Graph a triangle (STU) and reflect it over the y-axis to create triangle S′T′U′.
Biology Notebook: Earth’s Early Atmosphere
Page 1: Origin of Life on Earth
What makes Earth an ideal home for its diverse inhabitants?
- Earth makes an ideal home for its diverse inhabitants because it has liquid water, an optimal distance from the sun, and an atmosphere that contains a mix of important elements and molecules.
Key Terms: Jot down terms and definitions that are new to you. You will see them used in the lesson.
Page 2: The Early Earth
What was Earth’s early atmosphere made of?
- Earth’s early atmosphere is made of primarily of carbon dioxide, water vapor, and nitrogen.
Compare and contrast early Earth and modern Earth.
- Early earth had low oxygen, UV radiation, high heat, not a lot of water. Modern earth has lots of oxygen, low UV radiation, abundant amount of water, ozone layer.
What are organic molecules?
-Organic molecules are carbon-based molecule.
Why are scientists interested in the origin of organic molecules?
- Scientists are interested in the origin of organic molecules because it is important to life on earth.
What are two examples of organic molecules that scientists think first formed?
-Two examples of organic molecules that scientists think first formed is amino acids and nucleotides.
Why are the reactions that occurred in early earth different from modern Earth?
- Scientists argued that the reason we do not observe these reactions occurring today is the atmosphere now has a greater amount of oxygen gas. Oxygen interferes with the reactions that would form carbon-based organic molecules.
Page 3: Chemical Experiments
What hypothesis did Miller and Urey want to test?
- The hypothesis Miller and Urey wanted to test is the conditions of early Earth favored chemical reactions that were able to build small organic molecules from inorganic molecules in the atmosphere.
What did their experiment produce?
- Amino acids and other small organic molecules could have formed spontaneously in Earth's early atmosphere.
What did they add to make it like Earth’s early atmosphere?
- They added methane, ammonia, and hydrogen gases to the water vapor.
Where did they think that the energy came from to cause this process to occur?
-They thought that the energy came from to cause this process to occur is lightning and the intense radiation that penetrated the thin primitive atmosphere provided the energy needed for these reactions.
What was formed based on the results of the experiment?
- Their experiment produced a variety of amino acids and other small organic molecules.
Page 4: Chemical Evolution
What is another way that organic molecules might have arrived on Earth?
- Organic molecules arrived on the early Earth on meteorites and comets from space.
How did large organic molecules form without the presence of enzymes?
- Scientists have observed that chemical bonds sometimes form between small organic compounds on hot surfaces. Scientists speculate that ocean water containing small organic molecules, like those formed in the Miller-Urey experiment, splashed onto hot sand, clay, or rock. As the water evaporated on the hot surface, the small organic compounds could have bonded together. Although they have not been able to build large protein molecules in this way, scientists have been able to form smaller chains of amino acids using this method.
What do all living organisms contain?
- All living organisms contain genetic information.
Explain the RNA world hypothesis. (Be sure to explain the significance of both DNA and RNA)
- RNA world hypothesis is that some of the first large organic molecules to form and self-replicate were RNA molecules, with DNA molecules forming much later.
Define catalyst.
- Catalyst is a substance the rate of reaction without undergoing any permanent chemical change.
Explain what helps RNA catalyze.
- One important reaction that RNA helps to catalyze is the building of new RNA molecules.
Page 5: Early Cells
Describe the earliest cells.
- These early single-celled organisms were prokaryotes, a small simple type of cell that lacks a true nucleus.
Did the first prokaryotic cells need oxygen?
- The first prokaryotic cells lived on an Earth that had little to no oxygen in its atmosphere.
How did the first prokaryotic cells obtain energy?
- These cells were heterotrophs that had to obtain their energy by taking in nutrients as food.
Define heterotroph.
- Heterotroph is organisms that must eat or consume other organisms, plants, animals, or both, to get their energy.
What did the early cells have as a food source?
- Scientists speculate that their food was the rich assortment of organic molecules thought to be present in the ocean water at that time.
List the four types of cells found today those scientists believe are like the early cells on Earth and one interesting fact about each.
- 1. the presence of small organic molecules (through spontaneous synthesis or from meteorites) 2. assembly of these molecules into larger organic molecules/polymers (such as RNA and protein) 3. RNA molecules becoming self-replicating 4. the packaging of groups of molecules into microspheres that can maintain an internal chemistry different from surroundings
What does fossil evidence show us about the earliest and most abundant autotrophic cells?
- Fossil evidence shows that the earliest and most abundant autotrophic cells were ancestors of modern-day cyanobacteria.
What are cyanobacteria and why are they important?
- Are photosynthetic prokaryotes that live in the water. Even though these bacteria cells are very small, they often grow together in large colonies that can be seen with the naked eye. Cyanobacteria can be found in almost every conceivable environment, from oceans to fresh water to moist soil. These photosynthetic cells are essential to ocean ecosystems, serving as the autotrophs at the base of many marine food chains.
As cyanobacteria and other autotrophs increased, how did the atmosphere change?
- The atmosphere change by the amount of oxygen in the atmosphere increasing.
What became the dominant life forms on the planet as the oxygen became more abundant?
- The dominant life forms on the planet as the oxygen became more abundant is aerobic autotrophs and heterotrophs.
Page 6: Formation of Microspheres
What is a microsphere?
- Microsphere is groups of molecules; tiny bubbles filled with groups of large organic molecules.
Microspheres are not cells, but they do have similar characteristics. Identify the characteristics of microspheres.
- 1. These bundles of molecules can maintain an internal environment different from the surroundings outside the bubble. 2. They also have a simple way of storing and releasing energy.
How do microspheres grow and what happens when it reaches an unstable size?
- Microspheres grow and when it reaches an unstable size they split into smaller microspheres.
How does the hypothesis of microspheres build on the RNA world hypothesis?
- If RNA molecules could self-replicate, it would mean that whenever a microsphere split, the early genetic coding in the RNA would pass to the newly formed microspheres.
Practice question:
If there was not an increase in cyanobacteria in early Earth, what would have happened to Earth’s early atmosphere?
The amount of oxygen would have increased, causing an increase in aerobic autotrophs and heterotrophs
The amount of oxygen would have increased, causing a decrease in aerobic autotrophs and heterotrophs.
The amount of oxygen would have decreased, causing an increase in aerobic autotrophs and heterotrophs.
The amount of oxygen would have decreased, causing a decrease in aerobic autotrophs and heterotrophs.
Which best describes the atmosphere of the early Earth?
Little or no oxygen, mostly carbon dioxide, water vapor, and nitrogen
Little or no carbon dioxide, mostly oxygen, water vapor, and nitrogen
Little or no water vapor, mostly oxygen and carbon dioxide, with some nitrogen
Large amounts of hydrogen cyanide with low amounts of carbon dioxide and oxygen
