Description
Concepts
Learning Objectives
How To Demonstrate
Questions To Ask
Background Information
Credits
For a paper copy of this guide, go here.
Description
This activity will complement the astrobiology exhibit in the Portal space as well as the two astrobiology sphere demonstration, Pale Blue Dot and Ancient Earth. The exhibit will focus on finding planets outside of our solar system, much like the Strange Planets Discovery Cart and the Pale Blue Dot. Meanwhile, this activity is about conditions necessary for life, from the Earth's surface to the atmosphere. Like Ancient Earth, this activity uses Earth as a model and explores Earth's history to discover what we are looking for when we search other planets for life. In addition, this activity explores the evolution of life on Earth to explore the time and natural processes necessary for intelligent life to evolve.
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Concepts
- The evolution of life on Earth drastically changed the composition of Earth's atmosphere, which made life as we know it possible.
- The evolution of intelligent life as we know it involved a very long period of time and very specific conditions.
Learning Objectives
- By identifying important events in Earth's history and putting them in order, guests will learn how different events influenced each other, and what was necessary for various life forms to evolve.
- Guests will place objects on a timeline, which will enable them to visualize how long the process of evolution takes.
How To Demonstrate
- Attract visitors to your activity by asking them questions like, "Do you think there's life on other planets?" or, "Want to help me make a timeline?"
- Give the visitors a prop, explaining that it represents an event in Earth's history. Help them guess the event it represents. Give them some other props (you don't have to use them all) and help the guests guess which event the objects represent.
- Ask the guests to put the objects in order according to when they happened in Earth's history. Explain that Earth's history is important when talking about the potential for life on other planets, and discuss why. Ask them whether they think the events they're putting in order have happened on other planets.
- Next take out the rope and stanchions, explaining that the rope is 4.6 billion year's long--the age of the Earth. The hooks represent different events. Encourage the guests to hang the "events" when they think they occurred. To check their answers, guests can use the cards with the actual years on them.
- Ask the guests what they notice about the timeline and have them discuss how the events are spaced. Ask which of the events were important for human beings to evolve. Based on this information, ask what they think scientists look for in a planet that might have intelligent life.
Questions To Ask
- Have you heard the term "astrobiology"?
- What does the history of Earth have to do with astrobiology?
- What do you think scientists look for when they look for life on other planets?
- Why is Earth a good model for understanding things in outer space?
- How do you think life has changed the Earth?
- How do you think living a million years ago would be different? How about 100 million? A billion?
- What conditions are necessary for life?
- Why are plants important to evolution? What about the ocean? What about the Sun?
Background Information
Click to jump to any of these topics:
Astrobiology
Geologic Timeline
Earth
Ocean
Solid Land
Life
Cyanobacteria
Algae
Animals
Cambrian Explosion
Fish
Plants
Insects
Forests
Amphibians
Reptiles
Dinosaurs
Mammals
Birds
Flowers!
Humans
Astrobiology__________________________
From the website of the University of Washington Astrobiology Program (UWAB):
Astrobiology is the study of life in the universe. The search for life beyond the Earth requires an understanding of life, and the nature of the environments that support it, as well as planetary, planetary system and stellar processes. To provide this understanding, astrobiology combines the knowledge and techniques from many fields, including astronomy, biology, chemistry, geology, atmospheric science, oceanography and aeronautical engineering. Astrobiologists can work alone on particular scientific questions, but often astrobiologists from different scientific disciplines work together to examine complex questions that no one field can answer alone. These questions cover topics such as:Regarding why studying Earth's history is necessary to astrobiology, the UWAB website had this to say:
- How does life originate?
- How does life evolve?
- What kind of environment is necessary for life to survive?
- What are the environmental limits or “extremes” under which life can survive?
- What might life look like on another world?
- Is there or has there been life elsewhere in our solar system?
- How can we observe and identify a habitable – or even inhabited – world?
- What is humanity’s future on Earth and beyond?
