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Evolution and the Beginnings of Life On Earth

How Did Life Evolve and Change Over Time?

The Earth as seen from the Apollo 17 spacecraft.

The Earth as seen from the Apollo 17 spacecraft.

How Did Life on Earth Begin?

What is the history of life on earth? How did life begin? What started the process? Is evolution real?

Do you ever wonder about these things?

The age of the earth, the origins of life, the primordial soup model and the bubble model, evolution and Charles Darwin's Natural Selection, fossils, and the classification of organisms are some of the topics we'll be covering in this article.

This page is designed to assist high schoolers studying biology. The sections of this page are organized to match the chapters in Unit 3 of Holt Biology: "Principles of Evolution," although this article can accompany any biology textbook, as well as stand alone. Each section of this article includes one or more youtubes, as I find that educational videos can enhance learning. Ideas for labs and hands-on activities are also included.

Biology students not using the Holt Biology text will likely still find this page to be of assistance in their study of evolution and the origins of life.

This unit has three chapters in it.

Chapter 12: History of Life On Earth.

Chapter 13: The Theory of Evolution.

Chapter 14: Classification of Organisms.

Holt Biology

Holt Biology

This is the Biology Text that members of our homeschoo-co-op are using. This article you are currently reading accompanies Holt Biology, adding additional photos, mneumonic devices, labs, and youtubes to what you learn in the text.

Although it's expensive if purchased new, you can purchase Holt Biology used for a significantly cheaper price at Amazon.

Usborne Encyclopedia of World History

The Usborne Internet-Linked Encyclopedia Of World History - a very helpful resource for our biology class!

This resource has many beautiful photos and interesting text! The first 100 pages or so includes information about the beginning of life on earth. For example one of the first spread of pages includes a colorful time line of life on earth. Other pages near the beginning of the book are about fossils, the birth of the earth, the changing world, the beginning of life, the first fish, the first animals to leave the oceans for the land, the Caroniferous swamps and insects, the age of amphibians, early reptiles, and many other topics. The beautiful photos increase the appeal of the book, as well as add interest and greater understanding.

As we go through the various sections on this page (and in our biology text), I'll recommend specific pages in the Usborne Encyclopedia of World History. If you have the World History book, take a few minutes and at least pour over the beautiful and informative pictures for that section.

The beginning of life on earth - Study guide of key terms and points

Scientists believe the earth was formed about 4.5 million years ago. It began as a fiery ball of rock. Volcanoes on the earth created huge clouds of steam and gas. As the steam cooled, it turned into water. It rained for thousands of years. Oceans formed. It’s believed by most scientists that life first formed in these oceans.

But how did the life form? Where did it come from?

One model of how life formed in the oceans was suggested by Oparin and Haldane. It is called the primordial soup model. The gases from the volcanoes produced a chemical “soup” in the oceans. The chemicals reacted with one another, activated by lightning, volcanic eruptions, and solar radiation, creating the amino acids of life.

In 1953, Miller and Uray decided to test the primordial soup model. They experimented with some gases - the same gases they felt existed on earth back when life was first beginning - and successfully created the building blocks of life.

Yet scientists now believe that the molecules that Miller and Uray used were not actually existing in abundance in the atmosphere when life on earth began. So where could the necessary chemicals have come from?

The Bubble Model, created by Louis Lerman in 1986, is a model explaining how some of those necessary, life-creating chemicals might have been available.

Louis Lerman felt that the gases might have come from underwater volcanoes and were trapped in underwater bubbles. The chemical reactions would have taken place quickly inside the bubbles because the chemicals would have been concentrated there. As the bubbles rose to the surface and then popped, the organic molecules were released into the air. Ultraviolet radiation and lightening supplied the energy for more chemical reactions. These now complex molecules then fell back into the ocean as it rained, beginning a new cycle.

The idea that life could have been formed from simple chemicals is sometimes referred to as spontaneous origin.

Radiometric Dating is the process of determining the approximate age of something by measuring how much of a certain radioactive isotope it still has. Radioisotopes give off energy in the form of radiation. The amount of time it takes for 1/2 of an amount of radioisotope to decay (break down and release energy) is called the half-life.

Small chains of amino acids can group together in tiny drops of water. These are called microspheres. Microspheres may have been the first step in the direction of cellular organization.

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Things to do for this section:

  1. Study the chart on pages 12 and 13 of the Usborne Internet Linked Encyclopedia of World History. It's an illustrated timeline of life on earth, beginning even before the first cells appeared.
  2. If you don't have the Internet Linked Encyclopedia of World History, you can view a timeline of the progression of life on earth on this National Geographic Website: Prehistoric Time Line.
  3. Read, "The Birth of the Earth" (pages 20 - 21) and "The Beginning of Life" (pages 24-25) in the Usborne Internet Linked Encyclopedia of World History.
  4. Visit and participate in the online activity of: Understanding Geologic Time
  5. Watch the youtube below.
  6. Short video of Miller–Urey experiment.
  7. Read section 12.1 in your Holt biology text.

Abiogenesis is a term which Mr. Anderson, in the video below, uses to mean "How life came to be through natural processes."


