Animals: Week 1

Which era occurred 3.5 billion years ago?

Precambrian

What emerged following the Precambrian era?

Prokaryotic cells

Give two features of prokaryotic cells?

Single celled and anaerobic

What does it mean for an organism to be anaerobic?

It can survive without oxygen

What initially absorbed new oxygen, and where were they found?

Ferrous irons, found in oceans

Why did free oxygen begin accumulating in the atmosphere and what did this lead to the emergence of!

As oceanic iron sinks were saturated, leading to the emergence of eukaryotes

What was the cause behind a snowball Earth?

The clustering of continents near the equator

Give 2 reasons why the clustering of continents near the equator was the cause behind snowball earth

Due to increased rock weathering, trapped carbon and low temperatures

What is the term for the phenomenon of lighter colours reflecting sunlight and darker colours absorbing it?

The albedo effect

What percentage of sunlight did the ice reflect back during the snowball Earth era?

80-90%

Which natural process aided in the increasing temperatures of snowball Earth, and why?

Volcanic eruptions

As they slowly pumped out large volumes of carbon dioxide

Give two driving factors behind the recovery if snowball Earth?

Massive nutrient influxes

Global melting

Increased oxygen levels

Eustatic sea change

What is PAL?

Present atmospheric level of oxygen

What percentage range of PAL is required to support complex life?

6-10%

How long did the Ediacaran period last?

96.2 million years

What was the name of the first super continent?

Rodinia

Which major changes occurred during the Ediacaran era?

Eustatic sea rise

The formation of land masses

What was the result of eustatic sea rise?

The flooding of continental margins

Determine whether these statements are true or false, then correct the false statements. Ediacarans are:

Only protists and algae

Soft bodied organisms

Complex structures

A lineage

Exclusively found in ultra fine mud

False; they are a highly diverse mix of animals, protists, and algae

True

True

False; they represent an interval p, not a lineage

False; Unlike other fossils, they are only found in coarse sandstone

Give two reasons why Ediacarans are often found perfectly preserved

Microbial mats (prevented mineralisation)

The absence of burrowing animals (would have eaten the decaying organic matter)

Rapid burial

What are microbial mats?

Thick, dynamic layers of bacteria and algae that glued the seafloor together

What category if the food chain did the Ediacaran ecosystem lack?

Predators

What were the three preservation styles in the Ediacaran period?

Avalon

White Sea

Nama assemblages

Give an example of two organisms preserved in the ‘White Sea’ style

Dickinsonia and the Kimberella

How are stromatolites formed?

By the segmentation of sedimentary grains

How is the flat, oval ribbon-like body of the Dickinsonia an advantage?

It increased the maximum surface area in contact with the sea floor, absorbing more nutrients through the skin

What are the ribbed, uniquely offset segments of the Dickinsonia called?

Isomers

How is the bilateral symmetry along the central axis of the Dickinsonia an advantage?

The interlocking zigzags allowed for more fluid movement across the sea floor without the tearing of thin tissues

Give two reasons why researchers initially believed the Dickinsonia was an early stem group animal

The possible movement spotted along the seafloor

Their structural complexity

It grew new segments and expanded existing ones

It was fed by externally digesting organic matter

Chemical biomarkers

What was the shell of the Kimberella like?

Flexible

Non mineralised

Made of tough organic tissue

How is the muscular foot of the Kimberella an advantage?

It allowed the organism to propel itself

Provided the required ,ever age to scrape up food

Allowed the organism to churn through sediment if buried

Give two features of Rangeomorphs

Quilted construction of fluid-like tubes

Repeated fractal design

Lacked mouths and digestive systems

Which two ways did Rangeomorphs gain nutrients?

Osmotrophy and suspension

What is osmotrophy?

The direct absorption of dissolved organic carbon from surrounding sea water

What us suspension feeding?

The passive filtering of organic particles/micro-plankton from water currents

How did the horseshoe shaped head structure help the Spriggina, being an organism in low energy marine environments.

By acting as a miniature snowplough, allowing it to push through and over dense slime layers

Determine whether the statement is true or false, then correct the false wording. Oxygenation occurred in, localised, low functioning pulses

False; oxygenation occurred in localised, high functioning pulses

When did the Cambrian explosion begin?

Around 538 million years ago

During the Cambrian period, which two things saw an increase?

The appearance of animals with mineralised shells

Complex trace fossils

Place each stage of the movement evolution in order:

Muscular borrowing and crawling

Passive drifting

Cilia and flagella propulsion

Passive drifting

Cilia and flagella propulsion

Muscular borrowing and crawling

Give two reasons behind the disappearance of the Ediacaran biota

Environmental change

The rise of complex animals

Substrate disturbance

Changing oxygenation

Why are trace fossils more accurate than other fossils?

They provide us with a record of life processes e.g. feeding styles, locomotion, mating