Earth will always be the most accessible habitable planet for study. Consequently, studying the origin and earliest evolution of life, along with the long-term evolution of the Earth’s environments, helps us understand why the Earth became habitable and why terrestrial life has persisted for billions of years. The earliest environments on Earth are also very unlike our modern-day environment, and serve as alternate examples of “habitable planets.” Earth's climate has been influenced by the Sun, which has gradually brightened by 25-30% in the last 4 billion years, and by the presence of greenhouse gases, many of which are produced by microbial life.Regarding what is currently being studied in astrobiology, the UWAB website states:
While astrobiology is a relatively young field, it has a secure and promising future. Astrobiology research has a significant impact on how agencies such as the National Aeronautics and Space Administration (NASA) and the European Space Agency plan for current and future space missions. For example, many recent missions have focused on exploring worlds in our own solar system for signs of past, present or the precursors of life, including Mars (Phoenix , Pathfinder , Global Surveyor, and others) and Titan (Cassini-Huygens ). At the same time, significant advances and investments in telescope technology (Kepler, James Webb Space Telescope) have allowed researchers to begin planning and searching for habitable planets outside our solar system.The UWAB website is a good place to start for more information: here.
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Geologic Timeline__________________________
Geologic time is the immense span of time that has elapsed since planet Earth first formed—almost 4.5 billion years ago—to the recent times. The geologic time scale is a way of looking at this vast history in an orderly fashion. Units of time on the geologic time scale (eons, eras, periods, epochs) are not defined by a consistent length of time (for instance, an era is not always 100 million years). Rather, they are defined by events in earth’s history.
Time is first divided into the Phanerozoic Eon, the eon in which we live, as well as the Precambrian supereon, which comprises three eons. During the Precambrian time Earth formed and single-celled organisms lived. The event that marks the beginning of the Phanerozoic Eon is the Cambrian Explosion. Eons are split into eras; the Phanerozoic eon is split into three eras: the Paleozoic, Mesozoic, and Cenozoic. Mesozoic means “middle”. Eras are split into periods, and periods are split into ages.
The University of California Museum of Paleontology has a web page about this, complete with a timeline graphic here. Keep in mind that many graphics, such as this one, do not properly show the scale of the Phanerozoic time versus Precambrian. Almost three quarters of history are Precambrian.
Scientists use the geologic timescale to date Earth's strata, which they use to date fossils they find. (Scientists have a hard time getting dates sometimes. I'm hilarious.) The geologic timescale is also a quick way to reference time frames, instead of saying "billions of years ago" all the time. Another way they save time (I'm on a roll here) is to use the following notations:
Ga - gigaannum, or billions of years ago
Ma - miloannum, or millions of years ago
Ka - kiloannum, or thousands of years ago
They may also use "Gyr" to mean billion years or "Gya" to mean billions of years ago; similar formations are used for millions and thousands. Sometimes billions of years are also abbreviated to Byr or Bya.
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Earth __________________________
The solar system formed 4.56 Ga when a cloud of gas and dust called the solar nebula began to contract and spin. Gas and dust particles orbiting the early Sun collided and stuck together (a process called accretion) to form planets, asteroids, meteorites, and other solar system objects.
In the 1950s, Dr. Claire Patterson measured the decay of uranium into lead, which occurs at a constant rate over billions of years, in a meteorite that formed at the same time as Earth did. He determined that the meteorite, and by extension Earth, is 4.55 Ga. Later work by scientists studying other meteorites and the Moon has refined this date to 4.56 Ga.
The BBC has a great overview of this: The Earth Forms. For more information, talk to Laura Grace!
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Ocean __________________________
Scientists have not yet agreed on how and when the oceans formed. One leading hypothesis is that the oceans formed from degassing of water vapor from water-containing minerals inside the Earth. Another possibility is that asteroids and other small planetary objects delivered water to the early Earth via impacts. Both processes--degassing from Earth’s interior and delivery of water from asteroids--may have played a role in creating Earth’s oceans. The salt in Earth’s oceans was leached from salt-containing rocks.
Scientists estimate that it took millions of years for water to accumulate to form Earth’s oceans, meaning that the first oceans may have existed by 4.4 Ga. Earth may have had oceans before the surface had cooled below the boiling temperature of water thanks to high pressure from a thick atmosphere of greenhouse gases.
This article on LiveScienceprovides a great overview: Where Did Earth's Water Come From? For more information, talk to Laura Grace!
