Chapter 25 History of Life Flashcards
(38 cards)
When was the formation of Earth?
4.6 Billion years ago
What and when was the first period?
Hadean (4.8B to 4B)
What happened during Hadean? (5)
-Formation initial crust
-Formation of Moon
-Differentiation of earth layers
-Early atmosphere
-Liquid water
What and when was the second time period?
Archaean (4B to 2.5B)
What happened during Archaean?
-Geological formations
-Earths magnetic field weak and less stable
-Mostly water world
-High heat flow (volcanos and tectonic plates)
What is abiogenesis?
Processes that gave rise to life on Earth not completely understood.
What is the prevailing scientific hypothesis about the origin of life?
Transition from nonliving to living entities was not a single event but a process of increasing complexity involving.
What is LUCA?
Last Universal Common Ancestor
When and what was earliest evidence of life on Earth?
Biogenic graphite 3.7 billion-year-old rocks Western Greenland.
What and when were the first identifiable fossils on Earth?
Stromatolites (prokaryotes) 3.48 billion-year-old sandstones (living found in western Australia).
What was the Great Oxygenation Event (GOE)?
It was when photosynthesis began releasing oxygen, which reacted with dissolved iron in oceans, forming iron oxide that settled as banded iron formations (BIFs).
What happened after the iron was used up?
Oxygen started building up in oceans, and around 2.7 billion years ago, it began entering the atmosphere.
What marked the end of the Archaean era?
Around 2.5 billion years ago, atmospheric O₂ reached 1–10% of current levels, signaling the end of the Archaean.
What and when was the third time period?
Proterozoic (2.5B to 0.5B)
What major atmospheric changes occurred during the Proterozoic Era?
Oxygen buildup (“gassing out”) reduced methane, altering the climate and atmosphere. An ozone layer formed, protecting Earth from UV radiation.
What was the first major glaciation in the Proterozoic?
The Huronian glaciation (~2.4–2.1 billion years ago), possibly a “Snowball Earth” event that influenced early life evolution.
When did eukaryotic cells first appear?
Around 2 billion years ago, likely through endosymbiosis.
How did eukaryotic cells evolve from prokaryotes? (3)
- Membrane evagination formed the nucleus and endoplasmic reticulum.
- A Gram-negative bacterium was engulfed as prey or parasite.
- Over time, the host and endosymbiont became interdependent, forming the first eukaryotic cell.
When was first eukaryote fossil?
1.8B
When was first multicellular eukaryotes?
1.3B
When did the first multicellular animals (metazoans) appear? (3)
- 890 Ma: Sponge-like Porifera biomarkers
- 575 Ma: Ediacaran biota – soft-bodied, clearly multicellular fossils
- 555 Ma: Trace fossils like burrows and tracks show the appearance of mobile animals
What major changes occurred at the end of the Proterozoic? (2)
- Ocean chemistry improved: more nutrients and deep-water oxygenation.
- O₂ levels rose near modern levels, likely due to secondary endosymbiosis, supporting more complex, energy-demanding life.
What led to the extinction of Ediacaran species? (2)
- Environmental changes (e.g., Baykonur Glaciation, breakup of supercontinent Pannotia)
- Competition with emerging complex life forms
What is the fourth time period?
Phanerozoic (0.5B to Today)
