Chapter 19 History of Life on Earth
Opening Activity Draw a picture of what you think Earth s first life form may have looked like and label the parts of the organism.
Content Objectives I will be able to identify: What did the Miller-Urey experiment showed about the formation of the basic molecules of life. The two theories that propose where the building blocks of life originated in early Earth. How molecules have become packaged into cells that contain inheritable cellular instructions.
Chapter 19 Section 1: How Did Life Begin Key Vocabulary Terms
Microsphere A hollow microscopic spherical structure that is composed of a polymer
Ribozyme A type of RNA that can act as an enzyme
Chapter 19 Section 1: How Did Life Begin Notes
Chapter 19 Section 1: How Did Life Begin The Basic Chemicals of Life
The Basic Chemicals of Life In the 1920s, scientists Aleksandr I. Oparin and John B. S. Haldane suggested that Earth s early oceans contained large amounts of organic molecules.
The Basic Chemicals of Life They proposed these molecules formed spontaneously in chemical reactions that were activated by energy from the sun, volcanic eruptions, and lightning.
The Basic Chemicals of Life Oparin and other scientists hypothesized that the early atmosphere was rich in hydrogen gas (H 2 ) and hydrogen-containing gases, such as water vapor (H 2 O), ammonia (NH 3 ), and methane (CH 4 ).
The Basic Chemicals of Life They thought that if the atmosphere lacked oxygen, a variety of organic compounds made up of these elements could form.
The Basic Chemicals of Life The hypothesis was tested in the 1950s by American scientists Harold Urey and Stanley Miller.
The Basic Chemicals of Life Miller and Urey confirmed that organic compounds could form from inorganic molecules given certain conditions.
Miller-Urey Experiment
The Miller-Urey Experiment In this experiment, Miller placed hydrogencontaining gases into a device.
The Miller-Urey Experiment He used electrical sparks to simulate lightning.
The Miller-Urey Experiment After a few days, Miller found organic molecules in his device, including some of life s basic building blocks: amino acids, fatty acids, and other hydrocarbons (molecules made of carbon and hydrogen).
The Miller-Urey Experiment The Miller-Urey experiment showed that, under certain conditions, organic molecules could form from inorganic molecules.
The Miller-Urey Experiment We now know that the molecules used in Miller s experiment could not have existed in abundance on early Earth.
The Miller-Urey Experiment Four billion years ago, shortly after it formed, Earth did not have a protective ozone layer.
The Miller-Urey Experiment Ultraviolet radiation from the sun would have destroyed any methane and ammonia in the atmosphere.
The Miller-Urey Experiment When ammonia and methane gases were absent from the Miller-Urey experiment, key biological molecules were not made.
The Miller-Urey Experiment However, the experiment shows that complex biological compounds can form from simple building blocks.
Think, Share, Write #1 What compounds were formed in the Miller-Urey experiments?
Think, Share, Write #1 What compounds were formed in the Miller-Urey experiments? Simple organic compounds, such as amino acids, fatty acids, and other hydrocarbons were formed in the Miller-Urey experiments.
Chapter 19 Section 1: How Did Life Begin Life s Building Blocks
Life s Building Blocks Two Hypotheses Hydrothermal Vents. Meteorites.
YOUR TURN Active Reading Section 1 How Did Life Begin?
Hydrothermal Vents One hypothesis that addresses the origin of life states that early biological molecules formed close to hydrothermal vents.
Life s Building Blocks, continued Some meteorites contain amino acids. Such molecules could have arrived on early Earth, when frequent meteorite impacts were common.
Chapter 19 Section 1: How Did Life Begin The First Cells
The First Cells Research continues to discover how biological molecules grouped together to form cells.
The First Cells Scientists must figure out how amino acids first linked together to form proteins.
Forming a Cell Scientists have conducted research to determine how molecules became packaged together inside a cell membrane.
Forming a Cell When studying the behavior of organic molecules in water, scientists have observed that lipids tend to combine in water.
Forming a Cell Certain lipids, when combined with other molecules, can form a tiny droplet that has a surface that resembles a cell membrane.
Further research has shown that short chains of amino acids can form tiny spherical structures called microspheres. Forming a Cell
Many scientists think that the formation of microspheres may have been the first step toward cellular organization. Forming a Cell
Forming a Cell Microspheres could not be considered cells unless they had the characteristic of heredity.
Origins of Heredity Scientists have studied the origins of heredity by studying the formation of proteins.
Origins of Heredity In the laboratory, scientists have not been able to make proteins or DNA form spontaneously in water.
Origins of Heredity They have been able to form short chains of RNA, the nucleic acid that helps to carry out the instructions of DNA.
Origins of Heredity RNA molecules may have been the first self-replicating molecule.
In the 1980s, American scientists Thomas Cech and Sidney Altman found a certain type of RNA molecule, called a ribozyme, that can act like an enzyme. Origins of Heredity
Origins of Heredity They also showed that RNA can form spontaneously in water, without DNA.
Origins of Heredity They hypothesized that RNA was the first self-replicating molecule that stored information and catalyzed the formation of the first proteins.
One idea of how RNA could have been involved in protein synthesis is shown here.
Origins of Heredity Cech and Altman further hypothesized that RNA could have changed evolved from one generation to the next.
Origins of Heredity Scientists hypothesize that DNA and proteins eventually took over these roles in the cell.
Think, Share, Write #2 Explain how RNA could have existed before DNA.
Think, Share, Write #2 Explain how RNA could have existed before DNA. RNA can form spontaneously in water, and DNA cannot. RNA can also perform many functions that DNA performs in cells.
The Miller-Urey experiment showed that, under certain circumstances, organic compounds could form from inorganic molecules. Summary
Summary Among the scientific theories that address the origin of life, one suggests that life began close to hydrothermal vents, and another proposes that organic molecules arrived on early Earth from a meteorite.
Summary The formation of microspheres might have been the first step toward cellular organization.