Researchers working in Western Australia have discovered the oldest fragments of the Earth’s early crust that have yet been identified: microdiamonds. These microscopic crystals measure only 50 microns across and were formed 4.2 billion years ago. This discovery sheds light on how long it took for the Earth’s crust to form, since this date is only 300 million years after the formation of the Earth itself.
Summary
Western Australian researchers have discovered microdiamonds, the oldest fragments of the Earth’s early crust yet identified. These microscopic crystals were formed 4.2 billion years ago, only 300 million years after the formation of the Earth itself. This discovery sheds light on how long it took for Earth’s crust to form.
Notable Valid Inferences
Earth’s crust did not take longer than 300 million years to begin to form.
A
The Earth’s crust took no longer than 300 million years to start to form.
Must be true. We know this because the microdiamonds researchers found were part of the Earth’s early crust. If the microdiamonds existed 300 million years after Earth itself was formed, then Earth’s crust must have taken no longer than 300 million years to begin to form.
B
The Earth’s crust first formed in the area that is now Western Australia.
Could be false. To claim this is where the Earth’s crust first formed is too extreme. We only know that the microdiamonds the researchers found are the oldest fragments to be found to date. It is possible there exists older fragments that have not yet been found.
C
The Earth’s crust took billions of years to form.
Must be false. We know the microdiamonds the researchers found were part of Earth’s early crust, and these existed only 300 million years after the formation of Earth.
D
Microdiamonds were the first components of the Earth’s crust to form.
Could be false. To claim microdiamonds were the first components is too extreme. We only know that they are the oldest fragments identified to date. It is possible that older fragments exist that have not yet been identified.
E
All naturally occurring microdiamonds were formed at the time the Earth’s crust was being formed.
Could be false. To claim all microdiamonds were formed at this time is too extreme. It is possible that there are other naturally occurring microdiamonds that formed after the ones the researchers identified.
Summary
The hairless dogs in Mexico and Peru must have been transported by boat from one of those two countries to the other, and probably during trade.
Why must they have started in either Mexico or Peru? Well, they wouldn’t have just turned up out of nowhere in both countries. Hairlessness likely didn’t originate twice, so both sets of dogs probably originated a single place.
Why must they have come by boat? They’ve never existed in the wild, so to arrive anywhere else, they must have come with humans. And overland travel between Mexico and Peru was very difficult back when these dogs appeared in those countries.
Why must they have started in either Mexico or Peru? Well, they wouldn’t have just turned up out of nowhere in both countries. Hairlessness likely didn’t originate twice, so both sets of dogs probably originated a single place.
Why must they have come by boat? They’ve never existed in the wild, so to arrive anywhere else, they must have come with humans. And overland travel between Mexico and Peru was very difficult back when these dogs appeared in those countries.
Notable Assumptions
The author hypothesizes that boats are the answer because overland travel would have been so difficult. But he never says whether boats were any easier. He’s implying a comparison (overland harder, boats easier) without actually supporting that comparison. So he must assume that travel between the two countries was indeed easier by boat than by land.
He also assumes that the dogs weren’t transported to both Mexico and Peru from some other location(s).
He also assumes that the dogs weren’t transported to both Mexico and Peru from some other location(s).
A
Hairless dogs have never been found anywhere except in the regions of western Mexico and coastal Peru.
The author assumes the dogs weren’t transported to both Mexico and Peru from some other location(s). But he doesn’t assume they’ve never been found anywhere else. What if they were transported from Mexico to Peru, and then to Argentina? That wouldn’t damage the argument.
B
Most of the trade goods that came into western Mexico centuries ago were transported by boat.
Too strong. The author doesn’t need to assume that most trade from all places to Mexico was by boat. He just needs to assume that there were at least some trade expeditions running between Mexico and Peru.
C
Centuries ago, no one would have traveled between western Mexico and coastal Peru by boat except for the purposes of carrying out a trading expedition.
Too strong. The author doesn’t need to assume that all boat travel was for trading expeditions—just that at least some boat travel was (enough to make it likely that the dogs were on some of those expeditions).
