Earth’s history

Geologic time Lesson 1

Evidence that earth has changed – Rock layers The principle of superposition states that in rock layers that have not been folded or deformed, the oldest rock layers are on the bottom This gives the relative age of the rocks

Rock layers The largest sediment particles are usually deposited near the bottom of a rock layer

fossils The preserved remains or evidence of past living organisms are called fossils

https://www.brainpop.com/science/diversityoflife/fossils/

radioactivity Radioactive decay is the process by which an element naturally changes into another The original element is called the parent element and the new element that forms is called the daughter element.

https://www.brainpop.com/science/energy/radioactivity/

If you start with 1,000 atoms, how many atoms would remain after 2 half-lives? After one half-life = 500 atoms After two half-lives = 250 atoms

https://www.brainpop.com/science/earthsystem/geologictime/

Geologic time scale The geologic time scale is a visual record of Earth’s history, with the individual units based on changes in the rocks and fossils. Geologists divide Earth’s history into eons, eras, periods, and epochs.

Imagine…

Slow vs. fast changes Fast changes Erosion Weathering Deposition Slow changes Fast changes Erosion Weathering Deposition Landslides Volcanic eruptions Earthquakes

Ancient earth Lesson 2

Gravity and the solar system The solar system started as a nebula, a cloud of gas, ice, and dust. Gravity pulled the particles together into a flattened disk shape that began to rotate.

Spherical earth Earth became larger as more particles came together Collisions produce thermal energy, so the colliding particles warmed the new planet

https://ed.ted.com/on/yRWszobe

Spherical Earth Gravity pulled the hot rocks into the shape of a sphere Asteroids continued to crash into the surface, making Earth even hotter

Hadean eon It was very hot during the Hadean eon due to collisions with asteroids and large amounts of radioactive decay

Hadean eon During the Hadean Eon there was: Formation of Earth’s core Cooling Seas of molten rock Small islands of solid rock

Early atmosphere During the Hadean eon, there was an atmosphere of water vapor, carbon dioxide, and poisonous gases (no oxygen) due to volcanic activity

The Archean eon During the Archean eon, the temperature dropped Earth had its first solid surface The Archean continents were called protocontinents

The Archean eon The temperature drop led to the condensation of water vapor The rain was acidic and dissolved salts forming salty oceans

The Archean eon The earliest evidence of life is present in rocks that formed in the warm Archean oceans

The Proterozoic eon The Earth continued to cool during the Proterozoic eon There was an increase in oxygen The Snowball Earth hypothesis suggest the whole Earth was covered with ice

The Proterozoic eon The first multicellular organisms evolved in the oceans

The Cambrian explosion Lesson 3

The Cambrian explosion The change in life on Earth during the beginning of the Phanerozoic eon is known as the Cambrian Explosion

The Cambrian explosion (continued) Scientists hypothesize that continents were breaking apart, temperatures were increasing, and sea levels were rising Some organisms became adapted to the new environment

https://www.brainpop.com/science/diversityoflife/dinosaurs/

The impact of asteroids Scientists hypothesize that an asteroid impact might have contributed to the mass extinction that occurred at the end of the Cretaceous period Many animals, including dinosaurs, became extinct

https://www.brainpop.com/science/ourfragileenvironment/extinction/

Earth’s changing surface Volcanic activity has decreased, but continues today forming oceanic crust, building mountains, and powering the rock cycle Mountains continue to build as plates move