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Geological time and plate tectonics
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The Earth is about 4.6 billion years old. Over that time its surface has been slowly moving, joining and splitting continents.
Deep time
The Earth formed about 4.6 billion years ago. Geologists split this history into eras and periods, using evidence in rocks and fossils.
Dinosaurs died out about 66 million years ago. Modern humans appeared only about 300,000 years ago.
If the Earth's history were squeezed into one day, humans would appear in the last few seconds before midnight.
Dinosaurs died out about 66 million years ago. Modern humans appeared only about 300,000 years ago.
If the Earth's history were squeezed into one day, humans would appear in the last few seconds before midnight.
Inside the Earth
The crust is the thin rocky outer layer. Oceanic crust is thinner and denser; continental crust is thicker and less dense.
The mantle is hot rock that can flow very slowly.
The outer core is liquid metal; the inner core is solid iron and nickel, extremely hot.
The crust and top of the mantle are broken into huge pieces called tectonic plates.
The mantle is hot rock that can flow very slowly.
The outer core is liquid metal; the inner core is solid iron and nickel, extremely hot.
The crust and top of the mantle are broken into huge pieces called tectonic plates.
Moving continents
In 1912 Alfred Wegener proposed continental drift: the continents were once joined.
Evidence: South America and Africa fit together like a jigsaw; the same fossils and rock types are found on both.
There was once a supercontinent called Pangaea, which began to break apart about 200 million years ago.
Plates move a few centimetres a year, about as fast as your fingernails grow. Heat from inside the Earth drives this movement.
Evidence: South America and Africa fit together like a jigsaw; the same fossils and rock types are found on both.
There was once a supercontinent called Pangaea, which began to break apart about 200 million years ago.
Plates move a few centimetres a year, about as fast as your fingernails grow. Heat from inside the Earth drives this movement.
Give two pieces of evidence that South America and Africa were once joined.
- The coastlines of eastern South America and western Africa fit together like jigsaw pieces.
- Fossils of the same ancient animals and plants are found on both continents.
- Matching rock types and ages appear on both sides of the Atlantic.
Answer: The jigsaw fit of coastlines and matching fossils (and rocks) on both continents.
Earth: about 4.6 billion years old. Layers: crust (oceanic thin and dense; continental thick and light), mantle, liquid outer core, solid inner core. Wegener (1912): continental drift; Pangaea broke up from about 200 million years ago. Plates move a few cm a year.
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