Study: Earth’s Inner Core May Be Changing Speed

Study: Earth’s Inner Core May Be Changing Speed

A recent study suggests that the rate at which the Earth's center is turning is slowing down compared to the outer parts of the planet.

Earth scientists, or geologists¹, say that the center or core of the Earth can rotate, or turn, at a different rate than the outer areas.

The latest research appeared in the scientific publication Nature Geoscience.

The writers of the research are Xiaodong Song and Yi Yang of China's Peking University in Beijing. They used information about seismic² waves from earthquakes to study the core.

Earth's inner core is a ball of hot iron that is a little smaller than the Moon. Because it floats in the liquid metal of the outer core, it can spin at a different speed than the rest of the planet.

In the 1930s, scientists discovered the Earth's core by studying changes in the speed of seismic waves as they travelled through the planet. The changes in speed showed that the core was a solid center made mostly of iron.

The new research by Song and Yang studied what they called "repeated seismic waves from the early 1990s." They looked for changes in the amount of time seismic waves take to travel over the same paths inside the Earth.

The scientists suggest changes in the spin of Earth's core can explain the changes in travel times.

"We believe the inner core rotates, relative to the Earth's surface, back and forth³, like a swing," they told The French news agency AFP. They added that its relative rotation⁴ changes about once every 35 years.

They also said these changes correspond with very small changes in "length of day"—the exact amount of time it takes for Earth to rotate on its axis⁵.

Different research results

In June 2022, John Vidale and Wei Wang, Earth scientists at the University of Southern California (USC), published a study in Science Advances.

They reported that between 1969 and 1971 the core rotated more slowly than the outer layers. They also said that after 1971, the core rotated faster than the outer layers. In their study, Wang and Vidale used data on seismic waves from nuclear test explosions.

Earth scientists say the Earth's core is difficult to understand and study. They disagree about how much, and how often, the spin might change. Some scientists argue that the speed of the spin does not change at all. They say the changes in seismic waves are caused by changes on the surface of the inner core instead of differences in how fast the core is spinning.

Hrvoje Tkalcic is a geophysicist at the Australian National University. He thinks scientists will disagree about the latest research.

He compared seismologists, who study earthquakes and seismic waves, to doctors "who study the internal organs of patients' bodies using imperfect or limited equipment." He added: "Our image of the inner Earth is still blurry⁶."

Song and Yang said scientists need years of seismic data to answer questions about Earth's core.

Vidale of USC said, "Something's happening and I think we're going to figure it out. But it may take a decade."

Words in This Story

core –n. the very center of something

spin –v. to turn

seismic –adj. related to earthquakes

swing –v. to move back and forth between two positions

correspond with –v. (phrasal) to have a direct relationship to or with something or someone

imperfect –adj. having some fault or incomplete part or area

blurry –adj. unclear

figure (something) out –v. (phrasal) to understand or find something by thought

decade –n. a 10-year period

1 geologists   

地质学家，地质学者( geologist的名词复数 )

参考例句：

• Geologists uncovered the hidden riches. 地质学家发现了地下的宝藏。
• Geologists study the structure of the rocks. 地质学家研究岩石结构。

2 seismic   

a.地震的，地震强度的

参考例句：

• Earthquakes produce two types of seismic waves.地震产生两种地震波。
• The latest seismic activity was also felt in northern Kenya.肯尼亚北部也感觉到了最近的地震活动。

3 forth   

adv.向前；向外，往外

参考例句：

• The wind moved the trees gently back and forth.风吹得树轻轻地来回摇晃。
• He gave forth a series of works in rapid succession.他很快连续发表了一系列的作品。

4 rotation   

n.旋转；循环，轮流

参考例句：

• Crop rotation helps prevent soil erosion.农作物轮作有助于防止水土流失。
• The workers in this workshop do day and night shifts in weekly rotation.这个车间的工人上白班和上夜班每周轮换一次。

5 axis   

n.轴，轴线，中心线；坐标轴，基准线

参考例句：

• The earth's axis is the line between the North and South Poles.地轴是南北极之间的线。
• The axis of a circle is its diameter.圆的轴线是其直径。

6 blurry   

adj.模糊的；污脏的，污斑的

参考例句：

• My blurry vision makes it hard to drive. 我的视力有点模糊，使得开起车来相当吃力。 来自《简明英汉词典》
• The lines are pretty blurry at this point. 界线在这个时候是很模糊的。 来自《简明英汉词典》