and become more complex, so has the biosphere.

The Biosphere in the Hierarchy of Life

Where does the biosphere sit in the hierarchy of life? Since it encompasses all places where life exists, you might expect it to be near the top of the pyramid - and you'd be right:

Hierarchy of Life

Just beneath the biosphere on this pyramid are the biomes, or large communities of organisms defined by a particular climate. Below biomes in the hierarchy are ecosystems, which are usually defined as even narrower and more specialized populations of organisms that interact with non-living parts of the environment.

Importance of Biospheres

The study of the biosphere is the basis for ecology, the study of life and its interactions with the physical environment. For example, in the image here, red symbolizes high concentrations of algae and plant-like plankton in the oceans, while greens represent high numbers of land plants.

The biosphere as visualized based on the location of green plants and algae.
Global map of the biosphere based on primary producer location

Since plants are primary producers , that is, they are found at the bottom of food webs, they are good indicators of where other forms of life can be found. Ecologists monitor these types of data to try and predict what will happen to our environment. The information they obtain can help us to prepare for events that affect humans, like drought or severe storms.

How Biospheres are Changing?

Because the earth is always changing, the biosphere is always changing.

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