L01: Fossilization

SQ: What is a fossil? Is it limited to only lithification(so just things that have turned into stone)?

The preserved evidence of an organism. Any lasting trace of ancient life.

Although lithification is the most common fossil preservation, it is not limited to it as fossils can be preserved in things other than stone.

SQ: What is the difference between body and trace fossils?

Body fossil: Preserved body parts of organisms (like animals, plants, and microscopic organisms). This is literally anything that preserves the shape of an organism’s physical body shape rather than behavior—> NOT limited to bone.

Trace fossil: Preserved evidence of behavior(anything an organism does). Created on a medium(substrate), not a body part or organism(MEANING PLANTS AS WELL) that turned into a fossil.

What are different types of trace fossils?

1. Footprints and trackways

2. Burrows

3. Bite marks(pred prey behavior)

4. Gastroliths(stomach stones-helps break down vegatation)

5. Feeding traces

6. Coprolite(fossilized poop)

7. Feeding tunnels/burrows

8. “Farming” tunnels

What is a substrate?

A physical material an organism interacts with, lives on, or digs into. In short, a sediment trace was left on and can be hard or soft(affecting trace fossil shape).

By understanding diff substrate, can use that for other species

SQ: What are the strengths of body fossils?

Tells us about anatomy(like what body part had), function(can infer what it can physically do but body fossils can’t tell you what it actually did in real time), and evolution(how change over time)

Body fossils tell us the mechanical function of an individual part (e.g., this jaw was built to bite down with massive force), whereas trace fossils tell us the behavioral action of the whole animal (e.g., this animal bit into a specific prey item). The easiest way to think about it is the difference between what a machine is built to do (function) versus watching the machine actually run (movement).

SQ: What are the weaknesses of body fossils?

Body fossils cannot tell us about the movement of anatomy(like the actual movement, not inferred), or certain ecological interactions; they can’t tell us about behavior.

EX: Prey and Diet

Does not preserve soft tissue: Body fossils rarely preserve muscles, tendons, or ligaments, so can’t see how the body moved in real time

SQ: What are the strengths of trace fossils? What do trackways tell you?

Tell us about movement and dynamic(how did the body part move?), gives evidence of how animals are like behavior wise.

Trackways tell us about how the organism walked, crawled, ran, or swam

SQ: What are the weaknesses of trace fossils?

Very easy to misinterpret.

Many different traces are produced by the same individual/species

Many similar traces are produced by different individuals/species

What 3 things is a trace fossil the result/product of?

Result/product of movement(dynamics)(ex, can change is holding something), substrate(diff trace left in soft/hard ground), and anatomy(3 toed thing leaves specific print) in addition to preservation

Trace fossils: What can footprints and trackways tell us, movement wise?

Walking/running speed, walking/running mechanics, posture, complex locomotion(physical ability of an organism to move through its environment).

Can also tell you about landing behaviors and how many limbs the animal walked on.

Also, based on the weight distribution of the foot print, can tell how someone walked(like heel or ball first?)

What does Alexander’s formula estimate? What are the two(teco three) things that add up to the result?

Walking/running speed

Footprints(size and look) and trackaways + leg lengths = walking/running speeds

Trace fossils: What can bit marks and feeding traces tell you?

Feeding motion

SQ: Can a fossil be simultaneously a body and trace fossil?

YESS! Not mutually exclusive aka can be BOTH. Ex in the slides: velociraptor toe claw lodged in protoceratops neck. This has both bc the bone is preserved and bite marks(shows predator-prey behavior, how to use claws to attack, and defense/struggle techniques from the prey).

Gnathostomata

Vertebrates with jaws(very special)

What are living fossils? Are they fossils?

Living organisms that are very closely resemble their fossil relatives

There is very little change in external anatomy (in terms of evolution)

NOT fossils.

SQ: What are the 3 categories of rock(grouped together by how they form)?

Igneous, sedimentary, metamorphic

Igneous Rocks

Formed from the cooling and solidifying of molten rock (magma underground or lava on the surface)

Sedimentary Rocks

Formed when loose pieces of eroded sand, pebbles, shells, and other materials pile up in layers and get squeezed and cemented together over time.

Metamorphic Rocks

Formed when existing igneous or sedimentary rocks are changed deep underground by intense heat and pressure w/o fully melting

SQ: In which category do most fossils belong? Why don’t they belong in the other categories?

