Molecular Clock and Paleontology Overview

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Questions and Answers

What was the primary early source of atmospheric oxygen?

Multicellular algae

Land plants

Eukaryotic cells

Cyanobacteria (correct)

What significant event occurred around 2 billion years ago?

The formation of banded iron formations stopped

The first eukaryotes emerged (correct)

Oxygen saturated the atmosphere

The first multicellular organisms appeared

What process led to the formation of mitochondria and plastids in eukaryotic cells?

Gene transfer

Cell differentiation

Spontaneous generation

Endosymbiosis (correct)

What type of cellular structure is formed from the infolding of the plasma membrane?

Nuclear membrane Signup and view all the answers

Which of the following is true about the oldest known multicellular eukaryotes?

They first appeared around 1.5 billion years ago. Signup and view all the answers

What characteristic is shared by all animals according to the information provided?

Homeobox genes Signup and view all the answers

During which period did the Cambrian explosion occur?

Paleozoic Signup and view all the answers

Which of the following is considered a derived character of chordates?

Notochord Signup and view all the answers

What does the expression pattern of Hox genes along the chromosome correlate with?

The position of expression along the body axis Signup and view all the answers

Which organism is mentioned as a Cambrian relative to vertebrates?

Pikaia Signup and view all the answers

What significant interaction is evidenced by fossils from the Cambrian explosion?

Predator-prey interactions Signup and view all the answers

Which type of fossils are described as being difficult to categorize as either animals or algae?

Ediacaran fossils Signup and view all the answers

What best characterizes the sudden appearance of fossils during the Cambrian explosion?

Emergence of modern animal phyla Signup and view all the answers

What is the molecular clock primarily used to measure?

Rate of mutation in DNA Signup and view all the answers

Which method is used for absolute dating of fossils?

Radiometric dating Signup and view all the answers

What does the principle of superposition state?

Older layers are found below younger layers. Signup and view all the answers

Which of the following methods can be used for dating volcanic rock?

Argon-Argon dating Signup and view all the answers

Which ape split is estimated to have occurred around 6-8 million years ago?

Human and chimpanzee Signup and view all the answers

What kind of fossils are preserved mineralized parts of organisms such as teeth and bones categorized as?

Body fossils Signup and view all the answers

What is the basis for radiometric dating methods?

Half-life of radioactive isotopes Signup and view all the answers

How is the molecular clock calibrated?

Using fossil records and mutation rates Signup and view all the answers

What characterizes the normal rate of extinction compared to mass extinctions?

Slower and more gradual process Signup and view all the answers

Which event is considered part of the Big 5 mass extinctions?

The extinction of dinosaurs Signup and view all the answers

What is the current estimated rate of extinction compared to background extinction levels?

100-1000 times larger Signup and view all the answers

What was the primary composition of the first cellular life forms on Earth?

Prokaryotic autotrophs Signup and view all the answers

What has been one of the significant impacts of plate tectonics on biodiversity?

Facilitates the spread of species across continents Signup and view all the answers

Which of the following organisms thrived in the ancient Earth atmosphere prior to saturation with oxygen?

Photosynthetic cyanobacteria Signup and view all the answers

What role do chemoautotrophs play in ecosystems?

They convert simple compounds into organic matter. Signup and view all the answers

What are stromatolites primarily composed of?

Photosynthetic cyanobacteria and sediments Signup and view all the answers

Study Notes

Molecular Clock

Some parts of the genome accumulate changes (mutations) at a relatively steady rate.
The speed of accumulation depends on the part of DNA under study (some fast, some slow).
The “clock” is calibrated using the fossil record (e.g. orangutan fossils have been securely dated for apes), or the accumulation of mutations over generations.
Using the known age of the orangutan split, plus info on orangutan DNA, we know the rate of mutations in certain parts of the ape genome.
Count known differences in DNA between humans and chimps.
The data indicates a date of the split between Pan and Homo at about 6-8 million years ago.

Paleontology: Scientific study of fossil organisms

Fossils are preserved mineralized parts of organisms (shells, teeth, bone).
Trace fossils left by organisms (indirect evidence).
Coprolites and other remains.
More rarely: soft parts preserved as minerals.

