EARLY EARTH (EARTH'S FORMATION) |BeSci TV
Channel: BeSci TV
Date: 2020-10-17

BeSci TV
EARLY EARTH (EARTH'S FORMATION)

     After having watched the Earth Formation video tutorial, we now have an understanding of how our universe, solar system, and planet formed. But what was early Earth like? How did the rocks we see on the surface form?
The atmosphere? The oceans?
     Since the Earth formed through the collision and accretion of meteorites, studying what meteorites are made of helps us learn what our planet is made of. About ½ of the meteorites in our solar system are dense stony-iron and nickel; the other ½ are made of less dense carbonaceous materials. Combined together, they represent the total composition of Earth’s rocks: estimated at mass percentages of 31.9% Iron, 29.7% Oxygen, 16.1% Silicon, 15.4% Magnesium. But that composition is very different from what we see on Earth’s surface, which is 47% oxygen,28% silicon, 8% aluminum, and only 5% iron. Why? Early Earth formed through meteorite accretion would have been homogenous. Present Earth has layers. Where did these layers come from? To understand the characteristics of early Earth, we need to demonstrate the process of accretion. Take your hands – hold them as far away from each other as possible. Then bring them together quickly in a loud clap. What do you notice? Are your hands warm? The collision of your hands should have produced a large amount of heat, which causes your hands to sting and be warmer than they were before. Now imagine an early Earth formed by billions of these collisions. The continual bombardment of small asteroids combined with all the previous collisions would have produced so much heat that early Earth would have been almost entirely molten. In such a state, the material would have separated by density. The denser materials (most of the iron) would have sunk to the center to form Earth’s innermost layer known as the core. The less dense material would have risen to the top to form the outer surface layer known as the crust (mostly aluminum silicates). The remainder sits between and is known as the mantle. A similar process happens when we put chocolate and marshmallows in water – the marshmallows are less dense and float on top. The chocolate is more dense and sinks to the bottom. The water sits in the middle. Through density separation we form Earth’s three compositional layers – the crust, the mantle, and the core. When did that happen? With early Earth mostly molten, it would have all happened within in a few million years at most – so basically concurrent
with Earth’s formation – 4.6 billion years ago.