- 3502 - EARTH - early Earth formation? Earth formed from the Sun’s proto-planetary disk about 4,600,000,000 years ago. In the beginning, it was a molten spheroid with scorching temperatures. Over time, it cooled, and a solid crust formed. Eventually, the atmosphere cooled, and life became a possibility.
--------------------- 3502 - EARTH - early Earth formation?
- The atmosphere on early Earth was rich in carbon, and that carbon had to be removed before the temperature could drop and Earth could become habitable. Where did all the carbon go?
-
- The first 500,000,000 years of Earth’s existence are informally called the “Hadean eon“. The name comes from Hades, the Greek God of the Underworld. Hades is also an informal name for Hell itself.
-
- The “Hadean eon” is aptly named. Even after it began to cool and solidify, Earth was still scorching hot. The atmosphere contained 100,000 times the current level of atmospheric carbon.
-
- Early Earth was similar to Venus, where a thick atmosphere traps heat and keeps temperatures high. During the Hadean, Earth’s surface temperature exceeded 200 Celsius (400 F.)
-
- Before Earth could cool, it had to scrub a lot of carbon from its atmosphere. But scientists have found it challenging to piece together events on the very young Earth. For one thing, the geological evidence is scant. But, there is a new explanation for removing all that atmospheric carbon, and it involves a type of rock that no longer exists.
-
- Geological evidence shows that Earth’s surface environment was similar to present-day Earth’s by the middle of the Hadean. A few things had to happen before Earth could be habitable. Oceans had to form, plate tectonics had to start, and greenhouse gases had to be removed quickly from the atmosphere.
-
- A massive amount of atmospheric carbon had to be removed. Because there is no rock record preserved from the early Earth. It was a magma ocean, a sphere of molten rock and nothing else.
-
- During this phase, the planet was forming via accretion. In the accretion process, materials agglomerate together creating a large object over time. Earth took between 70 million and 100 million years to assemble. During that time, planetesimals slammed into the Earth-to-be, generating heat and keeping Earth in a molten state.
-
- Plantisesimals are spherical , large asteroids that are too small to be called a planet and too big to be called an asteroid.
-
- The magma ocean is an essential stage in the life of rocky planets. The liquid state allows heavier elements to sink to the core and lighter elements to “float” on top. This is how planets like Earth become differentiated into layers, a core, a mantle, and a crust. The inner core is still molten to this day, and without it, Earth would have no protective magnetosphere and probably no life.
-
- When Earth’s magma ocean solidified, it released massive quantities of greenhouse gases into the atmosphere. As a result, Earth’s early atmosphere contained a lot of CO2 and H2O. Those gases helped maintain the young planet’s extreme climate.
-
- For that climate to become more moderate within the timeframe of the Hadean, things had to change rapidly, in geological terms. Those greenhouses gases had to be removed, and the only repository for them was the rock.
-
- As part of Earth’s carbon cycle, carbon is sequestered into rock through transformation into carbonate minerals in ocean basins. From there, the carbonates become part of the mantle. Even some of the carbon we’re emitting now will be subducted and end up as diamonds in the distant future.
-
- If the climate was moderate and similar to modern Earth’s 4 billion years ago, the carbon sequestration had to be very efficient.
-
- During the Hadean eon, Earth had what’s called a “wet mantle“. The mantle is 1,900 mile thick layer of rock. A wet mantle is one that contains a high proportion of water, and that water affects convection.
-
- Earth’s mantle contains a lot of silicate minerals, and they were molten during the Hadean. Water lowers the melting point of silicates, keeping more of the silicates molten. Convection currents in the molten material meant that the mantle experienced convection.
-
- That means that the wet mantle experienced more convection, which brought more of the magnesium-rich minerals to the surface where it could react with carbon. In effect, the mantle surface recycled itself more rapidly, bringing new magnesium into contact with carbon more rapidly. Eventually that carbon was removed from the atmosphere and sequestered into the mantle.
-
- The mantle had to be chemically heterogenous. That means the composition wasn’t uniform, but instead consisted of different and diverse constituents. In chemistry it denoting a process involving substances in different phases (solid, liquid, or gaseous).
-
- Habitability required not only active plate tectonics and removal of green house gases from the atmosphere, bit also required oceans. A heterogeneous mantle has more convection, which exposes more magnesium-rich rocks to the atmosphere. That’s what removes green house gases from the atmosphere, cooling to more modern day temperatures.
-
- The temperature was high enough to vaporize the water, but the pressure was high, too. The surface temperature exceeds 100°C owing to the greenhouse effect, yet liquid water is stabilized by high atmospheric pressure.
-
- This is how the Earth got started. Now , how did life get started?
-
March 13, 2022 EARTH - early Earth formation? 3502
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ---
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
--------------------- --- Friday, March 18, 2022 ---------------------------
No comments:
Post a Comment