Could a sudden sharp increase in the size and variety of ancient life have been linked to dramatic changes deep inside the Earth? About 550 million years ago, in the Cambrian (寒武纪)period of prehistory so many new animals appeared that the event is referred to as the “Cambrian explosion”. Scientists have long wondered what triggered the change, after billions of years in which life was mostly extremely small. Now it seems that the formation of Earth’s inner core—a solid iron ball at the centre of Earth—was crucial.
The inner core lies about 3,000 miles below Earth’s surface and is 1,500 miles across. It is surrounded by a liquid-metal outer core and is slowly growing as the liquid metal cools. Heat from the inner core powers swirling (旋转)movements in the liquid layer, which create a strong magnetic field (磁场)around Earth—a barrier that protects life by blocking harmful particles from outer space.
The magnetism-driving inner core seems to be a recent arrival, however. In 2019 a team led by Professor John Tarduno at the University of Rochester, New York, Us, analysed chemicals in ancient rocks from Quebec Canada, which trap a record of the magnetic field at the moment they formed. The team found that 565 million years ago, Earth’s magnetism had less than 10% of its strength today. This suggests that the swirling of liquid metal, which had always produced a protective magnetic force, was growing weak.
Now, further work has shown that the field’s strength started to recover just before the Cambrian explosion—almost certainly driven by the newly formed inner core providing a fresh power source. It seems highly likely that the two events are somehow linked.
“I don’t think that the return of Earth’s magnetic field and the subsequent explosion of life on Earth can be unconnected” says Tarduno. Working out the exact nature of the connection, however, will need a lot more scientific research.
【小题1】What does the underlined word “triggered” in Paragraph 1 mean?| A．Restricted. | B．Avoided. | C．Caused. | D．Slowed. |
| A．The inner core’s features. | B．The inner core’s structure. |
| C．The inner core’s motion. | D．The inner core’s development. |
| A．Earth’s magnetism was very weak 565 million years ago. |
| B．The inner core acts as a barrier against harmful particles. |
| C．Ancient rocks’ chemicals save a record of the magnetic field. |
| D．The field’s strength started to weaken before the Cambrian explosion. |
| A．Causes of the explosion of ancient life. |
| B．Evidence for the exact character of the link. |
| C．Research methods adopted by Tarduno-led team. |
| D．Explanations for the return of Earth’s magnetic field. |
