2.6

• What is the definition of speciation?

  Speciation is the process by which one species splits into two or more species.
• How does speciation contribute to biodiversity on Earth?

  It explains how new organisms arise from pre-existing ones, contributing to the diversity of life.
• What does the biological species concept define?

  A species is defined as a group of populations whose members can potentially interbreed and produce fertile, viable offspring.
• What is the morphological species concept based on?


  It groups organisms as separate species based on similarities in their morphology or body structure.
• How does the ecological species concept classify organisms?

  It groups organisms as separate species based on their ecological niche or role in the ecosystem.
• What is the phylogenetic species concept?

  It groups organisms as separate species if they form one branch in the tree of life.
• What is allopatric speciation?

  Allopatric speciation occurs when two groups of organisms are separated by geographic barriers that prevent gene flow.
• What is sympatric speciation?

  Sympatric speciation occurs when two groups separate into two species while living in the same geographical area.
• What is the geologic time scale?

  The geologic time scale is a record of Earth's history built by geologists through paleontology.
• How is the geologic time scale divided?

  It is divided into three eons, with the third eon characterized by major evolutionary events in the animal kingdom.
• When did the first single-celled organisms exist?

  They existed about 3.5 billion years ago.
• What are stromatolites?


  Stromatolites are layered rocks that form when certain prokaryotes bind thin films of sediment together.
• When did the first photosynthetic organisms appear?

  They appeared around 2.7 billion years ago.
• What evidence supports the appearance of the first photosynthetic organisms?

  The presence of iron-rusted rocks dated around 2.7 billion years ago supports this evidence.
• What was the impact of increased oxygen concentration in the atmosphere?

  It caused a wave of extinction among anaerobic single-celled organisms and favored survivors that adapted to aerobic cellular respiration.
• When did the first eukaryotic organisms appear?

  They appeared around 2.1 billion years ago.
• What does the endosymbiotic theory describe?


  It describes how organelles of eukaryotes, such as mitochondria and plastids, were once engulfed prokaryotes that lived inside eukaryotic cells.
• When did the earliest ancestors of multicellular eukaryotes appear?

  They appeared approximately 1.2 billion years ago.
• What is the significance of the Ediacaran Biota?

  It supports the diversification of multicellular eukaryotes into larger and more complex forms around 575 million years ago.
• When did the Cambrian explosion occur?

  It occurred around 535-525 million years ago.
• What characterizes the Cambrian explosion?

  It is characterized by the evolution and appearance of many animal groups such as poriferans, cnidarians, and molluscs.
• When did large forms of life begin exploring land?

  They began exploring land around 500 million years ago.
• What challenges did life face when colonizing land?

  Challenges included ease and efficiency of reproduction and the threat of desiccation or dehydration.
• What adaptations did plants develop for land colonization?

  Adaptations include the presence of a cuticle or waxy layer and vascular tissues.
• Which animals were the first to colonize land?

  Arthropods were the first animals to colonize the land, approximately 420 million years ago.
• When did humans diverge from primate ancestors?

  Humans first diverged from primate ancestors around 6-7 million years ago.
• When did modern humans appear?

  Modern humans appeared around 195,000 years ago.