Paleontology: Dating fossils

Relative dating: Principle of superposition; any layer of sedimentary rocks is older than the layer above it and younger than layers below it.
Absolute dating (chronometric): Radiometric dating.
Uranium series dating (U-Series): 238U turns to lead (Pb) – Series of half-lives (several isotopes, 100 000s to billions yrs).
Argon-Argon (40Ar-39Ar) dating is often used on volcanic rock - 1.25 billion year half-life.

Patterns of Extinctions

Background Extinctions: “Normal” slow rate of extinction; 96% of extinctions.
Mass Extinctions: Global extent; Broad range of species; Often rapid.
Five major mass extinctions: Some mark the ends of geologic eras.
6th Mass Extinction? 1,100 species extinct since 1600.
Habitat loss, hunting, introduction of non-native species.
Previous mass extinctions took at least 5 million years to recover species diversity.
The current rate of extinction is 100-1000X larger than background extinction.

Plate Tectonics and Continental Drift

Movement of continents (Pangea 250 million years ago).
Formation of mountain ranges, leading to movement and separation of species.
Can also explain some changes in climate.

3.5 Billion Years Ago: First Evidence of Cellular Life

The oldest known fossils are stromatolites, geological structures composed of many layers of photosynthetic cyanobacteria and sediment.
Date back to 3.5 billion years ago.
Prokaryotes were Earth’s sole inhabitants from 3.5 - 2.5 billion years ago.
Prokaryotes typically have a cell wall outside the phospholipid plasma membrane.

2.5 Billion Years Ago: Atmosphere Becomes Saturated With Oxygen

Atmospheric oxygen (O2) is of biological origin.
The early source of O2 was likely cyanobacteria.
O2 produced by photosynthesis reacted with dissolved iron and precipitated out to form banded iron formations.

Ca 2 Billion Years Ago: First Eukaryotes

Oldest eukaryote cells ca 2 billion years ago.
Related to archaeans.
Nuclear membrane formed from infolding of plasma membrane.
Endosymbiosis: mitochondria and plastids (chloroplasts) were formerly small prokaryotes – engulfed by a host cell.
Mitochondria and plastids have their own DNA and replicate in a way similar to bacteria.

1.5 Billion Years Ago: Multicellular Eukaryotes

Oldest known fossils of multicellular eukaryotes are tiny multicellular algae from around 1.5 billion years ago.
More diverse multicellular organisms do not occur until around 600 million years ago (Precambrian).

Early Animals

Enigmatic Precambrian (Ediacaran) fossils: some are hard to identify as either animals or algae.
Some are definitely the earliest animals, ca 600 million years ago (no vertebrates).

Animals

Earliest animals ca 600 million years ago, implying a peculiar genetic mechanism evolved by then.
Homeotic genes containing a highly conserved 180-nucleotide “homeobox” are called Hox genes.
Hox genes code for the body axis position in very different animals.
The position of Hox genes along the chromosome is the same as the position of expression along the body axis.

Paleozoic Starts ~550 Million Years Ago: Cambrian Explosion

Many modern animal phyla suddenly appear in the Cambrian.
Most of life is still in the seas, but some plants and invertebrates are found on land shortly after.

Paleozoic Era (550-250 mya)

Starts with the Cambrian “explosion” ca 550 mya.
First fossil chordates and vertebrates.
Best preserved in Burgess Shale, Canada.

Cambrian Explosion

Sudden appearance of fossils resembling modern phyla.
Provides the first evidence of predator-prey interactions.
More armor (shells, spikes).

Chordates

Chordates form a monophyletic taxon, with vertebrates being the most numerous group.
Chordate shared derived characters: notochord, myotomes, and others.

Cambrian Relatives of the Vertebrates: Ancient Chordates

Chordates similar to the lancelet are known from the Cambrian 530 million years ago, Burgess Shale and China.
These have the typical chordate features e.g. notochord, myotomes.

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Description

Explore the concept of the molecular clock and its role in dating the evolutionary split between humans and chimps. This quiz also covers fundamental principles in paleontology, including the study of fossils, trace fossils, and methods of dating. Test your understanding of how genetic mutations and fossil records contribute to our knowledge of evolutionary biology.