The History of Life On Earth

M&M Model for Radioactive Decay
or Half Life Lab

Make a timeline of life on Earth.

Section 12.1: How Did Life Begin?

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 they form?

One model that was suggested by Oparin and Haldane is called the primordial soup model. The gases from the volcanoes produced a chemical "soup." The chemicals reacted with one another, creating the amino acids of life. In 1953, Miller and Uray experimented with some gases and created the building blocks of life.

The Bubble Model, created by Louis Lerman in 1986, is a model explaining how some of those gases might have been available since there was no ozone layer yet to protect them from the damaging radiation of the sun.

clipart graphics

He felt that the gases might have come from underwater volcanoes and had been trapped in bubbles. 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.

Section 12.2: The Evolution of Cellular Life

cyanobacteria image from wikipedia

Among the first single celled organisms (prokaryotes) to appear were cyanobacteria. 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.

Two different groups of prokaryotes 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.

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.

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.

12.3: Life Invaded the Land

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.

Watch the video on natural selection below.

Do both of the labs on modeling natural selection that are in our text (in section 13.1 and at the very end of chapter 13.).

The video I had here was removed from youtube last night due to copy right violations. I'll get a replacement available asap. 2/17/12
1. Read the section in the book.
2. Answer the review questions.

Creepy Critters Classification Lab

Several Classification Activities

You'll find the next unit, on Ecology, at: Ecological Principles!

Homepage: Biology: Information, Videos, and Labs

Unit 1 on Cell Biology
Biology Labs, Activities, Videos, and Study Guides About Cells (Photosynthesis, Mitosis, Cell Organelles, and More)

Unit 2 on Genetics
Labs, Information, And Videos For High School Students Studying Genetics.

Unit 3 on The History of Life on Earth
The History Of Life On Earth.

Unit 4 on Ecology
Ecological Principles / Populations
Ecosystems
Biological Communities - Symbiosis, Niches, and Biomes
Global Changes And The Environment

Unit 5 on Diversity
An Introduction to Taxonomy - The Kingdoms and Domains Of Life
Learning About Viruses And Bacteria
Protists: Paramecium, Amoebas, Algae, Diatoms, Euglena, and Others
The Fungi Kingdom

Unit 6 on All About Plants
The Plant Kingdom

Unit 7 on The Animal Kingdom: Invertebrates
The Animal Kingdom - An Introduction
Sponges are Simple Animals
The Cnidarians: Jellyfish, Sea Anemones, Hydrozoans, and Corals
Earthworms, Christmas Tree Worms, Leeches, and Other Annelids
Mollusks Are Invertebrates

Check back later for additional biology units!

© 2012 Janiece Tobey. All rights reserved.
Page last updated 5/31/12.