Classroom Notes:
“How the Earth was made”
How was Earth formed?
Theory: Sun was surrounded by gas and dust. The particles on the outer reaches of the solar nebula clumped together through static electricity.
Evidence: Astronaut was conducting an investigation of how matter behaved in the zero gravity of space. He tested salt. He put the salt grains in a plastic bag and shook it. The salt particles began to clump together proving that smaller particles will clump together because of static electricity between particles in space.
**The process of particles clumping together to form larger particles is ACCRETION
** Took 30 million years for accretion to form the Earth to the size it is today.
Theory: The Earth became molten rock soon after its formation. Radioactive elements provided the increase in temperature to melt the rock.
Evidence: The Earth is in different layers (crust, mantle and core). If the rock was molten, the elements would have separated based on their density differences, with heavier elements like iron (Fe) and Nickel (Ni) sinking to the center. This process is called DIFFERENTIATION.
How old is the Earth (and the entire solar system)?
We had no theory about its age prior to finding evidence. The oldest Earth’s rock didn’t seem old enough.
Evidence: The Earth’s rocks were not reliable measure due to plate tectonic movement and erosion. Scientists use radiometric dating to find the age of meteorites. Since it is believed that they were formed at the same time as Earth and the rest of the solar system, they are a reliable source. Current studies show Earth is 4.57 billion years old.
How did the moon form?
Original theory: Moon was same as our Earth, same composition, layers, has a core, etc.
Evidence: Moon rocks contained much less iron (Fe) than geologists expected. Their composition was similar to that of the Earth’s crust and upper mantle.
New theory: A small planet collided with early Earth, ripping off part of the crust and upper mantle. The planet didn’t survive but the material ripped from Earth formed our moon.
How did Earth get to look like it does today?
Evidence: Amphibolite (a type of rock) found in Hudson Bay, Canada were dated to be 4. 28 billion years old. This is the closest we have come to Earth’s original crust. The minerals in the amphibolite suggest that they were formed 12 miles below the surface.
Supports the Theory: that the Earth had a crust that was at least 12 miles thick 4. 28 billion years ago.
Evidence: The composition of amphibolite suggests it was formed under water (or on an ocean floor). Iron banded formations found in the same geologic column contained magnetite. Magnetite can only form in an ocean environment.
Supports the theory: that the Earth had an ocean 4.28 billion years ago.
Where did the water come from?
Original theory: icy comets entering Earth’s atmosphere evaporated the water into the atmosphere which eventually fell to the Earth as rain. Earth’s first water was fresh water. Weathering of rocks carried salts to the oceans.
Evidence: Meteorites that fell to the Earth were found to contain table salt. Within the salt grains were microscopic drops of water. The salt and water has been dated to be 4.5 billion years old (when the solar system first formed).
Supports the new theory: Most of the water came from the meteorites bombarding the Earth.
How did life form on Earth?
Original theory: Amino acids (the chemical building blocks of life) were formed through chemical reactions on Earth.
Evidence: Scientists discovered that meteorites contain amino acids.
Supports the new theory: The amino acids came from space (meteorites).
How did we get an oxygenated atmosphere?
3.5 billion years ago there was no oxygen in our atmosphere. Our atmosphere was created through OUTGASSING. This is the process by which volcanoes released gases into the atmosphere during an eruption. Our early atmosphere was toxic, containing sulfur, carbon dioxide, methane and sulfuric acid. 3.5 billion years ago there was primitive microbial life. Stromatalite is a structure created by the microbial life, cyanobacteria.
Evidence: Living stromatalite is rare, but scientists have found evidence that the cyanobacteria produce oxygen that is released into the atmosphere.
Theory: Cyanobacteria production of oxygen is responsible for the oxygenation of our atmosphere.