Questions about the Early Earth

Participants at the early earth workshop were asked to submit a question about the early earth, along with and answer that includes the current state of what we know.

Some of the questions and answers have been expanded into a longer form and can be found on the Key Questions about the Early Earth page.

Atmosphere, Hydrosphere, and Climate | Life | Solid Earth | Teaching

All the key questions and answers (Microsoft Word 107kB Apr3 07), handy for printing.

Atmosphere, Hydrosphere, and Climate

When did oceans form on Earth? What evidence is preserved in the rock record?

What was the nature of the pre-biotic terrestrial atmosphere?

What is the evidence for and against a widespread glaciation event such as the "Snowball Earth"? Is the alternative "Slushball Earth" a viable alternative? Is the difference between the two really matter?

As a sedimentologist, I am interested in how we are using BIF (banded iron formation) deposits to understand the evolution of the atmosphere?

How can data on the CO2 concentration and isotopic signature of the early atmosphere provide us with more information on processes on and in the early earth?

Why is the oxygenation of Earth's atmosphere irreversible?

What is the geologic evidence for anoxic or very low free oxygen levels during the early history of the Earth and the timing of the transition to a relatively stable free oxygen atmosphere?

What mechanisms initiated glaciation in the late Archean and early Proterozoic, and what allowed Earth's climate to recover from these glacial periods?

What do we know about the origin of water and oceans on earth?

What do we know about the origin of the atmosphere/hydrosphere system?

How can we extrapolate backwards to understand the conditions of the Hadaean Earth?

How deep and what was the temperature of the ocean in the Archean time?

The fascinating thing about the Precambrian is its uniqueness with respect to today's environments on Earth. There are so many possible topics. My interest in teaching aspects of the Early Earth is mostly in regard to undergraduate general education students so I am looking for sources and techniques that would allow for some exploration of these aspects through exercises or very small projects worked by individuals or groups. But! The directions demand one question so: The oxygenation of the Earth's atmosphere.


How have changes in two important environmental variables, temperature and salinity, influenced the evolution of microbes in the Precambrian ocean?

What is the current status in our understanding of RNA world, a possible precursor to DNA based life forms? Is this hypothetical world still a viable way for us to understand the origin of life?

What do we know about the origin of life on Earth?

Where do we currently stand as to where and when life evolved on early earth?

Is the early evolution of life on Earth the key to resolving the Faint Young Sun paradox?

What is the current best model for the evolution of organic life from non-living organic molecules? What environmental conditions were most likely present at that time how did they promote the formation of living organisms and what is the evidence to support this?

What factors (physical/chemical/biological) triggered the evolution of eukaryotes after a lengthy dominance of early Earth by prokaryotes?

How is the discovery of hydrothermal vent communities and chemosynthetic archaea changing our views of the early evolution of life on earth?

Banded Iron Formation (BIF) and stromatolites: evidence for shallow water environment and organic theory of BIF? An oversimplification?

Solid Earth

How well do carbonaceous chondrites approximate the bulk composition of the Earth?

When and how did continental crust form? What evidence supports models that call for a) early extraction of all the crust from the mantle, b) long-term growth, or c) episodic periods of crustal growth? Did most of the crust form by the end of the Late Archean? Has there been a secular change in the composition of the Archean crust compared with the Phanerozoic crust?

What was the structure of the crust like when the first major continent formation occurred? What changed circa 3.5 Ga to allow preservation of crust? Considering that the oldest types of rocks we see today are high-grade gneisses does that mean that there was a thick felsic crust? How could that form in the early scenario of reworked crust?

When did the earth's crust form and what was its initial composition?

What is the significance of the Jack Hills zircons?

When did plate tectonics begin on the earth?

From the perspective of the geosphere, what changed during the transition from Archean to Proterozoic time? Did the Earth cool to some critical threshold? Was it a gradual and continuous process, or were there events or processes that perturbed mantle processes (such as the introduction of recycled water back into the mantle)? What evidence do geologists, geophysicists, and geochemists have for changing mantle processes across the Archean-Proterozoic transition?

How old is the Earth?

If the Earth's mantle was hotter during Archean times (as suggested by the abundance of komatiites in greenstone belts), how would this affect global tectonic regimes during the Archean?

When did Phanerozoic-style plate tectonics (lateral motion of rigid lithospheric plates) begin?


It is part of the standard procedure of teaching general geology to students to explain the past in terms of the present processes i.e. "The Present is the Key to the Past". This uniformitarian viewpoint has served us well for many years. However there are many processes in the Early Earth that are non-uniformitarian. How do we address that viewpoint when talking about the Early Earth to students and colleagues?

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