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Solid Land __________________________
Earth may have had a solid surface within a few tens of millions of years after its formation, but likely none of that initial surface has survived to the present day. Frequent impacts, including the Moon-forming impact, continually re-worked the Earth‘s surface over the next few hundred million years. Any solid rock that did remain from the first few hundred million years has probably been buried and reformed by plate tectonic activity.
The date of the oldest rocks on Earth is highly contentious. A section of gneiss (pronounced “nice”), a kind of metamorphic rock, from the Northwest Territories in Canada has been dated to 4.03 Ga. Some scientists assert that rocks from the Nuvvuagittuq formation on the eastern shore of Hudson Bay in northern Quebec are up to 4.28 Ga, although other scientists believe these rocks may be only 3.8 Ga. Rocks are made of minerals, and the oldest individual mineral has been dated as 4.37 Ga, which suggests that solid land was present by that time.
This interesting news article provided by NSF (National Science Foundation) is an example of scientists getting excited about rocks: Oldest Known Rock On Earth Discovered. For more information, talk to Laura Grace! Or Zeta--she likes rocks.
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Life__________________________
The first lifeforms were likely single-celled microorganisms, but scientists do not know what kind of microorganism or when they evolved. The origin of life on Earth probably occurred sometime between 3.5 to 4.1 Ga. It is possible that life formed even earlier, but was wiped out by one of the frequent impacts on the early Earth. We know that life has existed for at least 3.5 billion years because multiple microfossils, which are fossils of microorganisms, and several stromatolites, which are layered sediments that may have been formed by microbial mats, have been dated to 3.5 Ga.
Other scientists consider isotopically light carbon, which today forms via biological activity, as a sign of life. Mojzsis et al. (1996) reported light carbon isotopes in 3.8 Ga rocks in Greenland, which they interpreted as evidence for life. More recently, Bell et al. (2015) reported isotopically light carbon in a single mineral crystal from 4.1 Ga. Whether these light carbon isotopes are indicative of biological processes or could form by some other mechanism is still debated.
Laura Grace brought in a great textbook called Planets and Life: The Emerging Science of Astrobiology that is currently sitting on the back table in the SIP Library. All you need in order to present the Timeline of Earth activity are things you should have heard in 9-Times--you do not need all the specifics. However, if you are curious and would like to learn more, please check out the book! Please be aware this belongs to Laura Grace and she is loaning it to us because she is a magnificent land mermaid; treat her property with care and respect. And bring her flowers; I bet she'd like them.
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Cyanobacteria__________________________
The origin of oxygenic photosynthesis is one of the most important biological process in the history of life on Earth because it changed the chemistry of the oceans and the atmosphere.1 Some studies suggest that organisms capable of oxygenic photosynthesis evolved almost 3.5 billion years ago, not so long after the time life is thought to have first appeared.2 These early organisms were likely bacteria, much like cyanobacteria.
The date at which cyanobacteria as we know them first appeared is still debated; however, many think they appeared on the scene 2.5 to 2.7 billion years ago. For the next few 100 million years, they photosynthesized, converting Earth's carbon dioxide atmosphere into oxygen. Much of this oxygen was taken in by organic matter and iron, but by 2.3 billion years ago, these sinks were already full of oxygen, so more oxygen went into the atmosphere, changing its composition. This is known as the Great Oxigenation Event, or GOE (sometimes also known as the Oxygen Crisis, Oxygen Catastrophe, or Great Oxidation). The GOE made most life as we know it possible.
This article in Scientific American provides a brief yet interesting overview: The Origin of Oxygen in Earth's Atmosphere. Ask Carolina for more information!
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Algae__________________________
Approximately 1.7 billion years ago, unicellular or singled cell eukaryotes started to form colonies and ultimately each member of the colony adopted specific tasks, which lead to the transition from a colony of singled celled organisms to multicellular organisms. Some of the first of these multicellular organisms were algae. The first algae were red and brown and photosynthesized, much like cyanobacteria, but not as well as green algae, which appeared around 400 million years later.
This article in Scientific American helps to shed some light (ho ho ho!) on the history of photosynthesis on Earth: Timeline of Photosynthesis on Earth.
