LIFE'S BIG QUESTIONS: Where Did Life Come From?
Scientists have long questioned where and when life emerged on our planet. Alan Alda joins biologists Norman Pace and Sue Barns as they search for answers in the boiling hot springs of Yellowstone. The discovery that microscopic creatures can survive in these extreme conditions, along with DNA analysis, suggests that these organisms may be similar to the earliest life-forms on Earth. (Note: Organisms in the spring are not true bacteria, but a group of living creatures discovered only recently.)
Activity 1: Just How Tough Are Bacteria?
Activity 2: Volcanic Calderas
phases of matter
ACTIVITY 1: Just How Tough Are Bacteria?
Many scientists believe that the earliest forms of life existed all over primitive Earth in conditions very similar to the ones you saw in the Yellowstone hot springs. If life can exist at high temperatures, then is it possible that simple, modern terrestrial bacteria might have inherited some of the traits associated with the more ancient forms? Let's find out.
- small pot
- hot plate
- carrot slice
- petri dish or sterile jar
- filter paper
- grease pencil
- paper towels
- insulated glove
NOTE: WEAR YOUR EYE AND CLOTHES PROTECTION. ALWAYS USE A POT HOLDER OR INSULATED GLOVE TO HANDLE HOT EQUIPMENT.
- Cut a piece of carrot about 5 cm long, 2 cm wide and no more than 5 cm thick. Fill a small pot with enough clean water to boil the carrot.
- Using a hot plate, boil the carrot in water for 10 minutes.
- While the carrot boils, sterilize the petri dish, filter paper and forceps in boiling water or a steam bath.
- Place filter paper on the bottom of the petri dish.
- Place the boiled carrot flat side down on the filter paper. Cover the dish and label it. Place the dish in a warm place. Let it sit undisturbed 3 to 4 days.
- Write your observations each day in a journal.
- After a few days, examine the carrot under a microscope for growth samples. Draw observations in your journal.
Note: This experiment can be done in a mason jar, but it's important to prepare a sterile sample, no matter where this experiment is conducted. Not all carrot samples will produce bacterial growth. As in all scientific processes, conclusions are open to discussion.
- Define the term endospore.
- Were all the bacteria on the carrot killed by boiling?
- If bacteria do appear on carrot samples, where do they come from? (Endospores in carrot.) Could this bacteria have inherited traits found in ancient bacteria? What is the difference between an inherited and an acquired trait?
- Research microscopic life-forms that survive in the deep ocean near hydrothermal vents. Are these creatures similar to the descriptions of the earliest life-forms?
- Speculate on what might have happened if Earth had never cooled down. Write a description of the types of life forms that may have evolved. Support your claim with explanations consistent with present-day knowledge about evolution.
- Why does the water in the hot springs "boil" at less than 212 degrees F? (Reduced air pressure at this elevation reduces the boiling point of water.)
ACTIVITY 2: VOLCANIC CALDERAS
Much of Yellowstone Park lies inside a caldera, a collapsed volcano that erupted about 800,000 years ago. A caldera forms when the crater of a volcano collapses or explodes. Magma close to the surface exerts upward pressure on a volcano and leaks out in the form of lava. If the leak becomes plugged, water can drain into the pressure-laden magma, causing a buildup of tremendous steam pressure under the volcano. If the pressure becomes too great, the volcano explodes. If the pressure gradually lessens, the top of the volcano subsides and collapses. In either case, a caldera is formed. The "blowout" causes the crater to expand to a diameter as small as a mile or in the case of the larger Yellowstone caldera, 40 miles wide!
In this activity, you can demonstrate how a caldera is formed.
- small balloon
- 2 - 3 feet of plastic tubing
- tubing clamp
- large cardboard box
- dissecting pin or other long pin
- Choose a piece of plastic or rubber tubing wide enough that the balloon opening must stretch to cover its end.
- Fold a sheet of newspaper to conform to the bottom of the cardboard box. Make a hole slightly larger than the plastic tube in the center of the bottom of the box. Thread the tube through the hole, leaving the balloon inside the box. Inflate the balloon by blowing through the tube. Clamp the tube.
- Slowly pour sand over the balloon until it is completely covered. Fashion a small crater in the top of the sand mound. Measure the angle formed by the slope of your "volcano."
- Slowly release the air in the balloon while observing the "crater."
- Remove the sand, inflate the balloon and repeat step 3, but this time insert a long pin carefully through the bottom of the box to pop the balloon.
CAUTION: DO NOT TRY TO OBSERVE THE REACTION FROM THE TOP OF THE BOX. VIDEOTAPE OR FILM IT AND REPLAY IT IN SLOW MOTION (OR WATCH IT ON A MIRROR).
- Compare the angle formed by the slope of your volcano to the physical characteristics of the three types of volcanoes. Which type does your model represent?
- Do you observe any difference between the gently subsided caldera and the exploded one?
- What geologic processes do the experiments model?
(Subsidence, such as sinkhole formation, caldera formation, and to some degree, meteor cratering.)
- What does the balloon represent?
- What does the air in the balloon represent?
(Air represents gas or steam in the magma.)
- What would happen if you wet the sand mountain before collapsing it?
- Yellowstone Park rangers tell a story of a man who jumped into a hot spring to rescue his dog. The spring had a pH of 3 and a temperature approximately 190 degrees F. What do you think happened to the man? Why?
(The man survived, but his dog did not. The high temperature caused severe third degree burns. The acid pH exacerbated the burns.)
- Some of the hot springs in Yellowstone have a strong smell of rotten eggs. Their waters are acidic. What kind of acid would you expect to find in a "smelly" hot spring? What kind of acid, if any, would you expect to find in a "non-smelly" hot spring?
(A combination of hydrogen sulfide and sulfur dioxide causes the rotten egg smell, so the acid must be sulphuric. The non-smelly springs contain dissolved carbon dioxide from the breakdown of limestone, so the acid would be carbonic.)
- A mining company has proposed building a mine three miles from the border of Yellowstone National Park -- an area still considered volcanically active. What are the pros and cons of the project? What might be the impact on the park's water and wildlife? What about the rights of the company that owns the land? Find out the status of this project, recently debated by Congress and the Department of the Interior. What do you think?
Scientific American Frontiers
Fall 1990 to Spring 2000
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