Word: pasts
(lookup in dictionary)
(lookup stats)
Dates: during 2000-2009
Sort By: most recent first
(reverse)
...climate is clear going back about 800,000 years. Before that, however, it gets murkier. That's largely because ice and air that old haven't yet been found. So scientists rely instead on indirect measurements - and these have led to a climate mystery: some episodes of past warming, including a planetary heat wave about 15 million years ago and another about 3.5 million years ago, seem to have happened without a rise in CO2. No one quite understands why. Maybe other greenhouse gases were the cause - methane, for example. Or maybe it had to do with changes in ocean...
These scientists aren't the first to look at the chemistry of foraminifera; the fossils are abundant in ancient ocean sediments, so they're a particularly good tracer of the past. But they used a new technique to measure CO2: looking at how much of the element boron was present in the foraminifera's shells. When there's lots of CO2 in the air, there's also more in the top layers of seawater, where the relevant species of foraminifera live. That makes the water more acidic, which in turn makes the tiny animals incorporate less boron into their shells...
...Tripati and her colleagues made sure to use two species of foraminifera that are still around ("You can grow them in the lab," she says), just in case the effect varied from one species to another. Beyond that, they compared their own foraminifera-based CO2 estimates for the past 800,000 years with the measurements from the ice caps - and, says Tripati, "they matched to within 20 p.p.m." That makes her and her colleagues confident that the older measurements are valid as well...
...ways. You can be responsible and multiply sketchiness by how many drinks you’ve had, giving you a much lower Non-Sketchy ratio. Do this if you’ve woken up someplace where you don’t remember falling asleep more than once in the past month. Even if you won’t remember, tomorrow, someone else will. On the other hand, you can err on the side of fun and multiply anonymity by how many drinks you’ve had. Do this if you’re 20 years old and still...
...ways. You can be responsible and multiply sketchiness by how many drinks you’ve had, giving you a much lower Non-Sketchy ratio. Do this if you’ve woken up someplace where you don’t remember falling asleep more than once in the past month. Even if you won’t remember, tomorrow, someone else will. On the other hand, you can err on the side of fun and multiply anonymity by how many drinks you’ve had. Do this if you’re 20 years old and still...