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Unsolved Mysteries about the Planet Earth
Mystery 1: Where did water come from?
Water covers more than 70 percent of the Earth’s surface and that makes the Earth earn the nickname “the blue planet”. Then where did water come from? The most popular scientific theory states that the H2O came from several violent asteroids(小行星) covered with ice. Another suggests that the water actually has been around since the Earth’s formation. However it happened, though, it’s certainly worked out well for the Earth life forms.
Mystery 2: What about all the oxygen?
Another thing is the planet’s oxygen. Tiny creatures released oxygen as a waste product, filling the atmosphere with it. After that, the level of oxygen in the Earth’s atmosphere went wildly up and down until it finally calmed down around 540 million years ago. Since then, it’s remained at about the breathable level we know today. But what caused it to be suddenly steady?
Mystery 3: What caused the Cambrian(寒武纪）Explosion?
The Cambrian Explosion refers to the explosion of complex life forms that occurred on Earth about 540 million years ago. Before then, life had consisted mostly of microbes. But at the beginning of the Cambrian period complex creatures began developing at a rate never seen before. Suddenly, life forms had brains, eyes, and bones. Most living creatures today can trace their blood back to the Cambrian period.
Mystery 4: Will we be able to predict earthquakes?
We still haven’t been able to come up with a way to accurately predict earthquakes. We can certainly try, but our current technology cannot predict them exactly. We know that earthquakes start when the rock cracks underground and the enormous energy released in the process causes vibration, which generates earthquake waves, but we haven’t figured out why that happens, or how to predict it.
1. What was created by creatures on Earth?
A. Water. B. Oxygen.
C. Bacterium. D. Ice.
2. Which of the following talks about the Earth’s advanced species?
A. Mystery 1. B. Mystery 2.
C. Mystery 3. D. Mystery 4.
3. What do we know about Mystery 4?
A. It is a matter that has extremely practical significance.
B. It will be solved in the near future.
C. It is the most difficult mystery to solve of the four.
D. It is the oldest mystery of the four.
