The Precambrian-Cambrian (Transitioning) Flashcards
What happened as the Precambrian eon ended to start and throughout the Cambrian eon?
Microbial mats DECREASE
Bioturbation (disturbance of sedimentary deposits by living organisms) INCREASES
DIVERSITY GREATLY INCREASES
Animals soon realize that the microbial mats are tasty essentially eating it away, organisms begin to disrupt the sediment layers as burrowing increases
Predators soon start to eat other things
TOOK MILLIONS OF YEARS FOR THIS TO HAPPEN
What is the first era of the Phanerozoic eon?
PALEOZOIC ERA
What is the Phanerozoic eon?
The eon we are in today, marks the period dominated by complex animals
What is the Paleozoic era?
Old animals
What is the Cambrian period? When?
The first explosion of animals, emergence of complex animals
Occurred around 542 million years ago?
What were the first shelled animals?
Cloudina
Major Proterozoic (Precambrian) and Phanerozoic (Cambrian) events recorded in Death Valley (Oldest to Youngest)
Proterozoic
- Craton
- Snowball Earth Ice Age (Kingston Peak)
- Diverse Multicellular life : Ediacaran Organisms
- First Shelled Animal : Cloudina
Phanerozoic
- Cambrian explosion FIRST RECOGNIZABLE ANIMALS
What preserved small impressions of what animal? In regards to the late Proterozoic
The late Proterozoic Stirling Quartzite preserves small impressions of a tube-shaped animal
What is the tube-shaped animal that have left impressions in the Stirling quartzite?
Why are they so important?
Cloudina, marks the emergence of shells on Earth
What are drill holes? What is it an indicator of?
Drill holes are small holes on shells which are an indicator of active predation
Usually from large snails capable of drilling through seashells with their radula
Why were shells formed?
What is ironic about them?
Probably emerged as protection against predation
Even though it was for protection, it wasn’t always perfect
Predators always seem to find a way in
What lifestyle did the Cloudina have?
Cloudina considered to be a sediment sticker
The animal (its shell) would have sat upright embedded within a seafloor microbial mat
What is similar about Cloudina and Ediacaran organisms?
Their lifestyle of sediment stickers since the Edicaran organisms also lived embedded with mats
Many types lived stationary, rooted in place
What is the span of the early Cambrian?
542-509 million years ago
What marks the Precambrian-Cambrian boundary?
Marked by the first occurrence of TREPTICHNUS PEDUM (a specific trace fossil)
What does the Cambrian introduce regarding the behaviors of animals?
Marks the first occurrence of vertical burrowing and complex behaviors
What is the difference of burrow behavior between Precambrian and Cambrian organisms?
Precambrian = HORIZONTAL burrows
Cambrian = VERTICAL burrows
What is so special about the trace fossil Treptichnus pedum?
First trace fossil to incorporate a significant vertical component
Records several probes deep into the seafloor
What did organisms in the Cambrian do that Precambrian organisms (Proterozoic) did not do?
Organisms from the Cambrian would have increased bioturbation (mixing of sediment) through their burrowing activity
What does bioturbation do to sedimentary structures?
IT DESTROYS THEM
How is bioturbation measured?
Using a semi-quantitative scale called the ICHNOFABRIC INDEX (ii)
THE ii ALLOWS FOR MEASURMENTS OF BIOTURBATION
How much did bioturbation increase with the introduction of Cambrian organisms?
With the Cambrian, bioturbation increases SIGNIFICANTLY
ii rises from a 1 to a 3 DURING THE CAMBRIAN
Does bioturbation increase past the Cambrian?
YES, past the Cambrian into the Ordovician period, bioturbation would increase further to a 5
THESE LEVELS PERSIST FOR MUCH OF LATER HISTORY
What does the Cambrian mark regarding the seafloor transitioning from the Precambrian??
MARKS A TRANSITION FROM MICROBIAL MAT-COVERED SEAFLOORS TO BIOTURBATED SEAFLOORS
What happened to microbial mats during the Cambrian?
MOST Microbial mats are GONE by the END of the Cambrian
BIOTURBATION and GRAZING from animals begin to consume and destroy existing microbial mats
Are there microbial mats here today?
There are few surviving stromatolite structures in the world
Ex. Western Australia because of its unique climate
What happens to the Stromatolite diversity through time?
Stromatolite diversity is VERY HIGH during the PRECAMBRIAN
When ANIMALS ARE PRESENT, stromatolites DECLINE
(start of the Cambrian)
