Current Earth: Plants and animals thrive in balance. Plants take in carbon dioxide CO 2 and give off oxygen O 2. Animals take in oxygen O 2 and give off CO 2. Burning stuff also gives off CO 2. Much of the CO 2 dissolved into the oceans. Modeling Sea Level Rise. The Global Climate System. Earth's Earliest Climate. Methane Hydrates and Contemporary Climate Change. Citation: Hessler, A. Nature Education Knowledge 3 10 Aa Aa Aa. A Habitable Young Earth?
Our Earliest Climate Record. From the Isua terrane at 3. Together with the Pilbara block in Western Australia, these rocks are our oldest subaerial deposits, our oldest direct evidence of interactions between the atmosphere and geosphere. The rocks are, therefore, our oldest record of climate. What do the Barberton rocks tell us about surface temperature?
First, there is no evidence of deposition or erosion by glaciers — no poorly-sorted till, dropstones, or glacial striations on bedrock. Second, there is ample evidence of deposition by liquid water — wave ripples in sandstone, sandstone-shale couplets deposited by tides, dune crossbeds built by storm waves, and well-rounded cobbles transported by rivers Figure 3.
We already know there was freely moving water back at 3. So what new information do the Barberton and Pilbara terranes offer us? An Ancient Greenhouse. Evidence points to an unfrozen — perhaps balmy — Archean Earth, despite a faint Sun. Was a greenhouse atmosphere responsible?
To warm the planet above freezing, models show that the Archean atmosphere would have needed — times more CO 2 than present atmospheric level PAL Kasting Again, we can look to the sedimentary rocks of the Barberton terrane for hard evidence of the ancient concentration of atmospheric CO 2.
This is not as straightforward as it is for our recent climate record 2 in order to precipitate: siderite FeCO 3 and nahcolite NaHCO 3. Example equilibrium reactions show that, depending on temperature, increasing carbon dioxide on the right will force the reaction to the left, to precipitate either siderite Fe-system or nahcolite NaH-system. This range is well below that required by the models Kasting , but these are also minimum values and by themselves do not preclude higher CO 2.
A more recent study Rosing et al. All geologic evidence taken together, the Archean atmosphere likely had 2 , not enough greenhouse to counteract the cooler Sun, based on earlier models Kasting If the concentration of atmospheric CO 2 in the Archean was insufficient, perhaps another greenhouse gas helped fill the gap. Methane CH 4 seems a good candidate. Archean organisms may have been prolific CH 4 producers, prior to the advent of oxygen photosynthesis Kharecha et al.
And in the low-oxygen Archean atmosphere, CH 4 would have had a longer residence time Zahnle , Pavlov et al. However, laboratory experiments have shown that when atmospheric CH 4 concentration approaches that of CO 2 , a hydrocarbon haze is produced Trainer et al. Because a hydrocarbon haze blocks sunlight, a CH 4 —rich atmosphere runs the risk of self-cooling. Therefore, it is likely that while a modest CO 2 - CH 4 greenhouse existed and could have included a thin hydrocarbon haze , a high concentration CO 2 - CH 4 greenhouse may not be plausible Haqq-Misra et al.
Recent models point to increased nitrogen Goldblatt et al. Doubling N 2 PAL could lead to a 4. Where did all this N 2 come from and how was it later removed from the atmosphere to reach current levels? Researchers Mather et al. Up in the Clouds. Albedo during the Archean may have been lower than today if we assume the following Rosing et al.
However, the oldest preserved, clearly emergent blocks 3. Why would Archean clouds be different, more transparent, than they are today? Life, once again, may have been a player. Today, clouds are effective at reflecting sunlight back to space due to the abundance of cloud condensation nuclei CCN , solid surfaces onto which water vapor condenses and forms water droplets.
Non-organic particles dust, salt, soot, etc. A recent model proposes Rosing et al. From the 3. The evolution of oxygenic photosynthesis may have begun prior to 2. However, the real turnover took place at 2. Perhaps, because methane would have been removed by oxidation from the atmosphere, converted to the less-effective greenhouse gas CO 2 Kopp et al. The greenhouse may have been additionally weakened by other events just preceding the 2.
Whatever the cause-and-effect, the early Proterozoic glaciation marked the rise of oxygen-producing cyanobacteria to build our modern oxygenic atmosphere, and the subsequent decline of methane-producing microbes and their carbon-rich atmosphere. Methane potentially declined in response. Deep-Time Climate Change.
We use much of the available data and geologic evidence to understand near-term Perhaps what is most telling is that climate regulation has been a mainstay from the beginning.
Despite large changes in solar energy as well as dramatic impact events, our climate has been perpetually suitable for some form of life. Inorganic processes have played a big part in this regulation, particularly through cycles of outgassing, weathering, albedo, and oceanic circulation associated with plate tectonics. From its origin, life has greatly impacted its climate-atmosphere system — without permanently tipping the balance toward uninhabitability.
However we also see that when conditions reach a tipping point e. As we continue to impact the ocean-atmosphere system, we must look to deep-time climate change — particularly these abrupt and seemingly permanent transitions — to more fully frame our forecasts and design our solutions. References and Recommended Reading Abramov, O. Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable. Flag Content Cancel.
Email your Friend. Submit Cancel. This content is currently under construction. Explore This Subject. No topic rooms are there. Earth and its atmosphere are continuously altered. Plate tectonics shift the continents, raise mountains and move the ocean floor while processes not fully understood alter the climate.
