The History of Life on Earth

Chapter 17

3 Types of Rock:

Igneous (volcanic), sedimentary (sand, soil), and metamorphic (rocks formed by pressure).

Fossils form in

sedimentary rocks over time through the preservation of organic material.

Principles of Stratigraphy

Methods of determining the age of sedimentary rock layers and the fossils contained within them. Younger layers are deposited on top of older, fossils appear in the same order in different outcrops.

Igneous (volcanic) rock

Contains radioisotopes that are used for dating strata and the fossils they contain.

Radiometric dating

is a technique used to date materials based on the decay rate of radioactive isotopes, providing an accurate age for rocks and fossils.

Half-life

is the time required for half of the radioactive isotopes in a sample to decay, crucial for radiometric dating of rocks and fossils.

The history of life is divided into __ which are subdivided into __.

eras; periods

Fossilization occurs only when

organisms are at sites with no oxygen and where decomposition is very slow.

Paleontologists

study fossils to understand past life forms and their environments.

Positions of the continents have changed over time due to

continental drift

Alfred Wegener

was a meteorologist and geophysicist who proposed the theory of continental drift, suggesting that continents were once connected and have since moved apart.

Plate tectonics

Geophysics of the movement of land masses and the processes associated with the Earth's lithosphere, including the formation of mountains, earthquakes, and volcanism.

Ash and SO₂ are injected into the atmosphere

during volcanic eruptions, leading to climate changes and impacts on the Earth's temperature, while resulting in cooling.

Cooling can lead to increased glaciation

leads to drops in sea-level and mass extinctions (End-Permian event)

The early life atmosphere

had little or no O_2.

Cyanobacteria formed

stromatolites which are abundant in the fossil record.

Cyanobacteria releases oxygen which

transformed the Earth's atmosphere, enabling the evolution of aerobic organisms.

Pre-cambrian era

is the earliest part of Earth's history, life consisted of microscopic prokaryotes living in oceans. By the late era, many kinds of multicellular organisms began to appear.

Cambrian period (542-488 mya)

is known for the "Cambrian Explosion," a rapid increase in the diversity of life forms, including the first appearance of many major animal groups. (evolutionary radiation)

Ordovician period (488-444 mya)

is characterized by significant marine diversification, with the first coral reefs forming and the dominance of brachiopods and mollusks. It ended with a mass extinction due to massive glaciers and lowered sea levels.

Silurian period (444-416 mya)

is noted for the stabilization of the Earth's climate and the continued evolution of fish, as well as the first terrestrial plants and insects.

Devonian period (416-359 mya)

is recognized as the "Age of Fishes," when diversified fish groups thrived, along with the first amphibians and significant advancements in plant life.

Carboniferous period (359-297 mya)

is known for the extensive formation of coal forests, the diversification of amphibians, and the evolution of early reptiles, along with significant developments in plant life.

Permian period (297-251 mya)

is characterized by the greatest mass extinction event in Earth's history, where approximately 90% of marine species and 70% of terrestrial vertebrate species became extinct, along with significant climatic changes. (Likely due to volcanic activity and temperature fluctuations).

Continents came together form

Pangaea

Siberian Traps

are massive volcanic features in Siberia that were instrumental in the Permian period's mass extinction, contributing to climate change and habitat loss.

Triassic period (251-200 mya)

follows the Permian period and is noted for the emergence of the first dinosaurs and mammals, as well as significant geological and climatic changes. Pangaea began to break apart.

Jurassic period (200-145 mya)

is known for the dominance of dinosaurs, the appearance of the first birds, and significant developments in marine life. This period also saw the further fragmentation of Pangaea into separate continents (Laurasia in the north and Gondwana in the south).

Laurasia

The northern supercontinent formed from the breakup of Pangaea.

Gondwana

was the southern supercontinent formed from the breakup of Pangaea.

Cretaceous period (145-65 mya)

is known for the continued dominance of dinosaurs, the emergence of flowering plants, and significant changes in sea levels. This period ended with a mass extinction event that wiped out many species, including the dinosaurs.

Tertiary period (65-2.6 mya)

is characterized by the rise of mammals, the development of grasslands, and significant climate changes (becoming cooler) leading to the current configuration of continents.

Quaternary period (2.6 mya to present)

“Ice Ages”, continental glaciers spread, shifting the ranges of plants and animals. Many large mammal species went extinct in Australia and the Americas during this time, while humans began to appear and evolve.