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500 million years of climate history recorded on tectonic plates



The Indonesian volcano Paluveh is located in the region of tectonic plates that collide - perhaps the formula for glacial periods in geological history.
Enlarge / T The Indonesian volcano Paluveh is located in the region of tectonic plates that collide – perhaps the formula for glacial periods in geological history.

Generally speaking, it's easy to understand the last several million years of climate patterns – the world looked the way it does today, so changes in greenhouse gas concentrations or ocean circulation can be linked to what we see now. But as you go back in time, you can find a very different climate and a reorganized map of the continents, and they require more creative thinking.

For example, Ice Age periods in the recent past are not unique. However, most of the last 500 million years was much warmer – what caused the climate slowly to move toward warmer or cooler temperatures over a million years?

Looping

In the great sweep of Earth's history, its climate has remained at a favorable temperature range – thanks to the partially moderate influence of feedback loops within the system. Exposure to silicate minerals in a stone substrate is withdrawn by CO2 from the atmosphere, for example. In climatic conditions, heating can accelerate, remove more greenhouse gases and stabilize temperatures. Cool down the planet and slow down the weather conditions, giving more greenhouse gases chances to accumulate.

(This takes place in a geological time frame – it will not help us in the next century. But this is an important long term thermostat.)

But the Earth was like a house full of passive-aggressive roommates, with a default point on the thermostat as if it were periodically changing. Calling on geology to explain these major changes more or less comes down to two options: either the release of CO2 a change in volcanic activity, or something that intensifies CO suction processes2 from the atmosphere. In recent years, researchers have compared these things with a climate change pattern to see how they correlate.

A new study by Francis MacDonald from the University of California, Santa Barbara, is a powerful argument for the tectonics of thermostatic-controlled thermostatic plates between collisions between volcanic islands and larger continents – especially in tropics.

The idea is not new. Such events are good candidates for air conditioning drivers. When one of these "volcanic arches" collides with the continent, volcanoes die and stop releasing CO2. But more importantly, some of their magmatic rocks are crumbling on the continent. Researchers say this exposed magma wall is extremely effective in removing CO2 when time passes. Tectonic pressing continues to push and rock, preventing it from being buried and keeping it exposed to weather influences.

In tropical areas, warmer temperatures and abundant rainfalls are ideal for maximizing the process of wear – even during glacial periods when huge ice covers are closer to the poles. The number of these crashes at any time – and their location – is quite a big car accident. So, if several major collisions occur in tropical regions for several million years, the impact on the amount of CO2 in the atmosphere can be significant.

Maps of collisions of volcanic arches and continents 0, 250, 300 and 445 million years. Modern locations are shown on the top left map. "Src =" https: //cdn.arstechnica.net/vp-content/uploads/2019/03/macdonald_fig_map-640k329.png "vidth =" 640 "height =" 329 "srcset =" https: //cdn.arstechnica .net / vp-content / uploads / 2019/03 / macdonald_fig_map-1280k658.png 2k
Enlarge / T Maps of collisions of volcanic arches and continents 0, 250, 300 and 445 million years. Modern locations are shown on the top left map.

To test this idea on a good sample of Earth's history, researchers have compiled a map of reconstructed tectonic collisions of plates (sometimes called "seams", as cracks will collapse) that return to the Cambrian period 540 million years ago. They compared this with the recorded evidence of ice cover, noting how close it is to ice coverage in the equator.

Strong correlation

Their hypothesis looked good. Correlation between collisions with volcanic onions and the continent in tropical regions and ice cover is very good. The largest period of glaciers agrees with the times when these collisions ranged from 10,000 to 14,000 kilometers, exposing quite a lot of dangerous rocks. In other, warmer times, the length of these tropical crashes fell to 4,000 kilometers or less.

If you turn on crashes outside of the tropics, the correlation is a bit weaker. This is not surprising, since the walls exposed to high-latitude collisions would not be so quick.

Researchers claim that the overall picture supports the idea of ​​removing CO2 through atmospheric influences is more important than the change in CO emission2 from volcanoes. If the key release of volcanoes is, the global correlation would be at least as good as a tropical correlation, because it does not matter where CO2 gets released.

Time lines of tectonic collisions of plates ("seams") and degree of ice cover. The chart above shows the total length of global collisions, while the middle chart shows only collisions in tropics. "Src =" https: //cdn.arstechnica.net/vp-content/uploads/2019/03/macdonald_fig_corr.png "vidth =" 527 "height =" 861

Time lines of tectonic collisions of plates ("seams") and degree of ice cover. The chart above shows the total length of global collisions, while the middle chart shows only collisions in tropics.

The researchers compared ice coverage with several different types of volcanic activity in a similar way. There is a certain correlation with the length of the continental lines of volcanoes (like modern Andes or cascades), but that's not nearly as good. The other idea is that they are rare, but massive eruptions – such as lions for Deccan traps that cover a large part of what is now India – sprinkled huge amounts of rocks that can be felt in the tropics. But the correlation with this kind of activity in this analysis seems pretty bad.

This leaves the researchers a proper explanation for really long-term climate change in the past. "[O]the model is an account for both the initiation and the end of the Ice Age, "they write. "This pattern was repeated at least three times in progress [last 540 million years]- When it was abundant [of weatherable rock] Exhumed and eroded in the tropics, the Earth was in the state of an iceberg, and when it was not, the Earth was in an ice-free climatic condition.

ScienceDOI: 10.1126 / science.aav5300.


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