Sedimentary

Organisms remains are typically destroyed before becoming igneous or metamorphic rock(bc the process to turn it into said rock is too intense), so sedimentary rock will only keep fossils preserved!

How do lithified fossils form? What are some traits of lithified fossils?

Via erosion and lithification, same process that form sedimentary rock. It’s erosion first, bc fragments so loose rock, then lithification(loose sediment—>sed rock) to turn into a solid sedimentary rock

Traits: Fossils preserved as rocks, the most common type of fossils, typically sedimentary.

The rock cycle

Process by which rocks of one type are transformed into another type(how fossils form)

What are the processes that turn each rock into the other? In other words, what is A, B, and C?

A- Melting and solidification

B- Heat and Pressure

C- Erosion and litification

What are the two types of weathering? Give a brief description of both

Mechanical Weathering- Rocks physically reduced to smaller pieces(grains) and transported by water, wind, and gravity. So something literally makes the rock chip

Chemical Weathering- Rocks dissolved(in like water, gases, and acids) by and become suspended as mineral ions in water, gases, and acids.

What are the two steps of the formation of sedimentary rock? Can you describe the general formation of it?

1. Weathering

2. Lithification

Basc, mechanical weathering makes small rocks and it gets transported, deposited, and compacted somewhere, then chemical weathering of the rock brings minerals ions in the water, these mineral ions + water complex interacts with the rock pieces, and binds all the loose rock particles, via crystals formation, over time to make sedimentary rock.

What is lithification? How does that promote sedimentary rock formation, aka, what are the steps?

Becoming a single unified piece of rock.

1. Deposition of mechanically eroded grains(rock pieces). Deposited sediments have large spaces b/t grains.

2. Compaction of pore spaces from burial as the weight of overlying sediment results in compaction, reducing space b/t grains so less cement(water+ion) is needed to glue pieces together.

3. Cementation between grains fuses them into a single piece of rock. Water + mineral ions flows b/t grains, filling spaces with mineral precipitate that cements grains together(mineral ions grow over repeated washing w/ water as the water brings a little bit to the gaps each time). Ex: carbonates, silicates, and iron oxides.

This all takes a very long time.

What is this cement that keeps being mentioned?

Mineral ions precipitate out of aqueous solution forming microscopic crystals that adheres (“glues) the grains together. Aka, rock crystals.

SQ: How do fossils form as molds and imprints? Describe both way.

Two ways: External mold/imprint and internal mold/imprint

External:

• The sediment around the organism is cemented together (lithified) into a single, unified rock.

• Whole organism decays leaving a void.

• Preserves outer shape and texture of the organism(what the outside looks like).

• Smaller rock particles, more detailed footprint/shells

• Kellie desc: void left around rock particles, water and mineral ions wash over the sediments, creates cement, solidifying the rock outside the void and then leaving a mold.

Internal:

• Sediments fills the space/cavity inside the organism and is lithified(turned into a rock)

• Whole organism decays, revealing the sedimentary rock inside

• Preserves internal shape and texture of the organism

• So water and ions go inside the sediment fills organism and solidifies the outside.

These molds and imprints are the same as the surrounding rock

SQ: How do fossils form via permineralization(“pore” mineralization)?

• Pore spaces and cavities within and between cells(tissues) are invaded by water containing dissolved mineral ions

• Mineral ions precipitate in the spaces, filling them with mineral crystals

• Possible for organice structure(like bone), to be preserved, broken stuff easier to preserve

Kellie desc: Water and mineral ions fill the inside of the tissues—>all pores filled in anywhere water can go—> tissue turns into rock as all pores are hard with crystals.

Like sedimentary but cement is filling the inside of the tissue!

SQ: How do fossils form via replacement?

• Organic minerals(like bone and tissue) are dissolved by water as soft-tissues decay slowly

• New mineral precipitates(goes into organic thing) as original organic mineral dissolve, taking its place

• Dissolved mineral ions originate from the surrounding rocks or recycled from the original organic material

Kellie Desc: Water erodes bone minerals/tissues while depositing it’s minerals from og rock or other rock at the same time. Water takes bone materials away with it when it washes over the bone and replaces them with minerals water brings with it.

Permineralization vs. Replacement

Difference is that water can erode bone away, but if it doesn’t replace the actual bone minerals, than pore min. is not replacement. Water minerals grow in pores without washing any bone minerals away(permin).

SQ: How do fossils form via carbonization?