D
If hairless dogs were at one time transported between western Mexico and coastal Peru by boat, they were traded in exchange for other goods.
Whether the dogs were traded during trade expeditions is irrelevant. The author merely assumes that there was some way for the dogs to be present on those expeditions. Perhaps they were brought as gifts rather than exchanged, or perhaps they were there by accident.
E
Centuries ago, it was easier to travel by boat between western Mexico and coastal Peru than to travel by an overland route.
The author implies a comparison between overland and boat travel but never says how difficult boat travel was. He must assume boat travel was easier. Otherwise, if it was just as hard or harder than overland travel, the conclusion becomes unsupported or even anti-supported.
Summary
Ostrich farming requires less land than cattle farming. Ostriches reproduce faster than cattle. Starting in cattle ranching requires a large herd of cows, a bull, and at least two acres per cow. Starting in ostrich farming requires two pairs of yearling ostriches and one acre of land. The start-up costs for ostrich farming is greater than that for cattle farming. Ostrich farming can eventually yield five times the returns as cattle farming.
Strongly Supported Conclusions
Ostrich farming allows farmers to eventually produce greater yields with less land than cattle ranching. Two pairs of yearling ostriches plus one acre of land is more expensive than a large herd of cows, a bull, and two acres per cow.
A
Two pairs of yearling ostriches are more expensive than a herd of cows and a bull.
This is strongly supported since we know that the start-up costs for ostrich farming is higher than that for bull farming, and starting an ostrich farm requires two pairs of yearling ostriches compared to a herd of cows and a bull for cattle ranching.
B
Cattle ranching is not a good source of income.
This is unsupported because even though ostrich farming may yield greater returns than cattle farming (relative statement), cattle farming could still be a good source of income (absolute statement).
C
A cow consumes no more feed than an ostrich does.
This is unsupported because the stimulus never clearly tells us how much cattle and ostriches need to eat.
D
The average ostrich farm generates almost five times as much profit as the average cattle ranch.
This is unsupported because while ostrich farming could potentially yield five times that of cattle ranching, we don’t know that the average ostrich farm is productive enough to reach these maximum possible gains.
E
Ostrich farmers typically lose money during their first year.
This is unsupported because although the startup costs are higher for ostrich farming than cattle farming, it is possible that both are profitable in their first year.
Summarize Argument: Counter-Position
The author concludes that we should not use nutritional supplements in treating the disease. This is based on the fact that Dr Sullivan, who argues in favor of using nutritional supplements to treat the disease, has a personal interest in making that argument, because he’s paid to endorse a line of nutritional supplements.
Identify and Describe Flaw
The author inappropriately attacks the source rather than the merits. Rather than presenting reasons that the nutritional supplement should not be used to treat the disease, the author simply attacks Dr. Sullivan’s motivations in encouraging others to use nutritional supplements. But his self-interest isn’t relevant to whether nutritional supplements are a good idea for treating the disease.
A
relies on two different meanings of the term “supplement” to draw a conclusion
The word “supplement” means the same thing throughout. It’s a dietary addition that one takes for nutrition.
B
relies solely on an appeal to an authority whose trustworthiness should not necessarily be taken for granted
The author’s argument does not rely on an authority. The author never says, “X says we shouldn’t use nutritional supplements, so that’s why we shouldn’t use them.” The author criticizes the source of a claim, but that’s not a reliance on authority.
C
appeals to people’s emotions regarding the treatment of disease rather than to the efficacy of the two approaches to treatment
The author doesn’t appeal to emotions. The author simply points out the self-interest of Dr. Sullivan. There’s no indication that this is supposed to lead to an emotional reaction.
D
criticizes Dr. Sullivan’s motives for holding a position rather than addressing the position itself
The author criticizes Dr. Sullivan’s motives (self-interested due to endorsement of nutritional supplements). But the author doesn’t address why nutritional supplements shouldn’t be used in treating the disease.
E
fails to justify its presumption that nutritional supplements cannot be used in conjunction with other treatments
The author doesn’t assume that nutritional supplements can’t be used in connection with other treatments. The reasoning isn’t, “We should use other treatments, so we can’t use nutritional supplements.”