How much do you know about Earth—the planet that we live on? Our knowledge of Earth has been developing since ancient times. However, many puzzles (谜) about Earth remain unsolved. Live Science has published a list of the eight biggest mysteries about Earth. Let’s look at some of them.
Where did water come from?
When it first came into being 4.5 billion years ago, Earth was a dry rock. So where did all of our water come from? Scientists think that it might have arrived in the form of ice by an asteroid (小行星) from outer space that hit our planet. But this idea has not been confirmed (证明) because there is very little related evidence(相关证据) to be studied.
What’s in the core (地核)?
Scientists used to study meteorites (陨石) as small examples of Earth, believing that Earth’s core was made of iron and nickel (镍). However, a later study in the 1950s proved this way to be wrong because it found that Earth would be too light to provide gravity (引力) if its core contained only iron and nickel. Today, scientists continue to bring forward different ideas, but none have been confirmed.
How was the moon born?
Scientists have found that the chemical compositions (成分) of Earth and the Moon are very similar. That suggests that the Moon actually came from Earth. For example, it could be a piece of Earth that separated when Earth hit another planet. It is also possible that when Earth first came into being, it spun (旋转) very fast and threw off enough molten (熔化的) rock to later form the Moon.
【小题1】What’s the main idea of the passage?| A．How Earth came into being. |
| B．Where Earth’s water came from? |
| C．How the moon was formed? |
| D．Unexplained mysteries about Earth. |
| A．Earth’s water may come from ice that melted 4.5 billion years ago. |
| B．Earth’s water may come from a small planet that hit Earth. |
| C．We don’t know where water came from. |
| D．There is lots of evidence that tells us where water came from. |
| A．Check | B．Raise |
| C．Improve | D．Receive |
| A．Scientists used to believe Earth’s core was made of meteorites. |
| B．A study in the 1950s proved that Earth’s core is made of iron and nickel. |
| C．The moon and Earth are made of similar materials. |
| D．Three possibilities of where the Moon came from are mentioned. |
