History of Life on Earth and Geological Timescale

Flashcards covering the history of life, oxygenation, mass extinctions, the Cambrian Explosion, and fossil dating methods.

What is the estimated age of the Earth?

The Earth is estimated to be roughly $4.6$ billion years old.

When is life believed to have begun on Earth?

Life began approximately $3.5$ billion years ago ($bya$).

What were the characteristics of the first organisms that emerged on Earth?

The first organisms were single-celled, anaerobic organisms.

What sources contributed to the formation of liquid water on Earth?

Water was part of the dust that formed the earth, and other sources included asteroids and meteors.

What is the 'great oxidation event'?

A period where the levels of atmospheric oxygen increased drastically due to the evolution of photosynthetic bacteria.

What does the term 'mya' stand for in geological terminology?

It stands for 'millions of years ago'.

What occurred during the Cambrian Explosion between $541$ and $530$ million years ago?

A period of rapid diversification of life, particularly animal life, where many modern animal groups first appeared.

What are three key environmental changes required for the Cambrian Explosion to occur?

Rising oxygen levels, changes in ocean chemistry (calcium and carbonates becoming available), and an increased nutrient supply of phosphorous, nitrogen, and trace metals.

What is 'cephalization'?

Concentrated nervous tissue or the development of a head in animals.

What defines a mass extinction event?

An event where over $75\%$ of Earth's species vanish over a few million years, causing a crash in biodiversity.

What is an 'impact winter'?

A period where sunlight is blocked by dust and ash from an asteroid impact, causing plant and animal life to die due to a lack of food and light.

Which toxic gases are released during major volcanic eruptions that contribute to climate change?

Sulfur dioxide ($SO_2$) and carbon dioxide ($CO_2$).

What is 'oceanic anoxia'?

A condition where the ocean's dissolved oxygen levels become severely depleted, often due to ocean warming.

When did the most severe mass extinction (the third extinction) occur, and what percentage of species died?

It occurred at the end of the Permian period, $251$ million years ago, and $96\%$ of living species went extinct.

What caused the fifth mass extinction at the end of the Cretaceous period ($65$ million years ago)?

A meteor impact in the Gulf of Mexico.

What is the primary cause of the ongoing sixth mass extinction?

Human activity, including urbanization, agriculture, pollution, and the burning of fossil fuels.

What is 'petrification' in the fossilization process?

The process where dissolved minerals carried by water replace the organic material trapped inside rock.

What is the difference between a mold and a cast fossil?

A mold is an impression or cavity left by a decaying organism, while a cast is a three-dimensional replica formed when a mold is filled with minerals.

What are trace fossils?

Geological records of the activities and behaviors of past life, such as footprints, burrows, nests, or coprolites (fossilized feces).

How does relative dating determine the age of a fossil?

By comparing its position in the earth's crustal layers (stratification), where fossils in higher levels are younger and those in lower levels are older.

What is the half-life of Carbon-14 ($^{14}C$) used in radiometric dating?

The half-life of carbon-14 is $50,000$ years.