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Animals__________________________
Something frustrating about finding out what was the first animal on earth is that bony structures (most easily fossilized) didn’t show up for a very long time; it’s much more difficult to find evidence of soft-bodied organisms in the form of fossils. Though there’s been much contention about whether Earth’s first animal was the comb jelly or the sea sponge, a recent study found genetic evidence of sea sponges in 640 million-year-old rock. This pre-dates the Cambrian Explosion by about 100 million years and brings up many questions about what the environment was like and why there is such a huge gap in the fossil record. Molecular fossil research can potentially help answer these questions in the future.
This article from Massachusetts Institute of Technology (MIT) provides an overview of recent discoveries about this topic: Title for 'Earth's First Animal' Likely Goes to a Simple Sea Creature. For more information, talk to Julia!
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Cambrian Explosion__________________________
The Cambrian Explosion revealed a huge diversity of marine animal life. Trace fossils from the period preceding the Cambrian period mostly included burrows from worms. These, along with some shell fragments, showed up in the beginning of the Cambrian period as well. It wasn’t until about 520 million years ago that whole-body fossils formed along with almost all other animal groups, indicating that during the 20 million-year span there was an explosion of evolution. Some hypotheses for why this happened are as follows:
-animals took a long time to evolve the necessary genetics to be mobile
-most animals preceding the Cambrian period were soft-bodied and therefore did not fossilize well
-it took until the Cambrian period for animals to be able to burrow, which ventilated the sediment and assisted in the productivity in that environment, allowing for more complex life to radiate into different niches.
-the Cambrian period reveals the first real predators, which would add a significant evolutionary pressure
-one suggested trigger for the Cambrian explosion is a gamma ray burst event which allowed some photons to reach the sea level and essentially induce as mass-mutation event hence the sudden diversity of life
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Fish __________________________
Some contend that the Pikaia, an extinct worm-like marine organism, is the ancestor of all modern fishes--and consequently, all vertebrates. Pikaia is defined as a fish because it seems to have had a spinal cord protected by a hard structure, which makes it a member of the phylum chordata. Most organisms in chordata are vertebrates, meaning they have bones and vertebrae that protect the spinal cord, but some, like this early fish and sharks, don't have bones, just the spinal cord protected by cartilage, which also comprises the rest of their internal structure.
Early on, some organisms evolved from this fish to be the ancestors of modern sharks and rays. Later, other descendants of this fish evolved into ray-finned fish, which have bones and a spine, but have no bony limbs. Modern fish like bass and salmon descended from these early ray-finned fish. Still later, other descendants of Pikaia (or a similar early fish) became the lobe-finned fish. The lobe-finned fish, which contained bony structures in their fins, are the ancestors of the first amphibians, and therefore are the closest fish ancestor of humans.
This article from the University of Cambridge talks about some research on Pikaia: Human's Oldest Ancestor Found. Be aware that this article was published in 2012, and new research might have emerged since then.
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Plants __________________________
Plants were among the first organisms to live solely on land. The first plants were non-vascular, meaning they did not have internal structures (xylem and phloem) that allow for the transport of nutrients. Non-vascular plants, also known as bryophytes, are therefore simpler in structure. Bryophytes include plants such as mosses, hornworts and liverworts. Bryophytes don’t produce flowers or seeds; instead, they reproduce through spores.
Spore-like structures present in the middle Cambrian shales in Tennessee and the Grand Canyon indicate the first presence of land plants as simple bryophytes.3 Liverworts were first found in rocks between 473 million and 471 million years ago, during the Ordovician Period. Moss fossils are first found in the Permian Period (299 million to 251 million years ago). The first plant known to have a stem with vascular tissue belongs to the Cooksonia genus (an extinct group of primitive land plants) and it is considered to be the transition between non-vascular to vascular plants.
If you would like to know more about this topic, Encylcopedia Britannica has a pretty good rundown here: Evolution and Paleobotany. Or ask Carolina!
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Insects__________________________
Insects were the first animals to live solely on land. For a long time, scientists thought--based on fossil records--that insects emerged 400 - 412 million years ago. However, only a few years ago, a team of scientists (and a bunch of interested lay people, who contributed specimens) were able to genetically sequence lots of different species of insects. Because there are so many different types of insects, this could only be accomplished relatively recently with the help of very powerful computers. When scientists compared all this sequencing to the fossil record, they concluded that insects had to have evolved at least 60 million years earlier than they had originally supposed. They now date the emergence of insects around the same time as the emergence of plants. Flying insects--the first organisms to fly of their own power--did not emerge until 406 million years ago.
