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地球是如何避免类似火星的命运的? 古老的岩石蕴藏着线索

2022年7月25日
Three illustrations showing cross sections of the Earth with different levels of the inner core, 磁力线从两极射出.

对地球的描绘, first without an inner core; second, 内心的核心开始成长, around 5.5亿年前; third, 有最外面和最里面的核心, 大约在4.5亿年前. 罗彻斯特大学 researchers used paleomagnetism to determine these two key dates in the history of the inner core, which they believe restored the planet’s magnetic field just before the explosion of life on Earth.
(美高梅开户插图/ Michael Osadciw)

New paleomagnetic research suggests Earth’s solid inner core formed 5.5亿年前 and restored our planet’s magnetic field.

大约1,美高梅在线登录脚下800英里, swirling liquid iron in the Earth’s outer core generates our planet’s protective magnetic field. This magnetic field is invisible but is vital for life on Earth’s surface because it shields the planet from solar wind—streams of radiation from the sun.

大约在5.65亿年前, 然而, the magnetic field’s strength decreased to 10 percent of its strength today. 然后, 神秘的, 球场反弹了, regaining its strength just before the Cambrian explosion of multicellular life on Earth.

是什么导致磁场反弹的?

根据科学家的最新研究 罗彻斯特大学, this rejuvenation happened within a few tens of millions of years—rapid on geological timescales—and coincided with the formation of Earth’s solid inner core, 这表明核心可能是直接原因.

“内核非常重要,”他说 约翰•塔都诺 威廉R. 小该.,地球物理学教授 地球与环境科学系 文理学院的研究主任 & 工程罗彻斯特. “就在内核开始生长之前, 磁场处于崩溃的边缘, 但当内核开始生长时, 油田重新生成.”

,发表于N原系统通信, the researchers determined several key dates in the inner core’s history, 包括更精确的年龄估计. The research provides clues about the history and future evolution of Earth and how it became a habitable planet, 以及太阳系其他行星的演化.

解开古代岩石中的信息

地球是由地壳组成的, where life is situated; the mantle, Earth’s thickest layer; the molten outer core; and the solid inner core, 这是, 反过来, 由最外面的内核和最里面的内核组成的.

地球的磁场产生于它的外核, 旋转的液态铁会产生电流, driving a phenomenon called the geodynamo that produces the magnetic field.

因为磁场与地核的关系, scientists have been trying for decades to determine how Earth’s magnetic field and core have changed throughout our planet’s history. They cannot directly measure the magnetic field due to the location and extreme temperatures of materials in the core. 幸运的是, minerals that rise to Earth’s surface contain tiny magnetic particles that lock in the direction and intensity of the magnetic field at the time the minerals cool from their molten state.

以便更好地约束内核的年龄和生长, Tarduno and his team used a CO2 laser and the lab’s superconducting quantum interference device (SQUID) magnetometer to analyze feldspar crystals from the rock anorthosite. These crystals have minute magnetic needles within them that are “perfect magnetic recorders,”塔都诺说.

By studying the magnetism locked in ancient crystals—a field known as paleomagnetism—the researchers determined two new important dates in the history of the inner core:

  • 5.5亿年前: the time at which the magnetic field began to renew rapidly after a near collapse 15 million years before that. The researchers attribute the rapid renewal of the magnetic field to the formation of a solid inner core that recharged the molten outer core and restored the magnetic field’s strength.
  • 4.5亿年前:生长中的内核结构发生变化的时间, marking the boundary between the innermost and outermost inner core. These changes in the inner core coincide with changes around the same time in the structure of the overlying mantel, 由于地表的板块构造.

“因为美高梅在线登录更精确地限制了内核的年龄, we could explore the fact that the present-day inner core is actually composed of two parts,”塔都诺说. “Plate tectonic movements on Earth’s surface indirectly affected the inner core, and the history of these movements is imprinted deep within Earth in the inner core’s structure.”

避免类似火星的命运

Better understanding the dynamics and growth of the inner core and the magnetic field has important implications, 不仅仅是揭示地球的过去和预测地球的未来, but in unraveling the ways in which other planets might form magnetic shields and sustain the conditions necessary to harbor life.

研究人员认为火星, 例如, 曾经有一个磁场, 但是磁场消散了, leaving the planet vulnerable to solar wind and the surface ocean-less. While it is unclear whether the absence of a magnetic field would have caused Earth to meet the same fate, “Earth certainly would’ve lost much more water if Earth’s magnetic field had not been regenerated,”塔都诺说. “The planet would be much drier and very different than the planet today.”

就行星进化而言, 然后, the research emphasizes the importance of a magnetic shield and a mechanism to sustain it, 他说.

“This research really highlights the need to have something like a growing inner core that sustains a magnetic field over the entire lifetime—many billions of years—of a planet.”


阅读更多

三个小月球岩石.Lunar samples solve mystery of the moon’s supposed magnetic shield

Rochester geophysicists’ latest findings contradict longstanding assumptions about whether Earth’s moon ever had a magnetic shield.

一组黄色正方形小目标的特写.Laser-driven experiments provide insights into the formation of the universe

研究ers at the Laboratory for Laser Energetics have captured 第一次 in a laboratory setting the process thought to be responsible for generating and sustaining astrophysical magnetic fields.

风绕着太阳旋转的插图.Rochester researchers uncover key clues about the solar system’s history

研究人员利用磁力来确定, 第一次, when asteroids that are rich in water and amino acids first arrived in the inner solar system.

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类别: 科学 & 技术