• Organic material is reduced to carbon film by heat

• Commonly occurs in organisms with high carbon content, like plants and invertebrates

• Very thin film that is 100% carbon, so the color is a dark gray residue, as it’s a leftover of heat and kept together through pressure

Kellie Desc: You bake(heat) organism molecules and pressure(to keep together)—>all volatile gases will leave the organism—>turns into fossil fuels—>leaves a dark grey residue.

SQ: Though uncommon, how do fossils form via the igneous rock process?

Preservation via pyroclastic flow

• Organism is buried in ash or pyroclastic flow(tephra) from volcanic eruption

• Ash/tephra creates a crust/casing and solidifies as it cools down, preserving organism

• Mineral precipitate fill cavity (this is via permineralization), tissue gone, crust there

Kellie Desc: Pyroclastic event—>ash—forms crust around organism—>solidifies—> preserves shape of organism—>empty cavity left—>permineralization to fill.

SQ: How do fossils of microorganisms form within the cracks of igneous rocks?

Microbial colonies fossilize by becoming encased in precipitated mineral ions(cement crystals) or via permineralization of volcanic rock.

By filling in the cavity with minerals, it preserves any microbes in it with said mineral ions.

Microorganisms (ex fungi, bacteria) form colonies inside crashs and vugs(vesicles or air prockets) of igenous rocks (they live and die in ruihole).

What are non-lithified fossils? Are they common? Give some examples.

Fossils that are preserved and NOOOOTTTT turned into rock(so no perminerization, replacement, mold..).

Instead, they are organisms preserved in amber, tar, and ice (these are the only thing that preserve the organism)

These are uncommon.

Ex: Ice, amber, tar, mummified reamins, blood vessels, and possible ancier DNA (if thousands of year old, can’t survive millions).

What is amber?

Tree resin broken down by heat

Organic origin, not considered a mineral(b/c not a rock)

Organism is covered by tree resin

Heat and pressure cause volatile oils from the tree resin to evaporate as the remaining biomolecules form bonds with each other(polymerize) and oxidize.

SQ: What are chemical biomarkers(like "body fossils)?

Sometimes referred to as molecular fossils

These are biochemical products typically produced by biological systems like proteins and lipids (ex steroids).

Ex: sea sponges. Sea sponge fossils show up around 540 MA(million years), but the chemical biomarkers provides evidence for older sponges.

SQ: How does chemical biomarkers provide evidence of past life?

Chemical biomarkers provide evidence of past life by preserving stable molecular fossils—such as modified lipids—whose complex structures and carbon isotope ratios can only be created by living organisms

Kelle Desc: Evidence of life as it’s a product of biological reaction that is unlikely to form spontaneously, as it’s so complex that we know it came from organisms with a certain biological pathway to make it.

Can track how long ago a fossil/organism is.

SQ: What is chemical fractionation(like trace fossils)? Which one do living systems favor?

Disproportionate abundance of one type of isotope due to being used by organisms.

in other words, diff propotion than what you expect in an environment(heavy and light isotopes are different than expect bc life is favoring the lighter one).

Living systems favor lighter stable isotopes in chemical reactions(less E use), meaning they use more light isotopes to carry out rxns in env.

How do you measure chemical fractionation(simple way as complex is with a bunch of devices)? What heavy/life proportion do you expect for living and dying organisms?

You measure the env. the organism was on, not the actual isotopes in the organism (b/c there may not be anything to extract).

that’s why it’s a trace, bc you are getting the isotopes it left behind

Living- less light than heavy bc org uses light for chemical rxn

Dying- more light than heavy bc the light isotopes in it’s body is thrown up all over that spot.

SQ: How does chemical fractionation provide evidence of past life?

Living organisms preferentially use lighter isotopes of elements (like Carbon-12 over Carbon-13) in their metabolic processes. This leaves behind a distinct chemical signature in organic matter and rocks that differs from purely non-biological, inorganic chemical reactions.

Also, there will be a different proportion of what you expect of heavy and light isotopes in an env, telling you past life was there.

What is geobiology?

Study of microbe-geology interactions (how interaction take place)

Preserved evidence of microbial life

• Specifically, the interaction between microbiota and rocks

• Ex:stromatolites

What is a stromatolite?

• Complex colony of bacteria and archea

• Cyanobacteria colony living on the surface, forms layers as they are covered by sediment

• Archea and other bacteria within the stromalite decompose prevous colonies

• Oldest record dates back to 3.7 Ga(Giga annum=billion years ago)