A teacher is introducing the geologic time scale to third-grade students. She tells them that the entire history of Earth, from its formation to the present day, was 24 hours long, with 12:00 midnight representing the time of the formation of Earth and 12:00 midnight the following night representing the present day. About what time did humans appear in this 24-hour time scale?
- A. 11:58 PM
- B. 9:00 PM
- C. 6:00 PM
- D. 1:00 PM
Correct Answer & Rationale
Correct Answer: A
In this 24-hour analogy of Earth's history, humans appeared very recently, approximately 200,000 years ago, which is just a fraction of the total time. This corresponds to 11:58 PM, indicating that humans emerged just two minutes before the "midnight" representing the present day. Option B (9:00 PM) suggests a much earlier appearance, which does not align with the scientific timeline of human evolution. Option C (6:00 PM) is even earlier, placing humans in a time when dinosaurs were still prominent. Option D (1:00 PM) is far too early, as it would imply humans existed when early mammals were just beginning to evolve. Thus, only 11:58 PM accurately reflects the brief time humans have existed in the context of Earth's history.
In this 24-hour analogy of Earth's history, humans appeared very recently, approximately 200,000 years ago, which is just a fraction of the total time. This corresponds to 11:58 PM, indicating that humans emerged just two minutes before the "midnight" representing the present day. Option B (9:00 PM) suggests a much earlier appearance, which does not align with the scientific timeline of human evolution. Option C (6:00 PM) is even earlier, placing humans in a time when dinosaurs were still prominent. Option D (1:00 PM) is far too early, as it would imply humans existed when early mammals were just beginning to evolve. Thus, only 11:58 PM accurately reflects the brief time humans have existed in the context of Earth's history.
Other Related Questions
Which of the following is an example of physical weathering?
- A. The cracking of a rock caused by the freezing and thawing of water.
- B. Sediments being transported in a stream.
- C. A sandbar forming in a stream.
- D. Acid rain dissolving a statue.
Correct Answer & Rationale
Correct Answer: A
Physical weathering involves the mechanical breakdown of rocks without changing their chemical composition. Option A exemplifies this, as the freezing and thawing of water causes rocks to crack due to the expansion of ice, a clear physical process. Option B describes sediment transport, which is a process related to erosion rather than weathering. Option C refers to the formation of a sandbar, a depositional feature resulting from sediment accumulation, not weathering. Option D involves chemical weathering, where acid rain alters the chemical structure of the statue, distinguishing it from the physical processes in option A.
Physical weathering involves the mechanical breakdown of rocks without changing their chemical composition. Option A exemplifies this, as the freezing and thawing of water causes rocks to crack due to the expansion of ice, a clear physical process. Option B describes sediment transport, which is a process related to erosion rather than weathering. Option C refers to the formation of a sandbar, a depositional feature resulting from sediment accumulation, not weathering. Option D involves chemical weathering, where acid rain alters the chemical structure of the statue, distinguishing it from the physical processes in option A.
Which of the following best explains why an ice skater is able to coast on ice for a long distance without pushing off in a straight line across the ice?
- A. The force of friction on the blades of the skates is greater than the force of friction on the ice.
- B. The force of friction on the blades of the skates is less than the force of friction on the ice.
- C. The ice exerts a constant forward force on the skater.
- D. The buoyant force on the blades of the skates is greater than the weight of the skater.
Correct Answer & Rationale
Correct Answer: B
An ice skater can glide smoothly due to the minimal friction between the skate blades and the ice, which is significantly lower than the friction experienced on other surfaces. This reduced friction allows the skater to maintain momentum over longer distances without needing to push off. Option A is incorrect because it suggests greater friction on the blades, which would hinder movement. Option C is misleading, as the ice does not exert a forward force; instead, the skater continues moving due to existing momentum. Option D is also wrong; while buoyancy affects weight in water, it does not apply to ice skating, where weight and friction are the primary factors.
An ice skater can glide smoothly due to the minimal friction between the skate blades and the ice, which is significantly lower than the friction experienced on other surfaces. This reduced friction allows the skater to maintain momentum over longer distances without needing to push off. Option A is incorrect because it suggests greater friction on the blades, which would hinder movement. Option C is misleading, as the ice does not exert a forward force; instead, the skater continues moving due to existing momentum. Option D is also wrong; while buoyancy affects weight in water, it does not apply to ice skating, where weight and friction are the primary factors.
Which of the following best describes what happens when two magnets repel each other?
- A. The objects are pulled toward one another.
- B. The objects are pushed away from one another.
- C. An electric spark jumps from one object to another.
- D. Nothing happens until the objects are touched.
Correct Answer & Rationale
Correct Answer: B
When two magnets repel each other, they exert forces that push away from one another due to their like poles (north-north or south-south). This repulsion is a fundamental property of magnetism. Option A is incorrect because it describes attraction, which occurs when opposite poles (north-south) interact. Option C is misleading; electric sparks are not a typical result of magnet repulsion. Option D is also wrong, as repulsion occurs before any physical contact, demonstrating the active interaction between the magnets. Thus, the best description of this phenomenon is that the objects are pushed away from one another.
When two magnets repel each other, they exert forces that push away from one another due to their like poles (north-north or south-south). This repulsion is a fundamental property of magnetism. Option A is incorrect because it describes attraction, which occurs when opposite poles (north-south) interact. Option C is misleading; electric sparks are not a typical result of magnet repulsion. Option D is also wrong, as repulsion occurs before any physical contact, demonstrating the active interaction between the magnets. Thus, the best description of this phenomenon is that the objects are pushed away from one another.
Which of the following is true about the nucleus of an atom?
- A. The nucleus has a negative charge.
- B. The nucleus is neutral with no charge.
- C. The electrons and protons are located in the nucleus.
- D. The neutrons and protons are located in the nucleus.
Correct Answer & Rationale
Correct Answer: D
The nucleus of an atom is composed of protons and neutrons, making option D accurate. Protons carry a positive charge, while neutrons are neutral, contributing to the overall positive charge of the nucleus. Option A is incorrect because the nucleus does not have a negative charge; it is positively charged due to protons. Option B is also wrong, as the nucleus is not neutral; it has a positive charge from the protons. Lastly, option C is misleading because electrons are located outside the nucleus in electron shells, not within it.
The nucleus of an atom is composed of protons and neutrons, making option D accurate. Protons carry a positive charge, while neutrons are neutral, contributing to the overall positive charge of the nucleus. Option A is incorrect because the nucleus does not have a negative charge; it is positively charged due to protons. Option B is also wrong, as the nucleus is not neutral; it has a positive charge from the protons. Lastly, option C is misleading because electrons are located outside the nucleus in electron shells, not within it.