This data was interesting because insects today are very important to the survival of plants and vice versa. Scientists have known for a long time that these two groups have influenced each other's evolutionary trajectory--plants evolving to be attractive to pollinators, for instance, and insects evolving to be good pollinators. The fact that these two groups appeared on land at around the same point in Earth's history suggests that the existence of one contributed to the success of the other.
This is an article from the American Association for the Advancement of Science (AAAS) (...which is based on an article from Science magazine) is about the genomic sequencing of insects, which led to these discoveries: Science: Insects Evolved With Earth's First Land Plants.
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Forests__________________________
Most terrestrial plants in the early Devonian (420-390 million years ago) were small. By the mid-Devonian (around 390 million years ago) terrestrial plants experienced its greatest diversification, evolving from small vascular plants to dense vegetation with trees over 35 meters tall.3 Trees or tree-like plants from the genus Wattieza and Archaeopteris are the first trees known in the fossil record. The tree-like plants from the mid-Devonian proliferated through the Carboniferous (360-300 million years ago). The Carboniferous is named for these early forests.
Vegetation was so dense at this time that when it died, it didn't always have time to decompose before being covered by more dead vegetation. As a result, much of this rotting vegetation formed peat, creating dense, swampy areas. Over time, as this peat was buried more deeply and compressed by the Earth, fossil fuels formed. Much of the fossil fuels we burn today was made from these ancient forests.
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Amphibians__________________________
Amphibians as we know them today didn't exist 360 million years ago. Rather, the lobe-finned fishes of the time evolved into tetrapods, vertabrate amphibian-like creatures whose closest living relatives are today's lungfish. "Tetra" means four and "pod" means foot, so tetrapod means four-footed animal. Today, the term tetrapod includes animals such as snakes, whales, and humans. Even though they don't have four feet, they evolved from early tetrapods. Tetrapods were the first vertebrates to walk on land (insects were the first animals), and eventually diversified into reptiles, which diversified further into birds and mammals.
Some scientists theorize that competition with reptiles killed off a lot of early amphibians, which eventually evolved into the frogs, salamanders, and axolotls we know today. As shallow-water predators, it became increasingly advantageous to develop weight-bearing legs instead of fins. The nostrils and eyes being on top of the head made it easier to spot out-of-water prey. Other characteristics of early amphibians include rib cages (to eventually aid lungs in respiration), interior gill-like structures.
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Reptiles__________________________
Tetrapods evolved into two distinct groups: amphibians and amniotes. Amniotes are a group of vertebrates that include reptiles, birds, and mammals, and are characterized by the membranes that surround the embryo as it develops. These membranes gave eggs the strength and protection to be deposited on land. Amphibian eggs are more delicate and are always laid in water.
Technically, calling these early amniotes reptiles is incorrect. "Reptiles," like the terms "amphibian," "mammal," and "bird" are classifications that describe current groups. Early reptiles were the first vertebrate animals to survive only on land (insects had already been around for a while). According to current fossil record, the first reptile was Hylonomus lyelli, a small lizard-like animal that ate mainly insects.
Eventually, amniotes diversified into the synapsids (which later became mammals) and sauropids, which later further diversified into dinosaurs and reptiles we know today.
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Dinosaurs __________________________
Dinosaurs emerged in the Triassic period, around 240 million years ago, right after the worst mass extinction in Earth’s history (at the end of the Permian). In this early dinosaur time the dinosaurs lived alongside many other species of animals. They didn’t really rise above to become the dominant animal group until they reached the point in their evolution characterized by long, upright limbs and 20 million years later became what are now the most commonly recognized dinosaurs.
Some of the earliest evidence of Triassic dinosaurs (dinosauromorphs) comes from the Chinle Formation in the southwest of the US, which also shows the diversity of fauna during this period in dinosaur evolution.
