1C2 The Geological Timescale and Geological Record Flashcards
Outline the geological timescale and geological records.
What does the term ‘geologic time’ represent?
The 4.6 billion years since the Earth formed.
Geologic time is represented through rock strata, which are layers of rock that have formed over millions of years.
These layers record Earth’s history, with each stratum containing fossils and minerals that provide clues about the conditions and life forms that existed when the layer was formed.
What is the geologic time scale?
A system that organizes Earth’s history into different time periods based on the study of rock layers and the fossils within them.
The geologic time scale includes eons, eras, periods, and epochs, reflecting major changes in Earth’s history.
How do scientists organize Earth’s history?
- Using the geological time scale, which divides time into eons, eras, periods, epochs, and ages.
- By analysing fossils, rock layers, and their positions relative to each other.
What is stratigraphy?
The study of rock layers (strata) to learn about Earth’s history.
Stratigraphy involves analyzing the sequence, distribution, and age of rock layers.
What is relative age dating?
Determining the age of rock layers and fossils based on their position.
Relative age dating uses principles such as superposition, where younger layers are deposited on top of older ones.
What is absolute age dating?
A method used to determine the exact age of a rock, fossil, or geological event in years.
Radiometric dating is generally used for absolute age dating. It measures the decay of radioactive isotopes to determine the exact age of a rock.
What did Aristotle propose around 350 B.C. in terms of understanding gradual geological processes?
That land and water locations could change over extremely long periods.
Aristotle’s observations laid the foundation for understanding gradual geological processes.
Who is known for observing changes in rocks and formations in the early 1000s?
Ibn Sina (Avicenna)
Avicenna, a Persian polymath, made significant contributions to geology and the understanding of rock formations.
What did Danish scientist Nicolas Steno recognize in the mid 1600’s?
That rock layers are laid down horizontally and form in chronological order.
Steno’s principles, such as original horizontality and superposition, are fundamental to stratigraphy.
What principle did geologist Charles Lyell propose in the mid 1800’s?
The principle of uniformitarianism, which states that changes on Earth occur incrementally and follow patterns seen today.
Lyell’s work emphasized that current geological processes are key to understanding the past.
In terms of geological time, what does the symbol ‘a’ represent?
Annus
(or year)
This symbol is often used in scientific contexts to denote time periods in years.
What does ‘Ma’ stand for?
1,000,000 years
(or 10^6)
Ma’ stands for “megaannum,” a unit of time equal to one million years.
What does ‘Ga’ represent?
1,000,000,000 years
(or 10^9)
‘Ga’ stands for “gigaannum,” a unit of time equal to one billion years.
What are the largest divisions of the geologic time scale?
Eons
Eons represent the broadest time intervals and include the Hadean, Archean, Proterozoic, and Phanerozoic.
How are eras defined within the geologic time scale?
Eras span hundreds of millions of years and are subdivisions of eons.
Each era is marked by significant geological and biological events, such as mass extinctions.
What are periods in the geologic time scale?
Subdivisions within eras that span tens of millions of years.
A period lasts tens of millions of years, which is the time it takes to form one type of rock system.
What are epochs?
Smaller subdivisions within periods, spanning several millions of years.
Epochs are the smallest units of geologic time and provide detailed records of Earth’s history.
What is the current geologic time division?
The Holocene Epoch within the Quaternary Period of the Cenozoic Era.
The Holocene began approximately 11,700 years ago and continues to the present day.
What are the epochs of the Quaternary Period?
- The Pleistocene Epoch
- The Holocene Epoch
The Quaternary Period is known for glaciations and the development of human civilizations.
What are the oldest three eons?
- Hadean
- Archean
- Proterozoic
These eons cover the earliest part of Earth’s history, from the formation of the planet to the emergence of complex life.
What is the current eon?
The Phanerozoic Eon.
The Phanerozoic Eon includes the current era and spans from approximately 542 million years ago to the present.
What marks the end of the Precambrian time?
It is marked by the Cambrian Explosion, when many types of hard-shelled organisms first appeared in the fossil record (about 542 million years ago).
The Precambrian time encompasses the Hadean, Archean, and Proterozoic eons.
What is the oldest era of the Phanerozoic Eon?
The Paleozoic Era.
The Paleozoic Era lasted from about 542 to 252 million years ago and saw the rise of early life forms.
What era is known as the age of reptiles?
The Mesozoic Era.
