Unit 5-1: The Origin of the Earth
A long time ago… The first phase of Earth’s lifecycle had no atmosphere and no oceans. It was a barren, lifeless rock. Constantly heating up due to: – Compression between the rocks – Radioactive decay – Continual meteor bombardment
A long time ago… As the Earth heated up, volcanoes began to form and release steam. As the steam cooled, it condensed and collected as oceans. The atmosphere as well was formed and altered as volcanoes erupted. – The first atmospheres had no oxygen in them!
A long time ago… Oxygen began to make its way into the atmosphere by two means: – Water molecules splitting into hydrogen and oxygen due to the sunlight striking it. – Tiny little green plant cells began photosynthesis, a process that takes carbon dioxide and converts it to oxygen.
The structure of the Earth The Earth is composed of four layers: – Crust: Between 10-65km in thickness. This layer is what we live on. Made of solid, relatively light rocks – Mantle: 2850km thick. Made of heavy rocks rich in iron, magnesium and silicon. This is where magma comes from.
The structure of the Earth – Outer Core: 2100km thick. Made of liquid iron and nickel. Earthquake waves cannot pass through this layer. – Inner Core: 2800km in diameter. Made of solid iron and nickel. Although this metal is even hotter than in the outer core, the intense pressure is what keeps it solid.
Bedrock Despite outwards appearances, we are not standing directly on the Earth’s crust. There is a covering of loose rock, sand, and soil. – It can be very thick, several km, or very thin, only a few meters. – This covering is what allows plants to grow, creates mud in rivers, sand at beaches, etc.
Bedrock Beneath this loose material is the solid, unbroken segment of rock that is firmly attached to the entire mass of the Earth. – This solid rock is called bedrock. – Bedrock makes up the outermost layer of the crust. – At times, bedrock is clearly visible at the surface. – This is called an outcrop.
What’s in Bedrock (besides the Flintstones) Over a large area, the bedrock is composed of all the same type of rock. – Examples: Granite Shale Limestone But these rocks are formed from even baser materials called minerals.
Structure and Composition The minerals in the crust and upper mantle are mostly made of oxygen and silicon. The materials in the lower mantle, outer core, and inner core, are mostly iron and nickel. Where did that material come from?
Structure and Composition The metals found in the Earth did not originally come from Earth. – They came from space. – How? Meteors and other objects Meteors are made entirely of iron.
This meteor is at least as tall as I am, and much, much bigger! On display at the American Museum of Natural History in New York City.
Metal from the sky? How did the iron in a meteor get to the core? – It crashed onto the surface of the Earth. – What do you think happens when a meteor crashes to Earth? – The force of impact coupled with the intense friction of coming through the atmosphere creates a lot of heat.
Metal from the sky? As the metal in the meteor heats up, it can melt. – Molten metal sinks through the softened Earth to the center of the planet. – As more meteors crashed, more iron and nickel was added to the planets core. – This is why we have an iron core today!
Cross section of a meteor