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Mammals __________________________
Mammals evolved from synapsids, which were reptile-like animals that evolved before the Mesozoic Era. Synapsids included large animals like Dimetrodon, which some people mistake for a dinosaur. Dimetrodon looked like a crocodile with a large fin on its back--it is not necessarily the direct ancestor of mammals, but is a good example because many people recognize it.
One of the earliest mammals was a small, shrew-like creature called a Morganucodontid. Morganucodontids belong to a group known as Prototheria, which are mammals that lay eggs. Very few mammals lay eggs today; Prototheria later diversified into marsupials and placentals--mammals who give birth as humans do.
This article from National Geographic is about the evolution of mammals: The Rise of Mammals.
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Birds__________________________
Most scientists generally agree that birds evolved from dinosaurs. The debate is now about which dinosaur specifically evolved into the first bird. Many scientists agree that therapods, a group of carnivorous raptors that walked on two legs, are the ancestors of birds. Therapods include Deinonychus, the Velociraptor, and Tyrannosaurus Rex.
Archeopteryx is a very famous fossil discovered in the nineteenth century that demonstrates a transition between birds and dinosaurs. Over time, scientists have debated about whether to classify it as a dinosaur or bird. It is currently classified as a dinosaur and is not considered to be the direct ancestor of birds, though it was possibly related to the direct ancestor of birds. Archeopteryx is around 150 million years old.
This article from National Geographic is about the discovery of a new "bird-like" fossil, and the difficulty scientists have had in identifying the first "true" bird: New Candidate for World's First Bird. (back to topic list)
Flowers! __________________________
Flowering plants are known as angiosperms. The main characteristics of angiosperms are the production of fruits, which contain seeds that are developed inside the ovary of a flower. The oldest fossil evidence for angiosperms is from the Early Cretaceous (120 million years ago). 3, 4. The expansion of angiosperms occurred rapidly and by the Late Cretaceous flowering plants were more diverse than any other land plant. The rapid expansion and diversification is attributed to the increasing global temperatures in the early Cretaceous, when the break-up of Pangea initiated and volcanoes released CO2 into the atmosphere increasing temperatures by almost 8 °C.3
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Humans__________________________
The earliest fossils of Homo sapiens were found in Ethiopia. A couple of shared traits in great apes include: larger prefrontal cortex portion of the brain leading to social groupings, dominance hierarchies within social groups. Though there is some discord on the extent of the relationship between Neanderthals and humans when both species lived, there is evidence to suggest the last common ancestor lived in the middle Pleistocene.
Early Homo sapiens are characterized by a comparatively large brain, bipedalism, and a prominent chin. The fossil record and archaeology of sites of Homo sapiens is used to infer behavior about the species. Complex tools indicate the ability to hunt for better food, and drawings or jewelry in burial sites tell about the ability to understand and use symbolism. Neanderthals were also bipedal but with distinctions such as a wider pelvis, much bigger bones, and large noses and eyes. Neanderthals lived from 300,000 to about 27,000 years ago.
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Credits
Activity creation: Joy DeLyria and Lauren Slettedahl
Prop creation: Lauren Slettedahl
Cards and activity write-up: Laura Grace Beckerman, Joy DeLyria, Julia Lippert, and Carolina Mor
Works Cited:
1. Konhauser, K. (2009). Biogeochemistry: deepening the early oxygen debate. Nature Geoscience, 2(4), 241-242.
2. Hoashi, M., Bevacqua, D. C., Otake, T., Watanabe, Y., Hickman, A. H., Utsunomiya, S., & Ohmoto, H. (2009). Primary haematite formation in an oxygenated sea 3.46 billion years ago. Nature Geoscience, 2(4), 301-306.
3. Sullivan III, W. T., & Baross, J. (Eds.). (2007). Planets and life: the emerging science of astrobiology. Cambridge University Press.
4. Schneider, H., Schuettpelz, E., Pryer, K. M., Cranfill, R., Magallón, S., & Lupia, R. (2004). Ferns diversified in the shadow of angiosperms. Nature, 428(6982), 553-557.
Further References:
The Acasta gneiss: Earth's oldest surface rock. Science Buzz. 2017. Web. Mar. 2017.
