1. Geologic Time Scale
MYP 2

2. Evidence that Earth Has cHANGED
Scientists study Earth’s past, and they develop ideas and theories about how it formed and how it has changed.
Evidence that Earth Has cHANGED

3. Rock Layers and Fossils
Weathering breaks down rocks exposed at the Earth’s surface into smaller pieces called sediment.
Water, wind and gravity move the sediment along to form basins.
Over time the increasing weight cause layers to compress which give us different layers of rock.
Rock Layers and Fossils

4. Rock Layers and Fossils
Older layers of rock tend to be on the bottom while new layers of rock tend to be on top.
Geologists use this information in order to estimate the age of the layers and anything in them.
Principle of Superposition: states that in rock layers that have not been folded or deformed, the oldest rock layers are on the bottom.
Sometimes organisms get trapped in the different layers and under certain conditions those organisms also become rock.
Fossils are the preserved remains or evidence of past living organisms.
Rock Layers and Fossils

5. Radioactivity Atoms make up all matter on Earth.
Elements are substances that are made up of atoms.
Most elements are completely stable, and others are unstable.
The unstable ones will break down or decay over time make different elements,
Radioactive Decay is the process by which one element naturally changes into another.
Radioactivity

6. A radioactive element decays at a rate that is constant for that specific element.
Scientists have calculated those rates.
The half –life of an element is the time required for half of the amount of a radioactive parent element to decay into a stable daughter element.
Because of the rate of decay is constant we can use them as a clock to measure the time a fossil has been in the ground.
Radioactivity

7. The Geologic Time Scale
It is a visual record of Earth’s history, with the individual units based on changes in the rocks and fossils.
The Geologic Time Scale

8. Eons, Eras, Periods, AND ePOCHS
Geologic time scale shows the units used to describe Earth’s history.
The divisions are not all the same, but mark places in the rock record where there are significant changes in the type of fossils present in the rocks.
Eons, Eras, Periods, AND ePOCHS

9. Comparing Time Scales Earth is 4.6 Billion years old.
Imagine all of Earth’s history taking place in a year with January 1st being the start day.
The first tiny organisms to float on the ocean would arrive on February 21.
The earliest animals to crawl onto land would be November 20.
The last of the dinosaurs to be extinct happens on December 25.
And human ancestors would first appear on December 31.
Comparing Time Scales

10. Ancient Earth
MYP 2

11. Gravity and the Solar System
Before the solar system existed there was a nebula, a big cloud of gas, ice, and dust.
Gravity pulled the particles together to make a flatten disk shape that started rotating.
The center of this disk became dense and the sun formed.
Last, the pieces of material remaining in the disk attracted each other, and the planets formed.
Gravity and the Solar System

12. Spherical Earth Earth became larger as more particles came together.
Thermal energy was created because of the many collisions that took place on the surface of the Earth, which warmed the planet.
Because the rocks were soft enough to flow gravity pulled them into the shape of a sphere.
Spherical Earth

13. Earth had large amounts of radioactive elements that as they were decaying were producing thermal energy.
Early Earth was much hotter than it is today.
Because of this, this time period of Earth’s history is named after the Greek God of the Underworld Hades.
The Hadeon Eon is the first 640 million years of Earth’s history.
Hadean eon

14. When Earth’s particles became hot enough to melt metal, the denser metal was pulled to the core by gravity.
Fewer and fewer asteroids were hitting the surface of the Earth so the surface started to cool.
There were seas of molten rock that covered the earth and when that cooled started to form an ancient crust.
Volcanic gases formed the Earth’s atmosphere making it nearly impossible to have modern humans existing at the time.
Hadean eon

15. This is the period of time that occurred from about 4-2
This is the period of time that occurred from about billion years ago.
Earth had it’s first solid surface and portions of that crust still exist on most of Earth’s continents.
Still produced 2x as much thermal energy as Earth does today.
The oldest rocks on Earth are from the Archean Eon.
Archean Eon

16. Archean Eon Volcanic eruptions formed the first oceanic crusts.
Convection currents, formed by the rising and sinking of hot material below Earth’s surface, moved the crust along Earth’s surface.
Protocontinents (small early continents from the Archean Eon) existed.
Archean Eon

17. Because the temperature dropped, water vapor in the air condensed and it started to rain.
Since it was acidic rain it dissolved mineral salts from the rocks which created to salty ocean water.
The earliest forms of life still exist today as blue green algae.
The algae combined with sediment created what’s called a stromatolite.
Archean Eon

18. Proterozoic Eon Took place from 2.5-o.542 billion years ago
Procontinents collided to create larger landmasses much like the ones of today.
Oxygen was being produced through photosynthesis and the sun splicing molecules.
Created the Oxygen Catastrophe because most species at the time could not have that much oxygen present in the atmosphere.
Proterozoic Eon

19. Rodinia was a supercontinent that existed that had shallow ocean coasts that are similar to the coasts we have today.
Unicellular organisms were predominant and life was mainly in the water.
At the end of this eon the first multicellular organisms evolved in the oceans.
Proterozoic Eon

20. The Cambrian Explosion
MYP 2

21. The Cambrian Explosion
Occurred during the Phanerozoic eon- the time in Earth’s history from 542 million years ago to the present.
Phanerozoic rocks contain a large number of fossils that are large enough to see without a magnifying device.
Cambrian period is the beginning of the Phanerozoic eon.
The Cambrian Explosion refers to the change and great diversity of the organisms that were present on Earth.
The Cambrian Explosion

22. The Cambrian Explosion
Scientists hypothesize that the Cambrian Explosion occurred due to the changes in Earth’s environments.
The seas provided environments for rapid evolution of new organisms.
Adaptations (the characteristics that species develop over time that help them survive in a particular environment) occurred.
Other organisms became extinct
Asteroids may have caused mass extinctions that gave way to rapid evolutionary changes.
The Cambrian Explosion