History of Earth

stratigraphy

The method of reading the order of layers of rock

Superposition

younger rock layers sit on top of older layers; older rocks are on the bottom.

Original Horizontality

 layers of sedimentary rock are originally deposited flat or horizontally under the action of gravity and can later be deformed.

Lateral Continuity

layers are continuous until they encounter solid bodies that block their deposition or until they are acted upon by agents that appeared after deposition took place such as erosion and fault movements.

Cross-Cutting Relationship

any geologic feature that cuts across another geologic feature is younger.

Unconformities

• are geological features that represents gaps in the rock record, indicating periods of erosion or non-deposition. 

Angular unconformity

•  are originally-deposited horizontal layers that are folded or titled and then eroded. When erosion stops, a new horizontal layer is deposited on top of the titled layer, forming an angular boundary between the older tilted rocks and the younger horizontal layers.

Nonconformities

• are metamorphic or igneous rocks in a contact with sedimentary layers indicated a period of uplift and erosion of previous rocks, prior to the deposition of a younger sedimentary rock.

Disconformities

• are layers of sediments that are uplifted without folding but are exposed to weathering and erosion, producing an irregular surface. Eventually, the layer subsides and deposition resumes, forming an irregular boundary between the older and younger layers. This type of unconformity indicates a large time gap between the two layers.

Fossils

are preserved remains of plants and animals whose bodies were buried in sediments.

 Body fossils

 represent all or part of the organism's body (fossil typ0e

trace fossils

• show evidence of the organism’s behaviour. (type of fossil)

Petrification

•  is when the mineral entirely replaces the organic material, and the remains are turned into stone.

Compression

•  is when dark imprints of the fossil are produced as a result of high-pressure forces exerted by the weight of overlying sediments and sea water.

Moulds

is when a space is left behind in the shape of an original material called a

cast

•  is a positive impression of the original material formed by contact with the mould.

Index fossils

• are the remains of once-living organisms that are particularly useful for dating and correlating the age of rocks. These fossils are distinctive, widespread, and existed for a relatively short period in geologic time. The key characteristic of index fossils is that they are associated with a specific time interval, making them reliable markers for dating rocks.
  
  should have a widespread distribution. Index fossils should be found in different locations around the world. Index fossils should have existed for a short geologic range in Earth’s history. Index fossils should be relatively abundant in the rock layers where they are found. Index fossils should possess a distinctive morphology.

Nicolaus Steno

Father of Stratigraphy

James Hutton

• realized geologic processes are slow and his ideas on uniformitarianism provided a basis for interpreting rocks of the Earth using scientific principles.

Age

(millions of years)

Epoch

(tens of millions of years)

Period

(one hundred million years)

Era

(several hundred million years)

 Eon

(half a billion years or more)

Hadean Eon

- Represents the earth’s time of formation.

- No rocks are represented.

- “Hellish” conditions. Was very hot, now the earth has cooled down so we can survive on it.

Archean Eon

- Single-cell life developed.

- Most “ancient” rocks found.

- Preserved rocks at the base of the Archean.

Proterozoic Eon

- Multi-celled, soft body organisms.

- Cyanobacteria begin producing free oxygen (photosynthesis) – engulfed by the chloroplast. (Leading to the Great Oxidation Event)

- Land masses gather to make up a continent called “Rodinia.”

Phanerozoic Eon

[542 million years ago - present]

Paleozoic Era

[542 - 251 million years ago]

Cambrian Period

- Explosion of life (Cambrian Explosion)
- Dominant animals: Marine invertebrates (trilobites and brachiopods)

- Supercontinent Gondwana forms near the South Pole.

Ordovician Period

- The first animals with bones appear.

- A very cold time in Earth’s history: there was a great extinction due to ice caps in present-day Africa.

Silurian Period

- First land plants appear, and land animals follow.

- Coral reefs expand and land plants begin to colonize barren land.

- First millipede fossils and sea scorpions (Eurypeptides).

Devonian Period

- Pre-Pangea forms.

- Dominant animal: fish.

- Amphibians, evergreens, and ferns appear.

Mississippian Period

- First seed plants appear; bryophytes

- Much of North America is covered by shallow seas and sea life flourishes (bryoza, brachiopods, blastoids).

Pennsylvanian Period

- Lizards and winged insects first appear.

- Both the Mississipian and Pennsylvanian form the Carboniferous period.

Permian Period

- Last period of the Paleozoic.

- Pangea forms and the Appalachians rise.

- 90% of Earth’s species become extinct due to volcanism in Siberia.

- Permian extinction (The Great Dying).

Mesozoic Era

[251 - 65.5 million years ago]

Triassic Period

- First dinosaurs appear.

- First mammals – small rodents appear.

- Life and fauna re-diversify.

- Rocky Mountains form.

- Pangea begins to break apart.

Jurassic Period

- Pangea is still breaking apart.

- Dinosaurs flourish in the “Golden Age of Dinosaurs.”

- First birds appear (archaeopteryx)

Cretaceous Period

 T-Rex develops.

- First snakes and primates appear.

- Angiosperms appear.

- Mass extinction marks the end of the Mesozoic Era, with the demise of dinosaurs and 25% of all marine life. (era when the dinosaur-killing asteroid struck the Earth)

Cenozoic Era

[66.5 million years ago - present]

Tertiary Period

Contains poleocene, Eoncene,Oligocene,Miocene, and Pliocene

Paleocene Epoch

- First horses appear (size of cat) and tropical plants dominate.

Eocene Epoch

- Grasses spread and whales, rhinos, elephants, and other large mammals develop.

Oligocene Epoch

- Dogs, cats, and apes appear.

Miocene Epoch

- Horses, mastodons, camels, and tigers roam free in S.C.

Pliocene Epoch

- Hominids develop and the Grand Canyon forms.

Quaternary Period

Contains Pleistocene Epoch and Holocene Epoch

Pleistocene Epoch

- Modern humans develop and ice sheets are predominant
- Ice age.

Holocene Epoch

- Holocene humans flourish; beaches and barrier islands form

Anthropocene Epoch

- Not yet widely recognized

- Climate change

- Drying of rivers, melting of glaciers

Mass extinction

events occur when many living things go extinct at the same time (Impacts plants and animals on land and in the sea). Only happened twice in Earth’s history.