Such constant change has characterized Earth since its beginning some 4. From the outset, heat and gravity shaped the evolution of the planet. These forces were gradually joined by the global effects of the emergence of life. Exploring this past offers us the only possibility of understanding the origin of life and, perhaps, its future.
Scientists used to believe the rocky planets, including Earth, Mercury, Venus and Mars, were created by the rapid gravitational collapse of a dust cloud, a deation giving rise to a dense orb.
In the s the Apollo space program changed this view. Studies of moon craters revealed that these gouges were caused by the impact of objects that were in great abundance about 4. Thereafter, the number of impacts appeared to have quickly decreased.
This observation rejuvenated the theory of accretion postulated by Otto Schmidt. The Russian geophysicist had suggested in that planets grew in size gradually, step by step. According to Schmidt, cosmic dust lumped together to form particulates, particulates became gravel, gravel became small balls, then big balls, then tiny planets, or planetesimals, and, nally, dust became the size of the moon.
As the planetesimals became larger, their numbers decreased. Consequently, the number of collisions between planetesimals, or meteorites, decreased. Fewer items available for accretion meant that it took a long time to build up a large planet. A calculation made by George W. Wetherill of the Carnegie Institution of Washington suggests that about million years could pass between the formation of an object measuring 10 kilometers in diameter and an object the size of Earth.
The process of accretion had significant thermal consequences for Earth, consequences that forcefully directed its evolution. Large bodies slamming into the planet produced immense heat in its interior, melting the cosmic dust found there. The resulting furnace--situated some to kilometers underground and called a magma ocean--was active for millions of years, giving rise to volcanic eruptions.
When Earth was young, heat at the surface caused by volcanism and lava ows from the interior was intensified by the constant bombardment of huge objects, some of them perhaps the size of the moon or even Mars. No life was possible during this period. Beyond clarifying that Earth had formed through accretion, the Apollo program compelled scientists to try to reconstruct the subsequent temporal and physical development of the early Earth.
This undertaking had been considered impossible by founders of geology, including Charles Lyell, to whom the following phrase is attributed: No vestige of a beginning, no prospect for an end. This statement conveys the idea that the young Earth could not be re-created, because its remnants were destroyed by its very activity. But the development of isotope geology in the s had rendered this view obsolete. Their imaginations red by Apollo and the moon ndings, geochemists began to apply this technique to understand the evolution of Earth.
Dating rocks using so-called radioactive clocks allows geologists to work on old terrains that do not contain fossils. The hands of a radioactive clock are isotopes--atoms of the same element that have different atomic weights--and geologic time is measured by the rate of decay of one isotope into another [see "The Earliest History of the Earth," by Derek York; Scientific American , January ].
Among the many clocks, those based on the decay of uranium into lead and of uranium into lead are special. Geochronologists can determine the age of samples by analyzing only the daughter product--in this case, lead--of the radioactive parent, uranium.
In the classic work of Claire C. Patterson of the California Institute of Technology used the uranium-lead clock to establish an age of 4. As Patterson argued, some meteorites were indeed formed about 4. But Earth continued to grow through the bombardment of planetesimals until some million to million years later. At that time This possibility had already been suggested by Bruce R. Doe and Robert E. Zartman of the U. Geological Survey in Denver two decades ago and is in agreement with Wetherills estimates.
The emergence of the continents came somewhat later. According to the theory of plate tectonics, these landmasses are the only part of Earth's crust that is not recycled and, consequently, destroyed during the geothermal cycle driven by the convection in the mantle. Continents thus provide a form of memory because the record of early life can be read in their rocks.
Geologic activity, however, including plate tectonics, erosion and metamorphism, has destroyed almost all the ancient rocks. Very few fragments have survived this geologic machine. Nevertheless, in recent decades, several important nds have been made, again using isotope geochemistry.
One group, led by Stephen Moorbath of the University of Oxford, discovered terrain in West Greenland that is between 3. In addition, Samuel A. Bowring of the Massachusetts Institute of Technology explored a small area in North America--the Acasta gneiss--that is thought to be 3.
Ultimately, a quest for the mineral zircon led other researchers to even more ancient terrain. Typically found in continental rocks, zircon is not dissolved during the process of erosion but is deposited in particle form in sediment.
A few pieces of zircon can therefore survive for billions of years and can serve as a witness to Earths more ancient crust. Lancelot, later at the University of Marseille and now at the University of Nmes, respectively, as well as with the efforts of Moorbath and Allgre. It was a group at the Australian National University in Canberra, directed by William Compston, that was nally successful. The team discovered zircons in western Australia that were between 4.
Zircons have been crucial not only for understanding the age of the continents but for determining when life rst appeared. The earliest fossils of undisputed age were found in Australia and South Africa. These relics of blue-green algae are about 3. Manfred Schidlowski of the Max Planck Institute for Chemistry in Mainz studied the Isua formation in West Greenland and argued that organic matter existed as long ago as 3.
Because most of the record of early life has been destroyed by geologic activity, we cannot say exactly when it rst appeared--perhaps it arose very quickly, maybe even 4. As the Earth cooled down, most of the water vapour condensed and formed the oceans. It is thought that the atmospheres of Mars and Venus today, which contain mostly carbon dioxide, are similar to the early atmosphere of the Earth.
For example, volcanoes release high quantities of carbon dioxide. Iron-based compounds are present in very old rocks that could only have formed if there was little or no oxygen at the time.
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