earth science

Tonian

Tonian is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Tonian rather than just read about it. In short: The Tonian (from Ancient Greek: τόνος, romanized: tónos, meaning "stretch") is the first geologic period of the Neoproterozoic Era. It lasted from 1000 to 720 Mya (million years ago).

Key takeaways

Tonian belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tonian to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tonian from memory before moving on to harder problems.

Reference excerpt

The Tonian (from Ancient Greek: τόνος, romanized: tónos, meaning "stretch") is the first geologic period of the Neoproterozoic Era. It lasted from 1000 to 720 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based on radiometric chronometry. The Tonian is preceded by the Stenian Period of the Mesoproterozoic Era and followed by the Cryogenian.

History The Tonian was defined in 1990 by the New Precambrian time scale as being from 1000 to 850 Mya. The name Tonian comes from Ancient Greek: τόνος, romanized: tónos, which means "stretch", referring to the rifting that broke up Rodinia during this period. The upper definition was then redefined to 720 Mya in 2014 after discoveries that the original 850 Mya for the lower Cryogenian and the first glaciations at 717 Mya did not match. This is temporary until the basal Cryogenian GSSP is chosen.

Geology Both the Supercontinent Rodinia and the Mirovian superocean remained stable throughout the early Tonian from 1000 to at least 900 Mya. The appearance of sedimentary rocks in multiple places in 850 to 800 Mya has been postulated as an initial breakup of Rodinia. However, there has been little evidence for the breakup of Rodinia during the mid-Tonian, with most agreeing that Rodinia began breaking up at the end of the Tonian, around 750 Mya. The first half of the Tonian has mildly fluctuating carbon isotope values, being transitional from the lower Mesoproterozoic levels to the higher Tonian levels. The later half of the Tonian has high carbon isotope values, with deep excursions happening at least once after 740 Mya, immediately before the Sturtian glaciation in the Cryogenian.

Biology

The first putative metazoan (animal) fossils are dated to the middle to late Tonian (c. 890 to 800 Ma). Fossils of Otavia antiqua, which has been described as a primitive sponge by its discoverers and numerous other scholars, date back to about 800 Ma. Even earlier sponge-like fossils have been reported in reefs dating back to 890 Ma, but their identity is highly debated. This dating is consistent with molecular data recovered through genetic studies on modern metazoan species; more recent studies have concluded that the base of the animal phylogenetic tree is in the Tonian. Tonian rocks preserve some of the earliest known fossils of macroalgae, such as the benthic macroalgae from the Longfengshan biota of the Luotuoling Formation or the green algae from the Dolores Creek Formation. Arctacellularia tetragonala, an alga found in this period, has chlorophyll derivatives preserved in it. Sinosabellidites huainanensis, another alga from the Huainan biota that was initially confused for an animal, was found in this period. The first large evolutionary radiation of acritarchs occurred during the Tonian. Late Tonian sediments abound in vase-shaped microfossils that represent the earliest known testate amoebozoans. Stromatolites begin to swiftly decrease during this period. Fungi are visibly preserved in this period in 810 to 715 million year old shale in the Mbuji-Mayi Supergroup with mycelia-like filaments.

See also Boring Billion – Earth history, 1.8 to 0.8 billion years ago Neoproterozoic oxygenation event Huainan biota

References

Further reading "Tonian Period". GeoWhen Database. Archived from the original on May 12, 2006. Retrieved January 5, 2006. Ogg, James G. (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia. 37 (2): 183–199. Bibcode:2004Letha..37..183O. doi:10.1080/00241160410006492.

Illustrations

Worked examples

Example 1 — a first encounter with Tonian

Start with the simplest possible case. Write down what Tonian claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Tonian before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Tonian ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Tonian

In research: Tonian appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Tonian in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Tonian is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geological periods, Neoproterozoic, Proterozoic geochronology, so understanding it makes those chapters shorter.
In everyday life: Look for Tonian outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Tonian in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tonian means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Tonian out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tonian in simple terms?

The Tonian (from Ancient Greek: τόνος, romanized: tónos, meaning "stretch") is the first geologic period of the Neoproterozoic Era. It lasted from 1000 to 720 Mya (million years ago).

Why does Tonian matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Tonian?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Tonian.