17.4: Earth's oldest fossils?
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The Nuvvuagittuq Greenstone Belt continues to give. In 2017 a team of researchers presented their findings on what they believe to be traces of life found in the banded iron formation of the NGB [13]. Their microscopic investigation of the BIF revealed small tubes made of the iron mineral hematite. These tubes match the shape and size of those made by bacteria in modern hydrothermal vent environments. The bacteria use the iron for their metabolism. The researchers also discovered the mineral graphite in the BIF which is composed entirely of carbon. The graphite likely formed by metamorphism of organic material as it contains reduced levels of the heavy carbon isotope, carbon-13 (\(\ce{^{13}C}\)). Lifeforms are preferential in selection of the lighter isotope of carbon, carbon-12 (\(\ce{^{12}C}\)).
If this discovery holds true, this will be the oldest evidence of fossil life yet discovered. The NGB banded iron formation exists within the NGB and can be interpreted as having been deposited on the ancient sea floor represented by the greenstone. This NGB has been unquestionably dated by cross-cutting igneous intrusions at 3.77 Ga. This would pre-date any fossil evidence previously discovered by several hundred million years (see In the Beginning). If O’Neil’s age for the NGB holds up, then the fossils may perhaps be as old as 4.31 Ga.
Did I Get It? - Acasta Gneiss and Nuvvuagittuq Greenstone Belt Quiz
Is the Acasta Gneiss Complex Hadean in age?
a. No, none of the samples from Acasta Gneiss Complex date to the Hadean, they are 3.92 Ga which is Eoarchean in age.
b. Yes, some of the samples of the Acasta Gneiss Complex have been dated to 4.04 Ga which is in the Hadean Eon of geologic time.
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b. Yes, some of the samples of the Acasta Gneiss Complex have been dated to 4.04 Ga which is in the Hadean Eon of geologic time.
How do we know that the Acasta Gneiss Complex is Hadean in age?
a. The Acasta Gneiss rocks have been isotopically dated using zircon crystals.
b. The Acasta Gneiss is composed of TTG rock which is from Earth's first crust.
c. The Acasta Gneiss contains fragments of the Earth's first komadiite crust.
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a. The Acasta Gneiss rocks have been isotopically dated using zircon crystals.
How do we know that the greenstone from the Nuvvuagittuq Greenstone Belt is rock from the ocean crust?
a. The greenstone contains zircon crystals which are common in rock of the ocean crust.
b. The greenstone contains pillow lava structures which indicate the eruption of lava underwater.
c. The greenstone is composed of TTG rock which is the most common rock of the ocean crust.
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b. The greenstone contains pillow lava structures which indicate the eruption of lava underwater.
Why is the age of the Nuvvuagittuq Greenstone Belt (NGB) questioned?
a. The location of the NGB is so remote that other scientists have not been able to investigate the rock and validate the claim.
b. Zircon has not been found in the greenstone rock of the NGB therefore U/Pb isotopic dating cannot be used which is the "gold standard" in dating very old rock.
c. The team of NGB geologists have not collected enough samples with zircon therefore the isotopic dates provided are not reliable.
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b. Zircon has not been found in the greenstone rock of the NGB therefore U/Pb isotopic dating cannot be used which is the "gold standard" in dating very old rock.
Which rock type of the NGB contains fossil structures?
a. greenstone
b. TTG
c. banded iron formation
d. amphibolite
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c. banded iron formation