Bell, E. A., Boehnke, P., Harrison, T. M., Mao, W. L. Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon. Proceedings of the National Academy of Science. 112:47, 14518-14521 (2015). DOI: 10.1073/pnas.1517557112.
Brusatte, Stephen L. Evolution: When Dinosaurs Bested Their Early Rivals. Current Biology, Volume 26, Issue 22, 21 November 2016, Pages 3090-3095
Buick, R. The earliest records of life on Earth in Planets and Life: The Emerging Science of Astrobiology. (Sullivan, W. T. and J. A. Baross, ed). Cambridge University Press, 2007.
Burgess Shale. Smithsonian National Museum of Natural History. 2017. Web. Mar. 2017.
California Academy of Sciences. Landmark study on the evolution of insects. ScienceDaily. ScienceDaily, 6 November 2014. Web. Mar. 2017.
Caroll, Robert L. Revealing the patterns of macroevolution. Nature Vol. 381. 2 May 1996. Web. Mar. 2017.
Chen, Pisin and R. Ruffini. "Did Gamma Ray Burst Induce Cambrian Explosion?." Astronomy Reports, vol. 59, no. 6, June 2015, pp. 469-473. EBSCOhost, doi:10.1134/S1063772915060098.
Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. The Origin and Evolution of Cells. Web. Mar. 2017.
Dorminey, Bruce. Earth Oceans Were Homegrown." Science. AAAS. 29 Nov. 2010. Web. Mar. 2017.
El-Showk, Sedeer. Accumulating Glitches: Exploring the grandeur of evolution. Scitable. 8 Jul. 2013. Web. Mar. 2017.
Fish. Marine Education Society of Australia. Web. Mar. 2017.
Fossil insects – 400 million years of evolution. Museums Victoria. Web. Mar. 2017.
Fox, Douglas and Michael Le Page. Dawn of the animals: Solving Darwin’s dilemma. New Scientist. 8 Jul. 2009. Web. Mar. 2017.
GEOL 104 Dinosaurs: A Natural History. University of Maryland. 14 Aug. 2016. Web. Mar. 2017.
Gale, Joseph. Astrobiology of Earth: The Emergence, Evolution and Future of Life on a Planet in Turmoil. OUP Oxford, Apr 16, 2009. Web. Mar. 2017.
Holmes, Bob. Sparks of Life. New Scientist, vol. 225, no. 3010, 28 Feb. 2015, pp. 38-41. EBSCOhost.
Hylonomus: The Earliest Reptile. Natural History Notebooks. Canadian Museum of Nature. 3 Mar. 2017. Web. Mar. 2017.
Kasting, J. and Catling, D. Evolution of a Habitable Planet. Annual Review of Astronomy and Astrophysics 41, 429-463. 2003.
Lahr, Marta Mirazón. The shaping of human diversity: filters, boundaries and transitions. Phil. Trans. R. Soc. B 2016 371 20150241; DOI: 10.1098/rstb.2015.0241. Published 13 June 2016. Web. Mar. 2017.
McBride, N. and Gilmour, I.ed. An Introduction to the Solar System. Cambridge University Press, 2003.
Michel Laurin, Robert R. Reisz. A reevaluation of early amniote phylogeny. Zool J Linn Soc 1995; 113 (2): 165-223. doi: 10.1111/j.1096-3642.1995.tb00932.x.
Mojzsis, S. J., G. Arrhenius, K. D. McKeegan, T. M. Harrison, A. P. Nutman, and C. R. L. Friend. Evidence for life on Earth before 3,800 million years ago. Nature. 384, 55-59 (1996). DOI:10.1038/384055a0.
Morbidelli, A., J. Chambers, J. I. Lunine, J. M. Petit, F. Robert, G. B. Valsecchi, and K. E. Cyr. Source regions and timescales for the delivery of water to the Earth. Meteoritics &Planetary Science 35:6, 1309-1320. 2000.
Nix, Steve. Evolution of Forests and Trees: Understanding How the Earth's First Forests Developed. ThoughtCo. 18 Feb. 2016. Web. Mar. 2017.
Noffke, N., Christian, D. Wacey, D. and R.M. Hazen. Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia. Astrobiology. 13:12, 1103-1124 (2013). DOI: 10.1089/ast.2013.1030.
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