How Did Life Begin?



The Evolution of Cellular Life - Study Guide of Key Terms and Concepts

  1. Among the first single celled organisms (prokaryotes) to appear were cyanobacteria. Before cyanobacteria existed, there was not much oxygen on earth.The cyanobacteria carried out photosynthesis and released oxygen into the Earth’s oceans. The oxygen eventually escaped into the air. To the right you can see a photo of cyanobacteria.
  2. Two different groups of prokaryotes (single celled organisms) evolved early in the history of life on earth: Eubacteria and Archaebacteria. Eubacteria, such as e. coli, have the chemical peptidoglycan in their cell walls. Archaebacteria do not.
  3. Then about 150 billion years ago, the first eukaryotes showed up. Eukaryotic cells contain a nucleus and organelles (such as mitochrondria) enclosed in a membrane.

The theory of Lynn Margulis proposed in 1966 called endosymbiosis explains how mitochondria and chloroplasts became established in eukaryotic cells. According to the theory, bacteria entered large cells and began to live there. Eubacteria became mitochondria. Cyanobacteria became chloroplasts. There are quite a number of similarities which suggest the theory is true.

Scientists divide living organisms into 6 categories called kingdoms: Eubacteria, archaebacteria, protista, fungi, plants, and animals. Both Eubacteria and archaebacteris are single celled prokaryotes. Protists include both unicellular and multicelluar organisms. Fungi, plants, and animals all evolved later and are eukaryotes.

It is believed that most animals that are alive today originated during the late Precambrian and early Cambrian periods. This period is often called the "Cambrian explosion" due to the rapid diversification of animals going on during this period.

Many unusual marine animals lived during this time period as well. Fossils from the Burgess Shale geological formation in Canada have characteristics that are very different from the animals we have today. Take a look at the five-eyed Opabinia that lived during this time period. (Image is below.) Know any other five eyed creatures (that are real)?

About 440 million years ago, a mass extinction of organisms on earth took place. A mass extinction is when a large number of species become extinct in a short period of time. So far, we’ve had five mass extinctions, with the last one being during the time most of the dinosaurs became extinct. Some scientist say we are experiencing another mass extinction right now due the the destruction of the rain forests and the species that live there.

Five eyed Opabinia

Five eyed Opabinia

Things to read, watch, and do for this section.

1. Read "Shells and Skeletons" (pages 26 to 27), "The Crowded Seas" (pages 28 to 29), and "The First Fish" (pages 30 to 31) in the Usborne Encyclopedia of World History.

2. Have fun with this interactive website: Meet The Cambrian Critters.

3. Watch the youtube below.

4. Read section 12.2 in Holt Biology.

5. For additional information about the 6 kingdoms, visit: The Six Kingdoms. This site is full of colorful images, as well as information about the six kingdoms.

6. Here's a great image of The Emergence of Life On Earth

Life Invaded the Land - Study Guide of Key Terms and Concepts

Cyanobacteria began adding oxygen to Earth's atmosphere as they engaged in photosynthesis. The oxygen created the ozone layer in our atmosphere which blocks the damaging ultraviolet radiation of the sun, allowing more life to be able to inhabit the earth.

The first multicellular organisms on land were likely fungi living and cooperating together with plants or algae. These partnerships between fungi and the roots of plants are called Mycorrhizae. In these partnerships of mutualism, the plant gave nutrients to the fungus and the fungus gave minerals to the plant. Mutualism means both partners benefit from the relationship.

As plants covered the land, they provided a food source for land animals. The first animals to leave the ocean for life on land were the arthropods. Arthropods, such as crabs, lobsters, spiders, and insects have a hard outer skeleton, paired jointed limbs, and a segmented body. The biggest group of animals on earth is insects. There were the first animals to be able to fly.

Instead of having a hard outer skeleton like an arthropod, some animals have backbones. Animals with backbones are called vertebrates. The largest group of vertebrates are fish. (But remember that fish are only the largest group of vertebrates. Insects are the largest group of all animals, so there are more insects than fish.)

Amphibians, such as frogs, toads, and salamanders, are one type of vertebrate. They have smooth skin, four legs, and lungs for breathing on land.

Reptiles, like dinosaurs, snakes, lizards, crocodiles, and turtles are also vertebrates. They evolved from amphibians. They have a watertight skin which allows them to hold in more moisture. Although amphibians had to lay their eggs in water or in very moist places, reptiles were able to lay eggs on land because the shell of their eggs was watertight.

Birds and mammals, which are two other types of vertebrate animals, evolved from dinosaurs and reptiles.

Two factors which have influenced evolution are the mass extinctions and continental drift. Continental drift refers to how the continents have moved over time.

Things to read and watch for this section.

1. Watch the fascinating video that can be found on this website: Fish With Fingers. (Click the word, "view" to the right of the video.)

2. Read pages 32 to 42 on "Life on Land," "Fish Out of Water," "Swamps and Forests," "What Are Reptiles," "Early Reptiles," and "The Rise of the Reptiles" in the Usborne Encyclopedia of World History.