Environmental scienceLesson 4 of 5 in the course Earth as a Planet

Early Life, Atmospheric Oxygenation, and Human-Driven Climate Change

5 flashcards · 4 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Life began early in Earth's history, but the earliest chapters of its story are difficult to reconstruct. This lesson explores the evidence scientists use to investigate life's origins and the genetic relationships that reveal the breadth of life on Earth.

The earliest record of life is incomplete because Earth's crust is continually reshaped by geological activity. Chemical evidence suggests that life was present by the time the oldest surviving rocks formed, about 3.9 billion years ago. By about 3.5 billion years ago, organisms were forming large colonies called stromatolites. Stromatolites still form in some places today.

All flashcards

What is a stromatolite?
A layered structure produced by microbial communities; similar structures still form today.
What is a genome?
An organism's complete set of DNA.
What is photosynthesis?
A process that uses sunlight to build energy-rich organic material and releases oxygen.
What is the natural greenhouse effect?
Warming caused when atmospheric gases absorb and re-emit some outgoing infrared radiation.
What does the term Anthropocene describe?
A proposed period in which human activity has become a major influence on Earth's systems.

Quiz questions

  1. Which description best characterizes Earth's early atmosphere?Answer: It had abundant carbon dioxide, some methane, and essentially no oxygen gas.
  2. Why did oxygen produced by early photosynthetic organisms take a long time to accumulate in the atmosphere?Answer: Reactions with Earth's crust consumed much of the newly produced oxygen.
  3. How did the ozone layer help organisms colonize land?Answer: It absorbed much of the Sun's harmful ultraviolet radiation.
  4. Which two processes contribute directly to rising sea levels as the climate warms?Answer: Melting land ice and expansion of warmer ocean water.

Based on Astronomy 2e by Andrew Fraknoi, David Morrison, Sidney Wolff (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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