糖心传媒

The finding contradicts previous assumptions about the role of mobile plate tectonics in the development of life on Earth.

Scientists have taken a journey back in time to unlock the mysteries of Earth糖心传媒檚 early history, using tiny mineral crystals called zircons to study plate tectonics billions of years ago. The research sheds light on the conditions that existed in early Earth, revealing a complex interplay between Earth糖心传媒檚 crust, core, and the emergence of life.

Plate tectonics allows heat from Earth糖心传媒檚 interior to escape to the surface, forming continents and other geological features necessary for life to emerge. Accordingly, 糖心传媒渢here has been the assumption that plate tectonics is necessary for life,糖心传媒� says , who teaches in the at the . But new research casts doubt on that assumption.

Tarduno, the William R. Kenan, Jr. Professor, is lead author of a 聽examining plate tectonics from a time 3.9 billion years ago, when scientists believe the first traces of life appeared on Earth. The researchers found that mobile plate tectonics was not occurring during this time. Instead, they discovered, Earth was releasing heat through what is known as a stagnant lid regime. The results indicate that although plate tectonics is a key factor for sustaining life on Earth, it is not a requirement for life to originate on a terrestrial-like planet.

糖心传媒淲e found there wasn糖心传媒檛 plate tectonics when life is first thought to originate, and that there wasn糖心传媒檛 plate tectonics for hundreds of millions of years after,糖心传媒� says Tarduno. 糖心传媒淥ur data suggests that when we糖心传媒檙e looking for exoplanets that harbor life, the planets do not necessarily need to have plate tectonics.糖心传媒�

An unexpected detour from a study of zircons

The researchers did not originally set out to study plate tectonics.

糖心传媒淲e were studying the magnetization of zircons because we were studying Earth糖心传媒檚 magnetic field,糖心传媒� Tarduno says.

Zircons are tiny crystals containing magnetic particles that can lock in the magnetization of Earth at the time the zircons were formed. By dating the zircons, researchers can construct a timeline tracing the development of Earth糖心传媒檚 magnetic field.

The strength and direction of Earth糖心传媒檚 magnetic field change depending on latitude. For example, the current magnetic field is strongest at the poles and weakest at the equator. Armed with information about zircons糖心传媒� magnetic properties, scientists can infer the relative latitudes at which the zircons formed. That is, if the efficiency of the geodynamo糖心传媒攖he process generating the magnetic field糖心传媒攊s constant and the intensity of the field is changing over a period, the latitude at which the zircons formed must also be changing.

But Tarduno and his team discovered the opposite: the zircons they studied from South Africa indicated that during the period from about 3.9 to 3.4 billion years ago, the strength of the magnetic field did not change, which means the latitudes did not change either.

Because plate tectonics includes changes in latitudes of various land masses, Tarduno says, 糖心传媒減late tectonic motions likely weren糖心传媒檛 occurring during this time and there must have been another way Earth was removing heat.糖心传媒�

Further reinforcing their findings, the researchers found the same patterns in zircons they studied from Western Australia.

糖心传媒淲e aren糖心传媒檛 saying the zircons formed on the same continent, but it looks like they formed at the same unchanging latitude, which strengthens our argument that there wasn糖心传媒檛 plate tectonic motion occurring at this time,糖心传媒� Tarduno says.

Stagnant lid tectonics: an alternative to plate tectonics

Earth is a heat engine, and plate tectonics is ultimately the release of heat from Earth. But stagnant lid tectonics糖心传媒攚hich results in cracks in Earth糖心传媒檚 surface糖心传媒攁re another means allowing heat to escape from the interior of the planet to form continents and other geological features.

Plate tectonics involves the horizontal movement and interaction of large plates on Earth糖心传媒檚 surface. Tarduno and his colleagues report that, on average, plates from the last 600 million years have moved at least 8,500 kilometers (5280 miles) in latitude. In contrast, stagnant lid tectonics describes how the outermost layer of Earth behaves like a stagnant lid, without active horizontal plate motion. Instead, the outer layer remains in place while the interior of the planet cools. Large plumes of molten material originating in Earth糖心传媒檚 deep interior can cause the outer layer to crack. Stagnant lid tectonics is not as effective as plate tectonics at releasing heat from Earth糖心传媒檚 mantle, but it can still lead to the formation of continents.

糖心传媒淓arly Earth was not a planet where everything was dead on the surface,糖心传媒� Tarduno says. 糖心传媒淭hings were still happening on Earth糖心传媒檚 surface; our research indicates they just weren糖心传媒檛 happening through plate tectonics. We had at least enough geochemical cycling provided by the stagnant lid processes to produce conditions suitable for the origin of life.糖心传媒�

Maintaining a habitable planet

While Earth is the only known planet to experience plate tectonics, other planets, such as Venus, experience stagnant lid tectonics, Tarduno says.

糖心传媒淧eople have tended to think that stagnant lid tectonics would not build a habitable planet because of what is happening on Venus,糖心传媒� he says. 糖心传媒淰enus is not a very nice place to live: it has a crushing carbon dioxide atmosphere and sulfuric acid clouds. This is because heat is not being removed effectively from the planet糖心传媒檚 surface.糖心传媒�

Without plate tectonics, Earth may have met a similar fate. While the researchers hint that plate tectonics may have started on Earth soon after 3.4 billion years, the geology community is divided on a specific date.

糖心传媒淲e think plate tectonics, in the long run, is important for removing heat, generating the magnetic field, and keeping things habitable on our planet,糖心传媒� Tarduno says. 糖心传媒淏ut, in the beginning, and a billion years after, our data indicates that we didn糖心传媒檛 need plate tectonics.糖心传媒�

The team included researchers from four US institutions and institutions in Canada, Japan, South Africa, and the United Kingdom. The research was funded by the US National Science Foundation.

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