This era, from 252 to 66 million years ago, is famous for the dominance of dinosaurs.
What era includes the present time and is known for the age of mammals?
The Cenozoic Era.
This era began 66 million years ago and continues to the present, marked by the rise of mammals.
What are the periods of the Cenozoic Era?
- The Paleogene
- Neogene
- Quaternary
These periods reflect major evolutionary and climatic changes.
What epochs are in the Paleogene Period?
- Paleocene
- Eocene
- Oligocene
The Paleogene Period saw significant mammalian evolution and diversification.
What epochs are in the Neogene Period?
- Miocene
- Pliocene
The Neogene Period is marked by the development of modern mammals and early hominins.
What epochs are in the Quaternary Period?
- Pleistocene
- Holocene
The Quaternary Period is characterized by repeated glaciations and the rise of human civilizations.
What marks the ends and beginnings of eras, periods, and epochs within the Phanerozoic Eon?
Extinction events and the appearance of new species in the fossil record.
What is the geologic record?
- A standard time scale that partitions Earth’s history into four eons and their subdivisions of eras, periods, and epochs.
- This history of Earth is preserved in layers of rock and sediment.
The geologic record provides a framework for understanding the sequence and timing of geological and biological events.
Name the four eons of the geologic record.
- Hadean
- Archean
- Proterozoic
- Phanerozoic
These eons represent the major divisions of Earth’s history.
When did the Hadean eon occur?
From the origin of Earth about 4.6 billion years ago to 4 billion years ago.
What characterizes the Hadean eon?
The Earth was very hot with a partially molten surface, and there were no rocks except meteorites.
This eon saw the formation of Earth’s initial crust and the beginning of the cooling process.
When did the Archean eon take place?
From 4 billion years ago to 2.5 billion years ago.
The Archean Eon saw the formation of the first stable continental crust and the emergence of life.
What was significant about the Archean eon?
- The Earth’s surface cooled, forming continental plates and rocks, and the first prokaryotic life (bacteria) appeared.
- There was no atmospheric oxygen, but when early cyanobacteria formed they began to produce oxygen.
The Archean Eon is crucial for understanding the early development of Earth’s geology and biosphere.
What type of atmosphere did Earth have during the Archean eon?
The early atmosphere lacked oxygen and was rich in methane, ammonia, and other gases (most of which are toxic to todays life-forms).
When did the Proterozoic eon occur?
From 2.5 billion years ago to 542 million years ago.
The Proterozoic Eon saw significant geological, climatic, and biological developments, including the rise of oxygen levels.
What major changes happened during the Proterozoic eon?
Increase in atmospheric oxygen, appearance of eukaryotic cells, algae, and soft-bodied invertebrates.
This eon includes the Great Oxygenation Event and the evolution of complex life forms.
When did the Phanerozoic eon begin?
About 542 million years ago.
The Phanerozoic Eon is marked by an abundance of fossil evidence and the diversification of life.
What are the three eras of the Phanerozoic eon?
- Paleozoic
- Mesozoic
- Cenozoic
What life forms appeared during the Paleozoic era?
- many fungi
- plants
- animals
- vascular plants
- fish
- insects
- reptiles
- amphibians
When did the Mesozoic era start and end?
It started about 250 million years ago and ended about 65 million years ago.
The Mesozoic Era is divided into the Triassic, Jurassic, and Cretaceous periods.
What significant events occurred during the Mesozoic era?
- Evolution of dinosaurs.
- Appearance of cone-bearing plants and flowering plants.
- The extinction of dinosaurs.
What marks the beginning of the Cenozoic era?
The extinction of dinosaurs around 65 million years ago.
The Cenozoic Era is divided into the Paleogene, Neogene, and Quaternary periods.
What life forms dominate the Cenozoic era?
- mammals
- birds
- flowering plants (angiosperms)
What notable events happened during the Cenozoic era?
- The Ice Age
- appearance of primates
- the first human ancestors
What is the current epoch in the geologic time scale?
The Holocene epoch.
The Holocene Epoch has seen the development of human civilizations and significant environmental changes.
During which period did the Holocene epoch occur?
The Quaternary period.
The Quaternary Period encompasses the last 2.6 million years, including the Pleistocene and Holocene epochs.
What major divisions exist within the Phanerozoic eon?
- Eras (Paleozoic, Mesozoic, Cenozoic)
- Periods (like Cambrian, Jurassic, Neogene)
- Epochs (lasting millions to tens of millions of years)
